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Diffstat (limited to 'llvm/lib/Transforms/IPO/GlobalOpt.cpp')
| -rw-r--r-- | llvm/lib/Transforms/IPO/GlobalOpt.cpp | 3046 |
1 files changed, 3046 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp new file mode 100644 index 000000000000..819715b9f8da --- /dev/null +++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp @@ -0,0 +1,3046 @@ +//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This pass transforms simple global variables that never have their address +// taken. If obviously true, it marks read/write globals as constant, deletes +// variables only stored to, etc. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/IPO/GlobalOpt.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/Twine.h" +#include "llvm/ADT/iterator_range.h" +#include "llvm/Analysis/BlockFrequencyInfo.h" +#include "llvm/Analysis/ConstantFolding.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/BinaryFormat/Dwarf.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/CallingConv.h" +#include "llvm/IR/Constant.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DebugInfoMetadata.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GetElementPtrTypeIterator.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalValue.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/InstrTypes.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Operator.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/IR/ValueHandle.h" +#include "llvm/Pass.h" +#include "llvm/Support/AtomicOrdering.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Transforms/IPO.h" +#include "llvm/Transforms/Utils/CtorUtils.h" +#include "llvm/Transforms/Utils/Evaluator.h" +#include "llvm/Transforms/Utils/GlobalStatus.h" +#include <cassert> +#include <cstdint> +#include <utility> +#include <vector> + +using namespace llvm; + +#define DEBUG_TYPE "globalopt" + +STATISTIC(NumMarked , "Number of globals marked constant"); +STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr"); +STATISTIC(NumSRA , "Number of aggregate globals broken into scalars"); +STATISTIC(NumHeapSRA , "Number of heap objects SRA'd"); +STATISTIC(NumSubstitute,"Number of globals with initializers stored into them"); +STATISTIC(NumDeleted , "Number of globals deleted"); +STATISTIC(NumGlobUses , "Number of global uses devirtualized"); +STATISTIC(NumLocalized , "Number of globals localized"); +STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans"); +STATISTIC(NumFastCallFns , "Number of functions converted to fastcc"); +STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated"); +STATISTIC(NumNestRemoved , "Number of nest attributes removed"); +STATISTIC(NumAliasesResolved, "Number of global aliases resolved"); +STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated"); +STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed"); +STATISTIC(NumInternalFunc, "Number of internal functions"); +STATISTIC(NumColdCC, "Number of functions marked coldcc"); + +static cl::opt<bool> + EnableColdCCStressTest("enable-coldcc-stress-test", + cl::desc("Enable stress test of coldcc by adding " + "calling conv to all internal functions."), + cl::init(false), cl::Hidden); + +static cl::opt<int> ColdCCRelFreq( + "coldcc-rel-freq", cl::Hidden, cl::init(2), cl::ZeroOrMore, + cl::desc( + "Maximum block frequency, expressed as a percentage of caller's " + "entry frequency, for a call site to be considered cold for enabling" + "coldcc")); + +/// Is this global variable possibly used by a leak checker as a root? If so, +/// we might not really want to eliminate the stores to it. +static bool isLeakCheckerRoot(GlobalVariable *GV) { + // A global variable is a root if it is a pointer, or could plausibly contain + // a pointer. There are two challenges; one is that we could have a struct + // the has an inner member which is a pointer. We recurse through the type to + // detect these (up to a point). The other is that we may actually be a union + // of a pointer and another type, and so our LLVM type is an integer which + // gets converted into a pointer, or our type is an [i8 x #] with a pointer + // potentially contained here. + + if (GV->hasPrivateLinkage()) + return false; + + SmallVector<Type *, 4> Types; + Types.push_back(GV->getValueType()); + + unsigned Limit = 20; + do { + Type *Ty = Types.pop_back_val(); + switch (Ty->getTypeID()) { + default: break; + case Type::PointerTyID: return true; + case Type::ArrayTyID: + case Type::VectorTyID: { + SequentialType *STy = cast<SequentialType>(Ty); + Types.push_back(STy->getElementType()); + break; + } + case Type::StructTyID: { + StructType *STy = cast<StructType>(Ty); + if (STy->isOpaque()) return true; + for (StructType::element_iterator I = STy->element_begin(), + E = STy->element_end(); I != E; ++I) { + Type *InnerTy = *I; + if (isa<PointerType>(InnerTy)) return true; + if (isa<CompositeType>(InnerTy)) + Types.push_back(InnerTy); + } + break; + } + } + if (--Limit == 0) return true; + } while (!Types.empty()); + return false; +} + +/// Given a value that is stored to a global but never read, determine whether +/// it's safe to remove the store and the chain of computation that feeds the +/// store. +static bool IsSafeComputationToRemove( + Value *V, function_ref<TargetLibraryInfo &(Function &)> GetTLI) { + do { + if (isa<Constant>(V)) + return true; + if (!V->hasOneUse()) + return false; + if (isa<LoadInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V) || + isa<GlobalValue>(V)) + return false; + if (isAllocationFn(V, GetTLI)) + return true; + + Instruction *I = cast<Instruction>(V); + if (I->mayHaveSideEffects()) + return false; + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { + if (!GEP->hasAllConstantIndices()) + return false; + } else if (I->getNumOperands() != 1) { + return false; + } + + V = I->getOperand(0); + } while (true); +} + +/// This GV is a pointer root. Loop over all users of the global and clean up +/// any that obviously don't assign the global a value that isn't dynamically +/// allocated. +static bool +CleanupPointerRootUsers(GlobalVariable *GV, + function_ref<TargetLibraryInfo &(Function &)> GetTLI) { + // A brief explanation of leak checkers. The goal is to find bugs where + // pointers are forgotten, causing an accumulating growth in memory + // usage over time. The common strategy for leak checkers is to whitelist the + // memory pointed to by globals at exit. This is popular because it also + // solves another problem where the main thread of a C++ program may shut down + // before other threads that are still expecting to use those globals. To + // handle that case, we expect the program may create a singleton and never + // destroy it. + + bool Changed = false; + + // If Dead[n].first is the only use of a malloc result, we can delete its + // chain of computation and the store to the global in Dead[n].second. + SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead; + + // Constants can't be pointers to dynamically allocated memory. + for (Value::user_iterator UI = GV->user_begin(), E = GV->user_end(); + UI != E;) { + User *U = *UI++; + if (StoreInst *SI = dyn_cast<StoreInst>(U)) { + Value *V = SI->getValueOperand(); + if (isa<Constant>(V)) { + Changed = true; + SI->eraseFromParent(); + } else if (Instruction *I = dyn_cast<Instruction>(V)) { + if (I->hasOneUse()) + Dead.push_back(std::make_pair(I, SI)); + } + } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(U)) { + if (isa<Constant>(MSI->getValue())) { + Changed = true; + MSI->eraseFromParent(); + } else if (Instruction *I = dyn_cast<Instruction>(MSI->getValue())) { + if (I->hasOneUse()) + Dead.push_back(std::make_pair(I, MSI)); + } + } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(U)) { + GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(MTI->getSource()); + if (MemSrc && MemSrc->isConstant()) { + Changed = true; + MTI->eraseFromParent(); + } else if (Instruction *I = dyn_cast<Instruction>(MemSrc)) { + if (I->hasOneUse()) + Dead.push_back(std::make_pair(I, MTI)); + } + } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { + if (CE->use_empty()) { + CE->destroyConstant(); + Changed = true; + } + } else if (Constant *C = dyn_cast<Constant>(U)) { + if (isSafeToDestroyConstant(C)) { + C->destroyConstant(); + // This could have invalidated UI, start over from scratch. + Dead.clear(); + CleanupPointerRootUsers(GV, GetTLI); + return true; + } + } + } + + for (int i = 0, e = Dead.size(); i != e; ++i) { + if (IsSafeComputationToRemove(Dead[i].first, GetTLI)) { + Dead[i].second->eraseFromParent(); + Instruction *I = Dead[i].first; + do { + if (isAllocationFn(I, GetTLI)) + break; + Instruction *J = dyn_cast<Instruction>(I->getOperand(0)); + if (!J) + break; + I->eraseFromParent(); + I = J; + } while (true); + I->eraseFromParent(); + } + } + + return Changed; +} + +/// We just marked GV constant. Loop over all users of the global, cleaning up +/// the obvious ones. This is largely just a quick scan over the use list to +/// clean up the easy and obvious cruft. This returns true if it made a change. +static bool CleanupConstantGlobalUsers( + Value *V, Constant *Init, const DataLayout &DL, + function_ref<TargetLibraryInfo &(Function &)> GetTLI) { + bool Changed = false; + // Note that we need to use a weak value handle for the worklist items. When + // we delete a constant array, we may also be holding pointer to one of its + // elements (or an element of one of its elements if we're dealing with an + // array of arrays) in the worklist. + SmallVector<WeakTrackingVH, 8> WorkList(V->user_begin(), V->user_end()); + while (!WorkList.empty()) { + Value *UV = WorkList.pop_back_val(); + if (!UV) + continue; + + User *U = cast<User>(UV); + + if (LoadInst *LI = dyn_cast<LoadInst>(U)) { + if (Init) { + // Replace the load with the initializer. + LI->replaceAllUsesWith(Init); + LI->eraseFromParent(); + Changed = true; + } + } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) { + // Store must be unreachable or storing Init into the global. + SI->eraseFromParent(); + Changed = true; + } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) { + if (CE->getOpcode() == Instruction::GetElementPtr) { + Constant *SubInit = nullptr; + if (Init) + SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); + Changed |= CleanupConstantGlobalUsers(CE, SubInit, DL, GetTLI); + } else if ((CE->getOpcode() == Instruction::BitCast && + CE->getType()->isPointerTy()) || + CE->getOpcode() == Instruction::AddrSpaceCast) { + // Pointer cast, delete any stores and memsets to the global. + Changed |= CleanupConstantGlobalUsers(CE, nullptr, DL, GetTLI); + } + + if (CE->use_empty()) { + CE->destroyConstant(); + Changed = true; + } + } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { + // Do not transform "gepinst (gep constexpr (GV))" here, because forming + // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold + // and will invalidate our notion of what Init is. + Constant *SubInit = nullptr; + if (!isa<ConstantExpr>(GEP->getOperand(0))) { + ConstantExpr *CE = dyn_cast_or_null<ConstantExpr>( + ConstantFoldInstruction(GEP, DL, &GetTLI(*GEP->getFunction()))); + if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr) + SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE); + + // If the initializer is an all-null value and we have an inbounds GEP, + // we already know what the result of any load from that GEP is. + // TODO: Handle splats. + if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds()) + SubInit = Constant::getNullValue(GEP->getResultElementType()); + } + Changed |= CleanupConstantGlobalUsers(GEP, SubInit, DL, GetTLI); + + if (GEP->use_empty()) { + GEP->eraseFromParent(); + Changed = true; + } + } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv + if (MI->getRawDest() == V) { + MI->eraseFromParent(); + Changed = true; + } + + } else if (Constant *C = dyn_cast<Constant>(U)) { + // If we have a chain of dead constantexprs or other things dangling from + // us, and if they are all dead, nuke them without remorse. + if (isSafeToDestroyConstant(C)) { + C->destroyConstant(); + CleanupConstantGlobalUsers(V, Init, DL, GetTLI); + return true; + } + } + } + return Changed; +} + +static bool isSafeSROAElementUse(Value *V); + +/// Return true if the specified GEP is a safe user of a derived +/// expression from a global that we want to SROA. +static bool isSafeSROAGEP(User *U) { + // Check to see if this ConstantExpr GEP is SRA'able. In particular, we + // don't like < 3 operand CE's, and we don't like non-constant integer + // indices. This enforces that all uses are 'gep GV, 0, C, ...' for some + // value of C. + if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) || + !cast<Constant>(U->getOperand(1))->isNullValue()) + return false; + + gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U); + ++GEPI; // Skip over the pointer index. + + // For all other level we require that the indices are constant and inrange. + // In particular, consider: A[0][i]. We cannot know that the user isn't doing + // invalid things like allowing i to index an out-of-range subscript that + // accesses A[1]. This can also happen between different members of a struct + // in llvm IR. + for (; GEPI != E; ++GEPI) { + if (GEPI.isStruct()) + continue; + + ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand()); + if (!IdxVal || (GEPI.isBoundedSequential() && + IdxVal->getZExtValue() >= GEPI.getSequentialNumElements())) + return false; + } + + return llvm::all_of(U->users(), + [](User *UU) { return isSafeSROAElementUse(UU); }); +} + +/// Return true if the specified instruction is a safe user of a derived +/// expression from a global that we want to SROA. +static bool isSafeSROAElementUse(Value *V) { + // We might have a dead and dangling constant hanging off of here. + if (Constant *C = dyn_cast<Constant>(V)) + return isSafeToDestroyConstant(C); + + Instruction *I = dyn_cast<Instruction>(V); + if (!I) return false; + + // Loads are ok. + if (isa<LoadInst>(I)) return true; + + // Stores *to* the pointer are ok. + if (StoreInst *SI = dyn_cast<StoreInst>(I)) + return SI->getOperand(0) != V; + + // Otherwise, it must be a GEP. Check it and its users are safe to SRA. + return isa<GetElementPtrInst>(I) && isSafeSROAGEP(I); +} + +/// Look at all uses of the global and decide whether it is safe for us to +/// perform this transformation. +static bool GlobalUsersSafeToSRA(GlobalValue *GV) { + for (User *U : GV->users()) { + // The user of the global must be a GEP Inst or a ConstantExpr GEP. + if (!isa<GetElementPtrInst>(U) && + (!isa<ConstantExpr>(U) || + cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr)) + return false; + + // Check the gep and it's users are safe to SRA + if (!isSafeSROAGEP(U)) + return false; + } + + return true; +} + +/// Copy over the debug info for a variable to its SRA replacements. +static void transferSRADebugInfo(GlobalVariable *GV, GlobalVariable *NGV, + uint64_t FragmentOffsetInBits, + uint64_t FragmentSizeInBits, + unsigned NumElements) { + SmallVector<DIGlobalVariableExpression *, 1> GVs; + GV->getDebugInfo(GVs); + for (auto *GVE : GVs) { + DIVariable *Var = GVE->getVariable(); + DIExpression *Expr = GVE->getExpression(); + if (NumElements > 1) { + if (auto E = DIExpression::createFragmentExpression( + Expr, FragmentOffsetInBits, FragmentSizeInBits)) + Expr = *E; + else + return; + } + auto *NGVE = DIGlobalVariableExpression::get(GVE->getContext(), Var, Expr); + NGV->addDebugInfo(NGVE); + } +} + +/// Perform scalar replacement of aggregates on the specified global variable. +/// This opens the door for other optimizations by exposing the behavior of the +/// program in a more fine-grained way. We have determined that this +/// transformation is safe already. We return the first global variable we +/// insert so that the caller can reprocess it. +static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) { + // Make sure this global only has simple uses that we can SRA. + if (!GlobalUsersSafeToSRA(GV)) + return nullptr; + + assert(GV->hasLocalLinkage()); + Constant *Init = GV->getInitializer(); + Type *Ty = Init->getType(); + + std::vector<GlobalVariable *> NewGlobals; + Module::GlobalListType &Globals = GV->getParent()->getGlobalList(); + + // Get the alignment of the global, either explicit or target-specific. + unsigned StartAlignment = GV->getAlignment(); + if (StartAlignment == 0) + StartAlignment = DL.getABITypeAlignment(GV->getType()); + + if (StructType *STy = dyn_cast<StructType>(Ty)) { + unsigned NumElements = STy->getNumElements(); + NewGlobals.reserve(NumElements); + const StructLayout &Layout = *DL.getStructLayout(STy); + for (unsigned i = 0, e = NumElements; i != e; ++i) { + Constant *In = Init->getAggregateElement(i); + assert(In && "Couldn't get element of initializer?"); + GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false, + GlobalVariable::InternalLinkage, + In, GV->getName()+"."+Twine(i), + GV->getThreadLocalMode(), + GV->getType()->getAddressSpace()); + NGV->setExternallyInitialized(GV->isExternallyInitialized()); + NGV->copyAttributesFrom(GV); + Globals.push_back(NGV); + NewGlobals.push_back(NGV); + + // Calculate the known alignment of the field. If the original aggregate + // had 256 byte alignment for example, something might depend on that: + // propagate info to each field. + uint64_t FieldOffset = Layout.getElementOffset(i); + Align NewAlign(MinAlign(StartAlignment, FieldOffset)); + if (NewAlign > Align(DL.getABITypeAlignment(STy->getElementType(i)))) + NGV->setAlignment(NewAlign); + + // Copy over the debug info for the variable. + uint64_t Size = DL.getTypeAllocSizeInBits(NGV->getValueType()); + uint64_t FragmentOffsetInBits = Layout.getElementOffsetInBits(i); + transferSRADebugInfo(GV, NGV, FragmentOffsetInBits, Size, NumElements); + } + } else if (SequentialType *STy = dyn_cast<SequentialType>(Ty)) { + unsigned NumElements = STy->getNumElements(); + if (NumElements > 16 && GV->hasNUsesOrMore(16)) + return nullptr; // It's not worth it. + NewGlobals.reserve(NumElements); + auto ElTy = STy->getElementType(); + uint64_t EltSize = DL.getTypeAllocSize(ElTy); + Align EltAlign(DL.getABITypeAlignment(ElTy)); + uint64_t FragmentSizeInBits = DL.getTypeAllocSizeInBits(ElTy); + for (unsigned i = 0, e = NumElements; i != e; ++i) { + Constant *In = Init->getAggregateElement(i); + assert(In && "Couldn't get element of initializer?"); + + GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false, + GlobalVariable::InternalLinkage, + In, GV->getName()+"."+Twine(i), + GV->getThreadLocalMode(), + GV->getType()->getAddressSpace()); + NGV->setExternallyInitialized(GV->isExternallyInitialized()); + NGV->copyAttributesFrom(GV); + Globals.push_back(NGV); + NewGlobals.push_back(NGV); + + // Calculate the known alignment of the field. If the original aggregate + // had 256 byte alignment for example, something might depend on that: + // propagate info to each field. + Align NewAlign(MinAlign(StartAlignment, EltSize * i)); + if (NewAlign > EltAlign) + NGV->setAlignment(NewAlign); + transferSRADebugInfo(GV, NGV, FragmentSizeInBits * i, FragmentSizeInBits, + NumElements); + } + } + + if (NewGlobals.empty()) + return nullptr; + + LLVM_DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV << "\n"); + + Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext())); + + // Loop over all of the uses of the global, replacing the constantexpr geps, + // with smaller constantexpr geps or direct references. + while (!GV->use_empty()) { + User *GEP = GV->user_back(); + assert(((isa<ConstantExpr>(GEP) && + cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)|| + isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!"); + + // Ignore the 1th operand, which has to be zero or else the program is quite + // broken (undefined). Get the 2nd operand, which is the structure or array + // index. + unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue(); + if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access. + + Value *NewPtr = NewGlobals[Val]; + Type *NewTy = NewGlobals[Val]->getValueType(); + + // Form a shorter GEP if needed. + if (GEP->getNumOperands() > 3) { + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) { + SmallVector<Constant*, 8> Idxs; + Idxs.push_back(NullInt); + for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i) + Idxs.push_back(CE->getOperand(i)); + NewPtr = + ConstantExpr::getGetElementPtr(NewTy, cast<Constant>(NewPtr), Idxs); + } else { + GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP); + SmallVector<Value*, 8> Idxs; + Idxs.push_back(NullInt); + for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i) + Idxs.push_back(GEPI->getOperand(i)); + NewPtr = GetElementPtrInst::Create( + NewTy, NewPtr, Idxs, GEPI->getName() + "." + Twine(Val), GEPI); + } + } + GEP->replaceAllUsesWith(NewPtr); + + if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP)) + GEPI->eraseFromParent(); + else + cast<ConstantExpr>(GEP)->destroyConstant(); + } + + // Delete the old global, now that it is dead. + Globals.erase(GV); + ++NumSRA; + + // Loop over the new globals array deleting any globals that are obviously + // dead. This can arise due to scalarization of a structure or an array that + // has elements that are dead. + unsigned FirstGlobal = 0; + for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i) + if (NewGlobals[i]->use_empty()) { + Globals.erase(NewGlobals[i]); + if (FirstGlobal == i) ++FirstGlobal; + } + + return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : nullptr; +} + +/// Return true if all users of the specified value will trap if the value is +/// dynamically null. PHIs keeps track of any phi nodes we've seen to avoid +/// reprocessing them. +static bool AllUsesOfValueWillTrapIfNull(const Value *V, + SmallPtrSetImpl<const PHINode*> &PHIs) { + for (const User *U : V->users()) { + if (const Instruction *I = dyn_cast<Instruction>(U)) { + // If null pointer is considered valid, then all uses are non-trapping. + // Non address-space 0 globals have already been pruned by the caller. + if (NullPointerIsDefined(I->getFunction())) + return false; + } + if (isa<LoadInst>(U)) { + // Will trap. + } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) { + if (SI->getOperand(0) == V) { + //cerr << "NONTRAPPING USE: " << *U; + return false; // Storing the value. + } + } else if (const CallInst *CI = dyn_cast<CallInst>(U)) { + if (CI->getCalledValue() != V) { + //cerr << "NONTRAPPING USE: " << *U; + return false; // Not calling the ptr + } + } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) { + if (II->getCalledValue() != V) { + //cerr << "NONTRAPPING USE: " << *U; + return false; // Not calling the ptr + } + } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) { + if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false; + } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { + if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false; + } else if (const PHINode *PN = dyn_cast<PHINode>(U)) { + // If we've already seen this phi node, ignore it, it has already been + // checked. + if (PHIs.insert(PN).second && !AllUsesOfValueWillTrapIfNull(PN, PHIs)) + return false; + } else if (isa<ICmpInst>(U) && + isa<ConstantPointerNull>(U->getOperand(1))) { + // Ignore icmp X, null + } else { + //cerr << "NONTRAPPING USE: " << *U; + return false; + } + } + return true; +} + +/// Return true if all uses of any loads from GV will trap if the loaded value +/// is null. Note that this also permits comparisons of the loaded value +/// against null, as a special case. +static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) { + for (const User *U : GV->users()) + if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { + SmallPtrSet<const PHINode*, 8> PHIs; + if (!AllUsesOfValueWillTrapIfNull(LI, PHIs)) + return false; + } else if (isa<StoreInst>(U)) { + // Ignore stores to the global. + } else { + // We don't know or understand this user, bail out. + //cerr << "UNKNOWN USER OF GLOBAL!: " << *U; + return false; + } + return true; +} + +static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) { + bool Changed = false; + for (auto UI = V->user_begin(), E = V->user_end(); UI != E; ) { + Instruction *I = cast<Instruction>(*UI++); + // Uses are non-trapping if null pointer is considered valid. + // Non address-space 0 globals are already pruned by the caller. + if (NullPointerIsDefined(I->getFunction())) + return false; + if (LoadInst *LI = dyn_cast<LoadInst>(I)) { + LI->setOperand(0, NewV); + Changed = true; + } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) { + if (SI->getOperand(1) == V) { + SI->setOperand(1, NewV); + Changed = true; + } + } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) { + CallSite CS(I); + if (CS.getCalledValue() == V) { + // Calling through the pointer! Turn into a direct call, but be careful + // that the pointer is not also being passed as an argument. + CS.setCalledFunction(NewV); + Changed = true; + bool PassedAsArg = false; + for (unsigned i = 0, e = CS.arg_size(); i != e; ++i) + if (CS.getArgument(i) == V) { + PassedAsArg = true; + CS.setArgument(i, NewV); + } + + if (PassedAsArg) { + // Being passed as an argument also. Be careful to not invalidate UI! + UI = V->user_begin(); + } + } + } else if (CastInst *CI = dyn_cast<CastInst>(I)) { + Changed |= OptimizeAwayTrappingUsesOfValue(CI, + ConstantExpr::getCast(CI->getOpcode(), + NewV, CI->getType())); + if (CI->use_empty()) { + Changed = true; + CI->eraseFromParent(); + } + } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { + // Should handle GEP here. + SmallVector<Constant*, 8> Idxs; + Idxs.reserve(GEPI->getNumOperands()-1); + for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end(); + i != e; ++i) + if (Constant *C = dyn_cast<Constant>(*i)) + Idxs.push_back(C); + else + break; + if (Idxs.size() == GEPI->getNumOperands()-1) + Changed |= OptimizeAwayTrappingUsesOfValue( + GEPI, ConstantExpr::getGetElementPtr(GEPI->getSourceElementType(), + NewV, Idxs)); + if (GEPI->use_empty()) { + Changed = true; + GEPI->eraseFromParent(); + } + } + } + + return Changed; +} + +/// The specified global has only one non-null value stored into it. If there +/// are uses of the loaded value that would trap if the loaded value is +/// dynamically null, then we know that they cannot be reachable with a null +/// optimize away the load. +static bool OptimizeAwayTrappingUsesOfLoads( + GlobalVariable *GV, Constant *LV, const DataLayout &DL, + function_ref<TargetLibraryInfo &(Function &)> GetTLI) { + bool Changed = false; + + // Keep track of whether we are able to remove all the uses of the global + // other than the store that defines it. + bool AllNonStoreUsesGone = true; + + // Replace all uses of loads with uses of uses of the stored value. + for (Value::user_iterator GUI = GV->user_begin(), E = GV->user_end(); GUI != E;){ + User *GlobalUser = *GUI++; + if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) { + Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV); + // If we were able to delete all uses of the loads + if (LI->use_empty()) { + LI->eraseFromParent(); + Changed = true; + } else { + AllNonStoreUsesGone = false; + } + } else if (isa<StoreInst>(GlobalUser)) { + // Ignore the store that stores "LV" to the global. + assert(GlobalUser->getOperand(1) == GV && + "Must be storing *to* the global"); + } else { + AllNonStoreUsesGone = false; + + // If we get here we could have other crazy uses that are transitively + // loaded. + assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) || + isa<ConstantExpr>(GlobalUser) || isa<CmpInst>(GlobalUser) || + isa<BitCastInst>(GlobalUser) || + isa<GetElementPtrInst>(GlobalUser)) && + "Only expect load and stores!"); + } + } + + if (Changed) { + LLVM_DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV + << "\n"); + ++NumGlobUses; + } + + // If we nuked all of the loads, then none of the stores are needed either, + // nor is the global. + if (AllNonStoreUsesGone) { + if (isLeakCheckerRoot(GV)) { + Changed |= CleanupPointerRootUsers(GV, GetTLI); + } else { + Changed = true; + CleanupConstantGlobalUsers(GV, nullptr, DL, GetTLI); + } + if (GV->use_empty()) { + LLVM_DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n"); + Changed = true; + GV->eraseFromParent(); + ++NumDeleted; + } + } + return Changed; +} + +/// Walk the use list of V, constant folding all of the instructions that are +/// foldable. +static void ConstantPropUsersOf(Value *V, const DataLayout &DL, + TargetLibraryInfo *TLI) { + for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; ) + if (Instruction *I = dyn_cast<Instruction>(*UI++)) + if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) { + I->replaceAllUsesWith(NewC); + + // Advance UI to the next non-I use to avoid invalidating it! + // Instructions could multiply use V. + while (UI != E && *UI == I) + ++UI; + if (isInstructionTriviallyDead(I, TLI)) + I->eraseFromParent(); + } +} + +/// This function takes the specified global variable, and transforms the +/// program as if it always contained the result of the specified malloc. +/// Because it is always the result of the specified malloc, there is no reason +/// to actually DO the malloc. Instead, turn the malloc into a global, and any +/// loads of GV as uses of the new global. +static GlobalVariable * +OptimizeGlobalAddressOfMalloc(GlobalVariable *GV, CallInst *CI, Type *AllocTy, + ConstantInt *NElements, const DataLayout &DL, + TargetLibraryInfo *TLI) { + LLVM_DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI + << '\n'); + + Type *GlobalType; + if (NElements->getZExtValue() == 1) + GlobalType = AllocTy; + else + // If we have an array allocation, the global variable is of an array. + GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue()); + + // Create the new global variable. The contents of the malloc'd memory is + // undefined, so initialize with an undef value. + GlobalVariable *NewGV = new GlobalVariable( + *GV->getParent(), GlobalType, false, GlobalValue::InternalLinkage, + UndefValue::get(GlobalType), GV->getName() + ".body", nullptr, + GV->getThreadLocalMode()); + + // If there are bitcast users of the malloc (which is typical, usually we have + // a malloc + bitcast) then replace them with uses of the new global. Update + // other users to use the global as well. + BitCastInst *TheBC = nullptr; + while (!CI->use_empty()) { + Instruction *User = cast<Instruction>(CI->user_back()); + if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) { + if (BCI->getType() == NewGV->getType()) { + BCI->replaceAllUsesWith(NewGV); + BCI->eraseFromParent(); + } else { + BCI->setOperand(0, NewGV); + } + } else { + if (!TheBC) + TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI); + User->replaceUsesOfWith(CI, TheBC); + } + } + + Constant *RepValue = NewGV; + if (NewGV->getType() != GV->getValueType()) + RepValue = ConstantExpr::getBitCast(RepValue, GV->getValueType()); + + // If there is a comparison against null, we will insert a global bool to + // keep track of whether the global was initialized yet or not. + GlobalVariable *InitBool = + new GlobalVariable(Type::getInt1Ty(GV->getContext()), false, + GlobalValue::InternalLinkage, + ConstantInt::getFalse(GV->getContext()), + GV->getName()+".init", GV->getThreadLocalMode()); + bool InitBoolUsed = false; + + // Loop over all uses of GV, processing them in turn. + while (!GV->use_empty()) { + if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) { + // The global is initialized when the store to it occurs. + new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, + None, SI->getOrdering(), SI->getSyncScopeID(), SI); + SI->eraseFromParent(); + continue; + } + + LoadInst *LI = cast<LoadInst>(GV->user_back()); + while (!LI->use_empty()) { + Use &LoadUse = *LI->use_begin(); + ICmpInst *ICI = dyn_cast<ICmpInst>(LoadUse.getUser()); + if (!ICI) { + LoadUse = RepValue; + continue; + } + + // Replace the cmp X, 0 with a use of the bool value. + // Sink the load to where the compare was, if atomic rules allow us to. + Value *LV = new LoadInst(InitBool->getValueType(), InitBool, + InitBool->getName() + ".val", false, None, + LI->getOrdering(), LI->getSyncScopeID(), + LI->isUnordered() ? (Instruction *)ICI : LI); + InitBoolUsed = true; + switch (ICI->getPredicate()) { + default: llvm_unreachable("Unknown ICmp Predicate!"); + case ICmpInst::ICMP_ULT: + case ICmpInst::ICMP_SLT: // X < null -> always false + LV = ConstantInt::getFalse(GV->getContext()); + break; + case ICmpInst::ICMP_ULE: + case ICmpInst::ICMP_SLE: + case ICmpInst::ICMP_EQ: + LV = BinaryOperator::CreateNot(LV, "notinit", ICI); + break; + case ICmpInst::ICMP_NE: + case ICmpInst::ICMP_UGE: + case ICmpInst::ICMP_SGE: + case ICmpInst::ICMP_UGT: + case ICmpInst::ICMP_SGT: + break; // no change. + } + ICI->replaceAllUsesWith(LV); + ICI->eraseFromParent(); + } + LI->eraseFromParent(); + } + + // If the initialization boolean was used, insert it, otherwise delete it. + if (!InitBoolUsed) { + while (!InitBool->use_empty()) // Delete initializations + cast<StoreInst>(InitBool->user_back())->eraseFromParent(); + delete InitBool; + } else + GV->getParent()->getGlobalList().insert(GV->getIterator(), InitBool); + + // Now the GV is dead, nuke it and the malloc.. + GV->eraseFromParent(); + CI->eraseFromParent(); + + // To further other optimizations, loop over all users of NewGV and try to + // constant prop them. This will promote GEP instructions with constant + // indices into GEP constant-exprs, which will allow global-opt to hack on it. + ConstantPropUsersOf(NewGV, DL, TLI); + if (RepValue != NewGV) + ConstantPropUsersOf(RepValue, DL, TLI); + + return NewGV; +} + +/// Scan the use-list of V checking to make sure that there are no complex uses +/// of V. We permit simple things like dereferencing the pointer, but not +/// storing through the address, unless it is to the specified global. +static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V, + const GlobalVariable *GV, + SmallPtrSetImpl<const PHINode*> &PHIs) { + for (const User *U : V->users()) { + const Instruction *Inst = cast<Instruction>(U); + + if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) { + continue; // Fine, ignore. + } + + if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + if (SI->getOperand(0) == V && SI->getOperand(1) != GV) + return false; // Storing the pointer itself... bad. + continue; // Otherwise, storing through it, or storing into GV... fine. + } + + // Must index into the array and into the struct. + if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) { + if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs)) + return false; + continue; + } + + if (const PHINode *PN = dyn_cast<PHINode>(Inst)) { + // PHIs are ok if all uses are ok. Don't infinitely recurse through PHI + // cycles. + if (PHIs.insert(PN).second) + if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs)) + return false; + continue; + } + + if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) { + if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs)) + return false; + continue; + } + + return false; + } + return true; +} + +/// The Alloc pointer is stored into GV somewhere. Transform all uses of the +/// allocation into loads from the global and uses of the resultant pointer. +/// Further, delete the store into GV. This assumes that these value pass the +/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate. +static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, + GlobalVariable *GV) { + while (!Alloc->use_empty()) { + Instruction *U = cast<Instruction>(*Alloc->user_begin()); + Instruction *InsertPt = U; + if (StoreInst *SI = dyn_cast<StoreInst>(U)) { + // If this is the store of the allocation into the global, remove it. + if (SI->getOperand(1) == GV) { + SI->eraseFromParent(); + continue; + } + } else if (PHINode *PN = dyn_cast<PHINode>(U)) { + // Insert the load in the corresponding predecessor, not right before the + // PHI. + InsertPt = PN->getIncomingBlock(*Alloc->use_begin())->getTerminator(); + } else if (isa<BitCastInst>(U)) { + // Must be bitcast between the malloc and store to initialize the global. + ReplaceUsesOfMallocWithGlobal(U, GV); + U->eraseFromParent(); + continue; + } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) { + // If this is a "GEP bitcast" and the user is a store to the global, then + // just process it as a bitcast. + if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse()) + if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->user_back())) + if (SI->getOperand(1) == GV) { + // Must be bitcast GEP between the malloc and store to initialize + // the global. + ReplaceUsesOfMallocWithGlobal(GEPI, GV); + GEPI->eraseFromParent(); + continue; + } + } + + // Insert a load from the global, and use it instead of the malloc. + Value *NL = + new LoadInst(GV->getValueType(), GV, GV->getName() + ".val", InsertPt); + U->replaceUsesOfWith(Alloc, NL); + } +} + +/// Verify that all uses of V (a load, or a phi of a load) are simple enough to +/// perform heap SRA on. This permits GEP's that index through the array and +/// struct field, icmps of null, and PHIs. +static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V, + SmallPtrSetImpl<const PHINode*> &LoadUsingPHIs, + SmallPtrSetImpl<const PHINode*> &LoadUsingPHIsPerLoad) { + // We permit two users of the load: setcc comparing against the null + // pointer, and a getelementptr of a specific form. + for (const User *U : V->users()) { + const Instruction *UI = cast<Instruction>(U); + + // Comparison against null is ok. + if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UI)) { + if (!isa<ConstantPointerNull>(ICI->getOperand(1))) + return false; + continue; + } + + // getelementptr is also ok, but only a simple form. + if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(UI)) { + // Must index into the array and into the struct. + if (GEPI->getNumOperands() < 3) + return false; + + // Otherwise the GEP is ok. + continue; + } + + if (const PHINode *PN = dyn_cast<PHINode>(UI)) { + if (!LoadUsingPHIsPerLoad.insert(PN).second) + // This means some phi nodes are dependent on each other. + // Avoid infinite looping! + return false; + if (!LoadUsingPHIs.insert(PN).second) + // If we have already analyzed this PHI, then it is safe. + continue; + + // Make sure all uses of the PHI are simple enough to transform. + if (!LoadUsesSimpleEnoughForHeapSRA(PN, + LoadUsingPHIs, LoadUsingPHIsPerLoad)) + return false; + + continue; + } + + // Otherwise we don't know what this is, not ok. + return false; + } + + return true; +} + +/// If all users of values loaded from GV are simple enough to perform HeapSRA, +/// return true. +static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV, + Instruction *StoredVal) { + SmallPtrSet<const PHINode*, 32> LoadUsingPHIs; + SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad; + for (const User *U : GV->users()) + if (const LoadInst *LI = dyn_cast<LoadInst>(U)) { + if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs, + LoadUsingPHIsPerLoad)) + return false; + LoadUsingPHIsPerLoad.clear(); + } + + // If we reach here, we know that all uses of the loads and transitive uses + // (through PHI nodes) are simple enough to transform. However, we don't know + // that all inputs the to the PHI nodes are in the same equivalence sets. + // Check to verify that all operands of the PHIs are either PHIS that can be + // transformed, loads from GV, or MI itself. + for (const PHINode *PN : LoadUsingPHIs) { + for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) { + Value *InVal = PN->getIncomingValue(op); + + // PHI of the stored value itself is ok. + if (InVal == StoredVal) continue; + + if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) { + // One of the PHIs in our set is (optimistically) ok. + if (LoadUsingPHIs.count(InPN)) + continue; + return false; + } + + // Load from GV is ok. + if (const LoadInst *LI = dyn_cast<LoadInst>(InVal)) + if (LI->getOperand(0) == GV) + continue; + + // UNDEF? NULL? + + // Anything else is rejected. + return false; + } + } + + return true; +} + +static Value *GetHeapSROAValue(Value *V, unsigned FieldNo, + DenseMap<Value *, std::vector<Value *>> &InsertedScalarizedValues, + std::vector<std::pair<PHINode *, unsigned>> &PHIsToRewrite) { + std::vector<Value *> &FieldVals = InsertedScalarizedValues[V]; + + if (FieldNo >= FieldVals.size()) + FieldVals.resize(FieldNo+1); + + // If we already have this value, just reuse the previously scalarized + // version. + if (Value *FieldVal = FieldVals[FieldNo]) + return FieldVal; + + // Depending on what instruction this is, we have several cases. + Value *Result; + if (LoadInst *LI = dyn_cast<LoadInst>(V)) { + // This is a scalarized version of the load from the global. Just create + // a new Load of the scalarized global. + Value *V = GetHeapSROAValue(LI->getOperand(0), FieldNo, + InsertedScalarizedValues, PHIsToRewrite); + Result = new LoadInst(V->getType()->getPointerElementType(), V, + LI->getName() + ".f" + Twine(FieldNo), LI); + } else { + PHINode *PN = cast<PHINode>(V); + // PN's type is pointer to struct. Make a new PHI of pointer to struct + // field. + + PointerType *PTy = cast<PointerType>(PN->getType()); + StructType *ST = cast<StructType>(PTy->getElementType()); + + unsigned AS = PTy->getAddressSpace(); + PHINode *NewPN = + PHINode::Create(PointerType::get(ST->getElementType(FieldNo), AS), + PN->getNumIncomingValues(), + PN->getName()+".f"+Twine(FieldNo), PN); + Result = NewPN; + PHIsToRewrite.push_back(std::make_pair(PN, FieldNo)); + } + + return FieldVals[FieldNo] = Result; +} + +/// Given a load instruction and a value derived from the load, rewrite the +/// derived value to use the HeapSRoA'd load. +static void RewriteHeapSROALoadUser(Instruction *LoadUser, + DenseMap<Value *, std::vector<Value *>> &InsertedScalarizedValues, + std::vector<std::pair<PHINode *, unsigned>> &PHIsToRewrite) { + // If this is a comparison against null, handle it. + if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) { + assert(isa<ConstantPointerNull>(SCI->getOperand(1))); + // If we have a setcc of the loaded pointer, we can use a setcc of any + // field. + Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0, + InsertedScalarizedValues, PHIsToRewrite); + + Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr, + Constant::getNullValue(NPtr->getType()), + SCI->getName()); + SCI->replaceAllUsesWith(New); + SCI->eraseFromParent(); + return; + } + + // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...' + if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) { + assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2)) + && "Unexpected GEPI!"); + + // Load the pointer for this field. + unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue(); + Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo, + InsertedScalarizedValues, PHIsToRewrite); + + // Create the new GEP idx vector. + SmallVector<Value*, 8> GEPIdx; + GEPIdx.push_back(GEPI->getOperand(1)); + GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end()); + + Value *NGEPI = GetElementPtrInst::Create(GEPI->getResultElementType(), NewPtr, GEPIdx, + GEPI->getName(), GEPI); + GEPI->replaceAllUsesWith(NGEPI); + GEPI->eraseFromParent(); + return; + } + + // Recursively transform the users of PHI nodes. This will lazily create the + // PHIs that are needed for individual elements. Keep track of what PHIs we + // see in InsertedScalarizedValues so that we don't get infinite loops (very + // antisocial). If the PHI is already in InsertedScalarizedValues, it has + // already been seen first by another load, so its uses have already been + // processed. + PHINode *PN = cast<PHINode>(LoadUser); + if (!InsertedScalarizedValues.insert(std::make_pair(PN, + std::vector<Value *>())).second) + return; + + // If this is the first time we've seen this PHI, recursively process all + // users. + for (auto UI = PN->user_begin(), E = PN->user_end(); UI != E;) { + Instruction *User = cast<Instruction>(*UI++); + RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); + } +} + +/// We are performing Heap SRoA on a global. Ptr is a value loaded from the +/// global. Eliminate all uses of Ptr, making them use FieldGlobals instead. +/// All uses of loaded values satisfy AllGlobalLoadUsesSimpleEnoughForHeapSRA. +static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load, + DenseMap<Value *, std::vector<Value *>> &InsertedScalarizedValues, + std::vector<std::pair<PHINode *, unsigned> > &PHIsToRewrite) { + for (auto UI = Load->user_begin(), E = Load->user_end(); UI != E;) { + Instruction *User = cast<Instruction>(*UI++); + RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite); + } + + if (Load->use_empty()) { + Load->eraseFromParent(); + InsertedScalarizedValues.erase(Load); + } +} + +/// CI is an allocation of an array of structures. Break it up into multiple +/// allocations of arrays of the fields. +static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI, + Value *NElems, const DataLayout &DL, + const TargetLibraryInfo *TLI) { + LLVM_DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << " MALLOC = " << *CI + << '\n'); + Type *MAT = getMallocAllocatedType(CI, TLI); + StructType *STy = cast<StructType>(MAT); + + // There is guaranteed to be at least one use of the malloc (storing + // it into GV). If there are other uses, change them to be uses of + // the global to simplify later code. This also deletes the store + // into GV. + ReplaceUsesOfMallocWithGlobal(CI, GV); + + // Okay, at this point, there are no users of the malloc. Insert N + // new mallocs at the same place as CI, and N globals. + std::vector<Value *> FieldGlobals; + std::vector<Value *> FieldMallocs; + + SmallVector<OperandBundleDef, 1> OpBundles; + CI->getOperandBundlesAsDefs(OpBundles); + + unsigned AS = GV->getType()->getPointerAddressSpace(); + for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){ + Type *FieldTy = STy->getElementType(FieldNo); + PointerType *PFieldTy = PointerType::get(FieldTy, AS); + + GlobalVariable *NGV = new GlobalVariable( + *GV->getParent(), PFieldTy, false, GlobalValue::InternalLinkage, + Constant::getNullValue(PFieldTy), GV->getName() + ".f" + Twine(FieldNo), + nullptr, GV->getThreadLocalMode()); + NGV->copyAttributesFrom(GV); + FieldGlobals.push_back(NGV); + + unsigned TypeSize = DL.getTypeAllocSize(FieldTy); + if (StructType *ST = dyn_cast<StructType>(FieldTy)) + TypeSize = DL.getStructLayout(ST)->getSizeInBytes(); + Type *IntPtrTy = DL.getIntPtrType(CI->getType()); + Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy, + ConstantInt::get(IntPtrTy, TypeSize), + NElems, OpBundles, nullptr, + CI->getName() + ".f" + Twine(FieldNo)); + FieldMallocs.push_back(NMI); + new StoreInst(NMI, NGV, CI); + } + + // The tricky aspect of this transformation is handling the case when malloc + // fails. In the original code, malloc failing would set the result pointer + // of malloc to null. In this case, some mallocs could succeed and others + // could fail. As such, we emit code that looks like this: + // F0 = malloc(field0) + // F1 = malloc(field1) + // F2 = malloc(field2) + // if (F0 == 0 || F1 == 0 || F2 == 0) { + // if (F0) { free(F0); F0 = 0; } + // if (F1) { free(F1); F1 = 0; } + // if (F2) { free(F2); F2 = 0; } + // } + // The malloc can also fail if its argument is too large. + Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0); + Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0), + ConstantZero, "isneg"); + for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) { + Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i], + Constant::getNullValue(FieldMallocs[i]->getType()), + "isnull"); + RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI); + } + + // Split the basic block at the old malloc. + BasicBlock *OrigBB = CI->getParent(); + BasicBlock *ContBB = + OrigBB->splitBasicBlock(CI->getIterator(), "malloc_cont"); + + // Create the block to check the first condition. Put all these blocks at the + // end of the function as they are unlikely to be executed. + BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(), + "malloc_ret_null", + OrigBB->getParent()); + + // Remove the uncond branch from OrigBB to ContBB, turning it into a cond + // branch on RunningOr. + OrigBB->getTerminator()->eraseFromParent(); + BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB); + + // Within the NullPtrBlock, we need to emit a comparison and branch for each + // pointer, because some may be null while others are not. + for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { + Value *GVVal = + new LoadInst(cast<GlobalVariable>(FieldGlobals[i])->getValueType(), + FieldGlobals[i], "tmp", NullPtrBlock); + Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal, + Constant::getNullValue(GVVal->getType())); + BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it", + OrigBB->getParent()); + BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next", + OrigBB->getParent()); + Instruction *BI = BranchInst::Create(FreeBlock, NextBlock, + Cmp, NullPtrBlock); + + // Fill in FreeBlock. + CallInst::CreateFree(GVVal, OpBundles, BI); + new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i], + FreeBlock); + BranchInst::Create(NextBlock, FreeBlock); + + NullPtrBlock = NextBlock; + } + + BranchInst::Create(ContBB, NullPtrBlock); + + // CI is no longer needed, remove it. + CI->eraseFromParent(); + + /// As we process loads, if we can't immediately update all uses of the load, + /// keep track of what scalarized loads are inserted for a given load. + DenseMap<Value *, std::vector<Value *>> InsertedScalarizedValues; + InsertedScalarizedValues[GV] = FieldGlobals; + + std::vector<std::pair<PHINode *, unsigned>> PHIsToRewrite; + + // Okay, the malloc site is completely handled. All of the uses of GV are now + // loads, and all uses of those loads are simple. Rewrite them to use loads + // of the per-field globals instead. + for (auto UI = GV->user_begin(), E = GV->user_end(); UI != E;) { + Instruction *User = cast<Instruction>(*UI++); + + if (LoadInst *LI = dyn_cast<LoadInst>(User)) { + RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite); + continue; + } + + // Must be a store of null. + StoreInst *SI = cast<StoreInst>(User); + assert(isa<ConstantPointerNull>(SI->getOperand(0)) && + "Unexpected heap-sra user!"); + + // Insert a store of null into each global. + for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) { + Type *ValTy = cast<GlobalValue>(FieldGlobals[i])->getValueType(); + Constant *Null = Constant::getNullValue(ValTy); + new StoreInst(Null, FieldGlobals[i], SI); + } + // Erase the original store. + SI->eraseFromParent(); + } + + // While we have PHIs that are interesting to rewrite, do it. + while (!PHIsToRewrite.empty()) { + PHINode *PN = PHIsToRewrite.back().first; + unsigned FieldNo = PHIsToRewrite.back().second; + PHIsToRewrite.pop_back(); + PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]); + assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi"); + + // Add all the incoming values. This can materialize more phis. + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *InVal = PN->getIncomingValue(i); + InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues, + PHIsToRewrite); + FieldPN->addIncoming(InVal, PN->getIncomingBlock(i)); + } + } + + // Drop all inter-phi links and any loads that made it this far. + for (DenseMap<Value *, std::vector<Value *>>::iterator + I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); + I != E; ++I) { + if (PHINode *PN = dyn_cast<PHINode>(I->first)) + PN->dropAllReferences(); + else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) + LI->dropAllReferences(); + } + + // Delete all the phis and loads now that inter-references are dead. + for (DenseMap<Value *, std::vector<Value *>>::iterator + I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end(); + I != E; ++I) { + if (PHINode *PN = dyn_cast<PHINode>(I->first)) + PN->eraseFromParent(); + else if (LoadInst *LI = dyn_cast<LoadInst>(I->first)) + LI->eraseFromParent(); + } + + // The old global is now dead, remove it. + GV->eraseFromParent(); + + ++NumHeapSRA; + return cast<GlobalVariable>(FieldGlobals[0]); +} + +/// This function is called when we see a pointer global variable with a single +/// value stored it that is a malloc or cast of malloc. +static bool tryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV, CallInst *CI, + Type *AllocTy, + AtomicOrdering Ordering, + const DataLayout &DL, + TargetLibraryInfo *TLI) { + // If this is a malloc of an abstract type, don't touch it. + if (!AllocTy->isSized()) + return false; + + // We can't optimize this global unless all uses of it are *known* to be + // of the malloc value, not of the null initializer value (consider a use + // that compares the global's value against zero to see if the malloc has + // been reached). To do this, we check to see if all uses of the global + // would trap if the global were null: this proves that they must all + // happen after the malloc. + if (!AllUsesOfLoadedValueWillTrapIfNull(GV)) + return false; + + // We can't optimize this if the malloc itself is used in a complex way, + // for example, being stored into multiple globals. This allows the + // malloc to be stored into the specified global, loaded icmp'd, and + // GEP'd. These are all things we could transform to using the global + // for. + SmallPtrSet<const PHINode*, 8> PHIs; + if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs)) + return false; + + // If we have a global that is only initialized with a fixed size malloc, + // transform the program to use global memory instead of malloc'd memory. + // This eliminates dynamic allocation, avoids an indirection accessing the + // data, and exposes the resultant global to further GlobalOpt. + // We cannot optimize the malloc if we cannot determine malloc array size. + Value *NElems = getMallocArraySize(CI, DL, TLI, true); + if (!NElems) + return false; + + if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems)) + // Restrict this transformation to only working on small allocations + // (2048 bytes currently), as we don't want to introduce a 16M global or + // something. + if (NElements->getZExtValue() * DL.getTypeAllocSize(AllocTy) < 2048) { + OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, DL, TLI); + return true; + } + + // If the allocation is an array of structures, consider transforming this + // into multiple malloc'd arrays, one for each field. This is basically + // SRoA for malloc'd memory. + + if (Ordering != AtomicOrdering::NotAtomic) + return false; + + // If this is an allocation of a fixed size array of structs, analyze as a + // variable size array. malloc [100 x struct],1 -> malloc struct, 100 + if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1)) + if (ArrayType *AT = dyn_cast<ArrayType>(AllocTy)) + AllocTy = AT->getElementType(); + + StructType *AllocSTy = dyn_cast<StructType>(AllocTy); + if (!AllocSTy) + return false; + + // This the structure has an unreasonable number of fields, leave it + // alone. + if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 && + AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) { + + // If this is a fixed size array, transform the Malloc to be an alloc of + // structs. malloc [100 x struct],1 -> malloc struct, 100 + if (ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI, TLI))) { + Type *IntPtrTy = DL.getIntPtrType(CI->getType()); + unsigned TypeSize = DL.getStructLayout(AllocSTy)->getSizeInBytes(); + Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize); + Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements()); + SmallVector<OperandBundleDef, 1> OpBundles; + CI->getOperandBundlesAsDefs(OpBundles); + Instruction *Malloc = + CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy, AllocSize, NumElements, + OpBundles, nullptr, CI->getName()); + Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI); + CI->replaceAllUsesWith(Cast); + CI->eraseFromParent(); + if (BitCastInst *BCI = dyn_cast<BitCastInst>(Malloc)) + CI = cast<CallInst>(BCI->getOperand(0)); + else + CI = cast<CallInst>(Malloc); + } + + PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, DL, TLI, true), DL, + TLI); + return true; + } + + return false; +} + +// Try to optimize globals based on the knowledge that only one value (besides +// its initializer) is ever stored to the global. +static bool +optimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal, + AtomicOrdering Ordering, const DataLayout &DL, + function_ref<TargetLibraryInfo &(Function &)> GetTLI) { + // Ignore no-op GEPs and bitcasts. + StoredOnceVal = StoredOnceVal->stripPointerCasts(); + + // If we are dealing with a pointer global that is initialized to null and + // only has one (non-null) value stored into it, then we can optimize any + // users of the loaded value (often calls and loads) that would trap if the + // value was null. + if (GV->getInitializer()->getType()->isPointerTy() && + GV->getInitializer()->isNullValue() && + !NullPointerIsDefined( + nullptr /* F */, + GV->getInitializer()->getType()->getPointerAddressSpace())) { + if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) { + if (GV->getInitializer()->getType() != SOVC->getType()) + SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType()); + + // Optimize away any trapping uses of the loaded value. + if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC, DL, GetTLI)) + return true; + } else if (CallInst *CI = extractMallocCall(StoredOnceVal, GetTLI)) { + auto *TLI = &GetTLI(*CI->getFunction()); + Type *MallocType = getMallocAllocatedType(CI, TLI); + if (MallocType && tryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType, + Ordering, DL, TLI)) + return true; + } + } + + return false; +} + +/// At this point, we have learned that the only two values ever stored into GV +/// are its initializer and OtherVal. See if we can shrink the global into a +/// boolean and select between the two values whenever it is used. This exposes +/// the values to other scalar optimizations. +static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { + Type *GVElType = GV->getValueType(); + + // If GVElType is already i1, it is already shrunk. If the type of the GV is + // an FP value, pointer or vector, don't do this optimization because a select + // between them is very expensive and unlikely to lead to later + // simplification. In these cases, we typically end up with "cond ? v1 : v2" + // where v1 and v2 both require constant pool loads, a big loss. + if (GVElType == Type::getInt1Ty(GV->getContext()) || + GVElType->isFloatingPointTy() || + GVElType->isPointerTy() || GVElType->isVectorTy()) + return false; + + // Walk the use list of the global seeing if all the uses are load or store. + // If there is anything else, bail out. + for (User *U : GV->users()) + if (!isa<LoadInst>(U) && !isa<StoreInst>(U)) + return false; + + LLVM_DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV << "\n"); + + // Create the new global, initializing it to false. + GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()), + false, + GlobalValue::InternalLinkage, + ConstantInt::getFalse(GV->getContext()), + GV->getName()+".b", + GV->getThreadLocalMode(), + GV->getType()->getAddressSpace()); + NewGV->copyAttributesFrom(GV); + GV->getParent()->getGlobalList().insert(GV->getIterator(), NewGV); + + Constant *InitVal = GV->getInitializer(); + assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) && + "No reason to shrink to bool!"); + + SmallVector<DIGlobalVariableExpression *, 1> GVs; + GV->getDebugInfo(GVs); + + // If initialized to zero and storing one into the global, we can use a cast + // instead of a select to synthesize the desired value. + bool IsOneZero = false; + bool EmitOneOrZero = true; + auto *CI = dyn_cast<ConstantInt>(OtherVal); + if (CI && CI->getValue().getActiveBits() <= 64) { + IsOneZero = InitVal->isNullValue() && CI->isOne(); + + auto *CIInit = dyn_cast<ConstantInt>(GV->getInitializer()); + if (CIInit && CIInit->getValue().getActiveBits() <= 64) { + uint64_t ValInit = CIInit->getZExtValue(); + uint64_t ValOther = CI->getZExtValue(); + uint64_t ValMinus = ValOther - ValInit; + + for(auto *GVe : GVs){ + DIGlobalVariable *DGV = GVe->getVariable(); + DIExpression *E = GVe->getExpression(); + const DataLayout &DL = GV->getParent()->getDataLayout(); + unsigned SizeInOctets = + DL.getTypeAllocSizeInBits(NewGV->getType()->getElementType()) / 8; + + // It is expected that the address of global optimized variable is on + // top of the stack. After optimization, value of that variable will + // be ether 0 for initial value or 1 for other value. The following + // expression should return constant integer value depending on the + // value at global object address: + // val * (ValOther - ValInit) + ValInit: + // DW_OP_deref DW_OP_constu <ValMinus> + // DW_OP_mul DW_OP_constu <ValInit> DW_OP_plus DW_OP_stack_value + SmallVector<uint64_t, 12> Ops = { + dwarf::DW_OP_deref_size, SizeInOctets, + dwarf::DW_OP_constu, ValMinus, + dwarf::DW_OP_mul, dwarf::DW_OP_constu, ValInit, + dwarf::DW_OP_plus}; + bool WithStackValue = true; + E = DIExpression::prependOpcodes(E, Ops, WithStackValue); + DIGlobalVariableExpression *DGVE = + DIGlobalVariableExpression::get(NewGV->getContext(), DGV, E); + NewGV->addDebugInfo(DGVE); + } + EmitOneOrZero = false; + } + } + + if (EmitOneOrZero) { + // FIXME: This will only emit address for debugger on which will + // be written only 0 or 1. + for(auto *GV : GVs) + NewGV->addDebugInfo(GV); + } + + while (!GV->use_empty()) { + Instruction *UI = cast<Instruction>(GV->user_back()); + if (StoreInst *SI = dyn_cast<StoreInst>(UI)) { + // Change the store into a boolean store. + bool StoringOther = SI->getOperand(0) == OtherVal; + // Only do this if we weren't storing a loaded value. + Value *StoreVal; + if (StoringOther || SI->getOperand(0) == InitVal) { + StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()), + StoringOther); + } else { + // Otherwise, we are storing a previously loaded copy. To do this, + // change the copy from copying the original value to just copying the + // bool. + Instruction *StoredVal = cast<Instruction>(SI->getOperand(0)); + + // If we've already replaced the input, StoredVal will be a cast or + // select instruction. If not, it will be a load of the original + // global. + if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) { + assert(LI->getOperand(0) == GV && "Not a copy!"); + // Insert a new load, to preserve the saved value. + StoreVal = new LoadInst(NewGV->getValueType(), NewGV, + LI->getName() + ".b", false, None, + LI->getOrdering(), LI->getSyncScopeID(), LI); + } else { + assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) && + "This is not a form that we understand!"); + StoreVal = StoredVal->getOperand(0); + assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!"); + } + } + StoreInst *NSI = + new StoreInst(StoreVal, NewGV, false, None, SI->getOrdering(), + SI->getSyncScopeID(), SI); + NSI->setDebugLoc(SI->getDebugLoc()); + } else { + // Change the load into a load of bool then a select. + LoadInst *LI = cast<LoadInst>(UI); + LoadInst *NLI = new LoadInst(NewGV->getValueType(), NewGV, + LI->getName() + ".b", false, None, + LI->getOrdering(), LI->getSyncScopeID(), LI); + Instruction *NSI; + if (IsOneZero) + NSI = new ZExtInst(NLI, LI->getType(), "", LI); + else + NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI); + NSI->takeName(LI); + // Since LI is split into two instructions, NLI and NSI both inherit the + // same DebugLoc + NLI->setDebugLoc(LI->getDebugLoc()); + NSI->setDebugLoc(LI->getDebugLoc()); + LI->replaceAllUsesWith(NSI); + } + UI->eraseFromParent(); + } + + // Retain the name of the old global variable. People who are debugging their + // programs may expect these variables to be named the same. + NewGV->takeName(GV); + GV->eraseFromParent(); + return true; +} + +static bool deleteIfDead( + GlobalValue &GV, SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) { + GV.removeDeadConstantUsers(); + + if (!GV.isDiscardableIfUnused() && !GV.isDeclaration()) + return false; + + if (const Comdat *C = GV.getComdat()) + if (!GV.hasLocalLinkage() && NotDiscardableComdats.count(C)) + return false; + + bool Dead; + if (auto *F = dyn_cast<Function>(&GV)) + Dead = (F->isDeclaration() && F->use_empty()) || F->isDefTriviallyDead(); + else + Dead = GV.use_empty(); + if (!Dead) + return false; + + LLVM_DEBUG(dbgs() << "GLOBAL DEAD: " << GV << "\n"); + GV.eraseFromParent(); + ++NumDeleted; + return true; +} + +static bool isPointerValueDeadOnEntryToFunction( + const Function *F, GlobalValue *GV, + function_ref<DominatorTree &(Function &)> LookupDomTree) { + // Find all uses of GV. We expect them all to be in F, and if we can't + // identify any of the uses we bail out. + // + // On each of these uses, identify if the memory that GV points to is + // used/required/live at the start of the function. If it is not, for example + // if the first thing the function does is store to the GV, the GV can + // possibly be demoted. + // + // We don't do an exhaustive search for memory operations - simply look + // through bitcasts as they're quite common and benign. + const DataLayout &DL = GV->getParent()->getDataLayout(); + SmallVector<LoadInst *, 4> Loads; + SmallVector<StoreInst *, 4> Stores; + for (auto *U : GV->users()) { + if (Operator::getOpcode(U) == Instruction::BitCast) { + for (auto *UU : U->users()) { + if (auto *LI = dyn_cast<LoadInst>(UU)) + Loads.push_back(LI); + else if (auto *SI = dyn_cast<StoreInst>(UU)) + Stores.push_back(SI); + else + return false; + } + continue; + } + + Instruction *I = dyn_cast<Instruction>(U); + if (!I) + return false; + assert(I->getParent()->getParent() == F); + + if (auto *LI = dyn_cast<LoadInst>(I)) + Loads.push_back(LI); + else if (auto *SI = dyn_cast<StoreInst>(I)) + Stores.push_back(SI); + else + return false; + } + + // We have identified all uses of GV into loads and stores. Now check if all + // of them are known not to depend on the value of the global at the function + // entry point. We do this by ensuring that every load is dominated by at + // least one store. + auto &DT = LookupDomTree(*const_cast<Function *>(F)); + + // The below check is quadratic. Check we're not going to do too many tests. + // FIXME: Even though this will always have worst-case quadratic time, we + // could put effort into minimizing the average time by putting stores that + // have been shown to dominate at least one load at the beginning of the + // Stores array, making subsequent dominance checks more likely to succeed + // early. + // + // The threshold here is fairly large because global->local demotion is a + // very powerful optimization should it fire. + const unsigned Threshold = 100; + if (Loads.size() * Stores.size() > Threshold) + return false; + + for (auto *L : Loads) { + auto *LTy = L->getType(); + if (none_of(Stores, [&](const StoreInst *S) { + auto *STy = S->getValueOperand()->getType(); + // The load is only dominated by the store if DomTree says so + // and the number of bits loaded in L is less than or equal to + // the number of bits stored in S. + return DT.dominates(S, L) && + DL.getTypeStoreSize(LTy) <= DL.getTypeStoreSize(STy); + })) + return false; + } + // All loads have known dependences inside F, so the global can be localized. + return true; +} + +/// C may have non-instruction users. Can all of those users be turned into +/// instructions? +static bool allNonInstructionUsersCanBeMadeInstructions(Constant *C) { + // We don't do this exhaustively. The most common pattern that we really need + // to care about is a constant GEP or constant bitcast - so just looking + // through one single ConstantExpr. + // + // The set of constants that this function returns true for must be able to be + // handled by makeAllConstantUsesInstructions. + for (auto *U : C->users()) { + if (isa<Instruction>(U)) + continue; + if (!isa<ConstantExpr>(U)) + // Non instruction, non-constantexpr user; cannot convert this. + return false; + for (auto *UU : U->users()) + if (!isa<Instruction>(UU)) + // A constantexpr used by another constant. We don't try and recurse any + // further but just bail out at this point. + return false; + } + + return true; +} + +/// C may have non-instruction users, and +/// allNonInstructionUsersCanBeMadeInstructions has returned true. Convert the +/// non-instruction users to instructions. +static void makeAllConstantUsesInstructions(Constant *C) { + SmallVector<ConstantExpr*,4> Users; + for (auto *U : C->users()) { + if (isa<ConstantExpr>(U)) + Users.push_back(cast<ConstantExpr>(U)); + else + // We should never get here; allNonInstructionUsersCanBeMadeInstructions + // should not have returned true for C. + assert( + isa<Instruction>(U) && + "Can't transform non-constantexpr non-instruction to instruction!"); + } + + SmallVector<Value*,4> UUsers; + for (auto *U : Users) { + UUsers.clear(); + for (auto *UU : U->users()) + UUsers.push_back(UU); + for (auto *UU : UUsers) { + Instruction *UI = cast<Instruction>(UU); + Instruction *NewU = U->getAsInstruction(); + NewU->insertBefore(UI); + UI->replaceUsesOfWith(U, NewU); + } + // We've replaced all the uses, so destroy the constant. (destroyConstant + // will update value handles and metadata.) + U->destroyConstant(); + } +} + +/// Analyze the specified global variable and optimize +/// it if possible. If we make a change, return true. +static bool +processInternalGlobal(GlobalVariable *GV, const GlobalStatus &GS, + function_ref<TargetLibraryInfo &(Function &)> GetTLI, + function_ref<DominatorTree &(Function &)> LookupDomTree) { + auto &DL = GV->getParent()->getDataLayout(); + // If this is a first class global and has only one accessing function and + // this function is non-recursive, we replace the global with a local alloca + // in this function. + // + // NOTE: It doesn't make sense to promote non-single-value types since we + // are just replacing static memory to stack memory. + // + // If the global is in different address space, don't bring it to stack. + if (!GS.HasMultipleAccessingFunctions && + GS.AccessingFunction && + GV->getValueType()->isSingleValueType() && + GV->getType()->getAddressSpace() == 0 && + !GV->isExternallyInitialized() && + allNonInstructionUsersCanBeMadeInstructions(GV) && + GS.AccessingFunction->doesNotRecurse() && + isPointerValueDeadOnEntryToFunction(GS.AccessingFunction, GV, + LookupDomTree)) { + const DataLayout &DL = GV->getParent()->getDataLayout(); + + LLVM_DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV << "\n"); + Instruction &FirstI = const_cast<Instruction&>(*GS.AccessingFunction + ->getEntryBlock().begin()); + Type *ElemTy = GV->getValueType(); + // FIXME: Pass Global's alignment when globals have alignment + AllocaInst *Alloca = new AllocaInst(ElemTy, DL.getAllocaAddrSpace(), nullptr, + GV->getName(), &FirstI); + if (!isa<UndefValue>(GV->getInitializer())) + new StoreInst(GV->getInitializer(), Alloca, &FirstI); + + makeAllConstantUsesInstructions(GV); + + GV->replaceAllUsesWith(Alloca); + GV->eraseFromParent(); + ++NumLocalized; + return true; + } + + // If the global is never loaded (but may be stored to), it is dead. + // Delete it now. + if (!GS.IsLoaded) { + LLVM_DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV << "\n"); + + bool Changed; + if (isLeakCheckerRoot(GV)) { + // Delete any constant stores to the global. + Changed = CleanupPointerRootUsers(GV, GetTLI); + } else { + // Delete any stores we can find to the global. We may not be able to + // make it completely dead though. + Changed = + CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, GetTLI); + } + + // If the global is dead now, delete it. + if (GV->use_empty()) { + GV->eraseFromParent(); + ++NumDeleted; + Changed = true; + } + return Changed; + + } + if (GS.StoredType <= GlobalStatus::InitializerStored) { + LLVM_DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n"); + + // Don't actually mark a global constant if it's atomic because atomic loads + // are implemented by a trivial cmpxchg in some edge-cases and that usually + // requires write access to the variable even if it's not actually changed. + if (GS.Ordering == AtomicOrdering::NotAtomic) + GV->setConstant(true); + + // Clean up any obviously simplifiable users now. + CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, GetTLI); + + // If the global is dead now, just nuke it. + if (GV->use_empty()) { + LLVM_DEBUG(dbgs() << " *** Marking constant allowed us to simplify " + << "all users and delete global!\n"); + GV->eraseFromParent(); + ++NumDeleted; + return true; + } + + // Fall through to the next check; see if we can optimize further. + ++NumMarked; + } + if (!GV->getInitializer()->getType()->isSingleValueType()) { + const DataLayout &DL = GV->getParent()->getDataLayout(); + if (SRAGlobal(GV, DL)) + return true; + } + if (GS.StoredType == GlobalStatus::StoredOnce && GS.StoredOnceValue) { + // If the initial value for the global was an undef value, and if only + // one other value was stored into it, we can just change the + // initializer to be the stored value, then delete all stores to the + // global. This allows us to mark it constant. + if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) + if (isa<UndefValue>(GV->getInitializer())) { + // Change the initial value here. + GV->setInitializer(SOVConstant); + + // Clean up any obviously simplifiable users now. + CleanupConstantGlobalUsers(GV, GV->getInitializer(), DL, GetTLI); + + if (GV->use_empty()) { + LLVM_DEBUG(dbgs() << " *** Substituting initializer allowed us to " + << "simplify all users and delete global!\n"); + GV->eraseFromParent(); + ++NumDeleted; + } + ++NumSubstitute; + return true; + } + + // Try to optimize globals based on the knowledge that only one value + // (besides its initializer) is ever stored to the global. + if (optimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, DL, + GetTLI)) + return true; + + // Otherwise, if the global was not a boolean, we can shrink it to be a + // boolean. + if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) { + if (GS.Ordering == AtomicOrdering::NotAtomic) { + if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) { + ++NumShrunkToBool; + return true; + } + } + } + } + + return false; +} + +/// Analyze the specified global variable and optimize it if possible. If we +/// make a change, return true. +static bool +processGlobal(GlobalValue &GV, + function_ref<TargetLibraryInfo &(Function &)> GetTLI, + function_ref<DominatorTree &(Function &)> LookupDomTree) { + if (GV.getName().startswith("llvm.")) + return false; + + GlobalStatus GS; + + if (GlobalStatus::analyzeGlobal(&GV, GS)) + return false; + + bool Changed = false; + if (!GS.IsCompared && !GV.hasGlobalUnnamedAddr()) { + auto NewUnnamedAddr = GV.hasLocalLinkage() ? GlobalValue::UnnamedAddr::Global + : GlobalValue::UnnamedAddr::Local; + if (NewUnnamedAddr != GV.getUnnamedAddr()) { + GV.setUnnamedAddr(NewUnnamedAddr); + NumUnnamed++; + Changed = true; + } + } + + // Do more involved optimizations if the global is internal. + if (!GV.hasLocalLinkage()) + return Changed; + + auto *GVar = dyn_cast<GlobalVariable>(&GV); + if (!GVar) + return Changed; + + if (GVar->isConstant() || !GVar->hasInitializer()) + return Changed; + + return processInternalGlobal(GVar, GS, GetTLI, LookupDomTree) || Changed; +} + +/// Walk all of the direct calls of the specified function, changing them to +/// FastCC. +static void ChangeCalleesToFastCall(Function *F) { + for (User *U : F->users()) { + if (isa<BlockAddress>(U)) + continue; + CallSite CS(cast<Instruction>(U)); + CS.setCallingConv(CallingConv::Fast); + } +} + +static AttributeList StripAttr(LLVMContext &C, AttributeList Attrs, + Attribute::AttrKind A) { + unsigned AttrIndex; + if (Attrs.hasAttrSomewhere(A, &AttrIndex)) + return Attrs.removeAttribute(C, AttrIndex, A); + return Attrs; +} + +static void RemoveAttribute(Function *F, Attribute::AttrKind A) { + F->setAttributes(StripAttr(F->getContext(), F->getAttributes(), A)); + for (User *U : F->users()) { + if (isa<BlockAddress>(U)) + continue; + CallSite CS(cast<Instruction>(U)); + CS.setAttributes(StripAttr(F->getContext(), CS.getAttributes(), A)); + } +} + +/// Return true if this is a calling convention that we'd like to change. The +/// idea here is that we don't want to mess with the convention if the user +/// explicitly requested something with performance implications like coldcc, +/// GHC, or anyregcc. +static bool hasChangeableCC(Function *F) { + CallingConv::ID CC = F->getCallingConv(); + + // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc? + if (CC != CallingConv::C && CC != CallingConv::X86_ThisCall) + return false; + + // FIXME: Change CC for the whole chain of musttail calls when possible. + // + // Can't change CC of the function that either has musttail calls, or is a + // musttail callee itself + for (User *U : F->users()) { + if (isa<BlockAddress>(U)) + continue; + CallInst* CI = dyn_cast<CallInst>(U); + if (!CI) + continue; + + if (CI->isMustTailCall()) + return false; + } + + for (BasicBlock &BB : *F) + if (BB.getTerminatingMustTailCall()) + return false; + + return true; +} + +/// Return true if the block containing the call site has a BlockFrequency of +/// less than ColdCCRelFreq% of the entry block. +static bool isColdCallSite(CallSite CS, BlockFrequencyInfo &CallerBFI) { + const BranchProbability ColdProb(ColdCCRelFreq, 100); + auto CallSiteBB = CS.getInstruction()->getParent(); + auto CallSiteFreq = CallerBFI.getBlockFreq(CallSiteBB); + auto CallerEntryFreq = + CallerBFI.getBlockFreq(&(CS.getCaller()->getEntryBlock())); + return CallSiteFreq < CallerEntryFreq * ColdProb; +} + +// This function checks if the input function F is cold at all call sites. It +// also looks each call site's containing function, returning false if the +// caller function contains other non cold calls. The input vector AllCallsCold +// contains a list of functions that only have call sites in cold blocks. +static bool +isValidCandidateForColdCC(Function &F, + function_ref<BlockFrequencyInfo &(Function &)> GetBFI, + const std::vector<Function *> &AllCallsCold) { + + if (F.user_empty()) + return false; + + for (User *U : F.users()) { + if (isa<BlockAddress>(U)) + continue; + + CallSite CS(cast<Instruction>(U)); + Function *CallerFunc = CS.getInstruction()->getParent()->getParent(); + BlockFrequencyInfo &CallerBFI = GetBFI(*CallerFunc); + if (!isColdCallSite(CS, CallerBFI)) + return false; + auto It = std::find(AllCallsCold.begin(), AllCallsCold.end(), CallerFunc); + if (It == AllCallsCold.end()) + return false; + } + return true; +} + +static void changeCallSitesToColdCC(Function *F) { + for (User *U : F->users()) { + if (isa<BlockAddress>(U)) + continue; + CallSite CS(cast<Instruction>(U)); + CS.setCallingConv(CallingConv::Cold); + } +} + +// This function iterates over all the call instructions in the input Function +// and checks that all call sites are in cold blocks and are allowed to use the +// coldcc calling convention. +static bool +hasOnlyColdCalls(Function &F, + function_ref<BlockFrequencyInfo &(Function &)> GetBFI) { + for (BasicBlock &BB : F) { + for (Instruction &I : BB) { + if (CallInst *CI = dyn_cast<CallInst>(&I)) { + CallSite CS(cast<Instruction>(CI)); + // Skip over isline asm instructions since they aren't function calls. + if (CI->isInlineAsm()) + continue; + Function *CalledFn = CI->getCalledFunction(); + if (!CalledFn) + return false; + if (!CalledFn->hasLocalLinkage()) + return false; + // Skip over instrinsics since they won't remain as function calls. + if (CalledFn->getIntrinsicID() != Intrinsic::not_intrinsic) + continue; + // Check if it's valid to use coldcc calling convention. + if (!hasChangeableCC(CalledFn) || CalledFn->isVarArg() || + CalledFn->hasAddressTaken()) + return false; + BlockFrequencyInfo &CallerBFI = GetBFI(F); + if (!isColdCallSite(CS, CallerBFI)) + return false; + } + } + } + return true; +} + +static bool +OptimizeFunctions(Module &M, + function_ref<TargetLibraryInfo &(Function &)> GetTLI, + function_ref<TargetTransformInfo &(Function &)> GetTTI, + function_ref<BlockFrequencyInfo &(Function &)> GetBFI, + function_ref<DominatorTree &(Function &)> LookupDomTree, + SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) { + + bool Changed = false; + + std::vector<Function *> AllCallsCold; + for (Module::iterator FI = M.begin(), E = M.end(); FI != E;) { + Function *F = &*FI++; + if (hasOnlyColdCalls(*F, GetBFI)) + AllCallsCold.push_back(F); + } + + // Optimize functions. + for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) { + Function *F = &*FI++; + + // Don't perform global opt pass on naked functions; we don't want fast + // calling conventions for naked functions. + if (F->hasFnAttribute(Attribute::Naked)) + continue; + + // Functions without names cannot be referenced outside this module. + if (!F->hasName() && !F->isDeclaration() && !F->hasLocalLinkage()) + F->setLinkage(GlobalValue::InternalLinkage); + + if (deleteIfDead(*F, NotDiscardableComdats)) { + Changed = true; + continue; + } + + // LLVM's definition of dominance allows instructions that are cyclic + // in unreachable blocks, e.g.: + // %pat = select i1 %condition, @global, i16* %pat + // because any instruction dominates an instruction in a block that's + // not reachable from entry. + // So, remove unreachable blocks from the function, because a) there's + // no point in analyzing them and b) GlobalOpt should otherwise grow + // some more complicated logic to break these cycles. + if (!F->isDeclaration()) { + auto &DT = LookupDomTree(*F); + DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); + Changed |= removeUnreachableBlocks(*F, &DTU); + } + + Changed |= processGlobal(*F, GetTLI, LookupDomTree); + + if (!F->hasLocalLinkage()) + continue; + + // If we have an inalloca parameter that we can safely remove the + // inalloca attribute from, do so. This unlocks optimizations that + // wouldn't be safe in the presence of inalloca. + // FIXME: We should also hoist alloca affected by this to the entry + // block if possible. + if (F->getAttributes().hasAttrSomewhere(Attribute::InAlloca) && + !F->hasAddressTaken()) { + RemoveAttribute(F, Attribute::InAlloca); + Changed = true; + } + + if (hasChangeableCC(F) && !F->isVarArg() && !F->hasAddressTaken()) { + NumInternalFunc++; + TargetTransformInfo &TTI = GetTTI(*F); + // Change the calling convention to coldcc if either stress testing is + // enabled or the target would like to use coldcc on functions which are + // cold at all call sites and the callers contain no other non coldcc + // calls. + if (EnableColdCCStressTest || + (TTI.useColdCCForColdCall(*F) && + isValidCandidateForColdCC(*F, GetBFI, AllCallsCold))) { + F->setCallingConv(CallingConv::Cold); + changeCallSitesToColdCC(F); + Changed = true; + NumColdCC++; + } + } + + if (hasChangeableCC(F) && !F->isVarArg() && + !F->hasAddressTaken()) { + // If this function has a calling convention worth changing, is not a + // varargs function, and is only called directly, promote it to use the + // Fast calling convention. + F->setCallingConv(CallingConv::Fast); + ChangeCalleesToFastCall(F); + ++NumFastCallFns; + Changed = true; + } + + if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) && + !F->hasAddressTaken()) { + // The function is not used by a trampoline intrinsic, so it is safe + // to remove the 'nest' attribute. + RemoveAttribute(F, Attribute::Nest); + ++NumNestRemoved; + Changed = true; + } + } + return Changed; +} + +static bool +OptimizeGlobalVars(Module &M, + function_ref<TargetLibraryInfo &(Function &)> GetTLI, + function_ref<DominatorTree &(Function &)> LookupDomTree, + SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) { + bool Changed = false; + + for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); + GVI != E; ) { + GlobalVariable *GV = &*GVI++; + // Global variables without names cannot be referenced outside this module. + if (!GV->hasName() && !GV->isDeclaration() && !GV->hasLocalLinkage()) + GV->setLinkage(GlobalValue::InternalLinkage); + // Simplify the initializer. + if (GV->hasInitializer()) + if (auto *C = dyn_cast<Constant>(GV->getInitializer())) { + auto &DL = M.getDataLayout(); + // TLI is not used in the case of a Constant, so use default nullptr + // for that optional parameter, since we don't have a Function to + // provide GetTLI anyway. + Constant *New = ConstantFoldConstant(C, DL, /*TLI*/ nullptr); + if (New && New != C) + GV->setInitializer(New); + } + + if (deleteIfDead(*GV, NotDiscardableComdats)) { + Changed = true; + continue; + } + + Changed |= processGlobal(*GV, GetTLI, LookupDomTree); + } + return Changed; +} + +/// Evaluate a piece of a constantexpr store into a global initializer. This +/// returns 'Init' modified to reflect 'Val' stored into it. At this point, the +/// GEP operands of Addr [0, OpNo) have been stepped into. +static Constant *EvaluateStoreInto(Constant *Init, Constant *Val, + ConstantExpr *Addr, unsigned OpNo) { + // Base case of the recursion. + if (OpNo == Addr->getNumOperands()) { + assert(Val->getType() == Init->getType() && "Type mismatch!"); + return Val; + } + + SmallVector<Constant*, 32> Elts; + if (StructType *STy = dyn_cast<StructType>(Init->getType())) { + // Break up the constant into its elements. + for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) + Elts.push_back(Init->getAggregateElement(i)); + + // Replace the element that we are supposed to. + ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo)); + unsigned Idx = CU->getZExtValue(); + assert(Idx < STy->getNumElements() && "Struct index out of range!"); + Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1); + + // Return the modified struct. + return ConstantStruct::get(STy, Elts); + } + + ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo)); + SequentialType *InitTy = cast<SequentialType>(Init->getType()); + uint64_t NumElts = InitTy->getNumElements(); + + // Break up the array into elements. + for (uint64_t i = 0, e = NumElts; i != e; ++i) + Elts.push_back(Init->getAggregateElement(i)); + + assert(CI->getZExtValue() < NumElts); + Elts[CI->getZExtValue()] = + EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1); + + if (Init->getType()->isArrayTy()) + return ConstantArray::get(cast<ArrayType>(InitTy), Elts); + return ConstantVector::get(Elts); +} + +/// We have decided that Addr (which satisfies the predicate +/// isSimpleEnoughPointerToCommit) should get Val as its value. Make it happen. +static void CommitValueTo(Constant *Val, Constant *Addr) { + if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) { + assert(GV->hasInitializer()); + GV->setInitializer(Val); + return; + } + + ConstantExpr *CE = cast<ConstantExpr>(Addr); + GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0)); + GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2)); +} + +/// Given a map of address -> value, where addresses are expected to be some form +/// of either a global or a constant GEP, set the initializer for the address to +/// be the value. This performs mostly the same function as CommitValueTo() +/// and EvaluateStoreInto() but is optimized to be more efficient for the common +/// case where the set of addresses are GEPs sharing the same underlying global, +/// processing the GEPs in batches rather than individually. +/// +/// To give an example, consider the following C++ code adapted from the clang +/// regression tests: +/// struct S { +/// int n = 10; +/// int m = 2 * n; +/// S(int a) : n(a) {} +/// }; +/// +/// template<typename T> +/// struct U { +/// T *r = &q; +/// T q = 42; +/// U *p = this; +/// }; +/// +/// U<S> e; +/// +/// The global static constructor for 'e' will need to initialize 'r' and 'p' of +/// the outer struct, while also initializing the inner 'q' structs 'n' and 'm' +/// members. This batch algorithm will simply use general CommitValueTo() method +/// to handle the complex nested S struct initialization of 'q', before +/// processing the outermost members in a single batch. Using CommitValueTo() to +/// handle member in the outer struct is inefficient when the struct/array is +/// very large as we end up creating and destroy constant arrays for each +/// initialization. +/// For the above case, we expect the following IR to be generated: +/// +/// %struct.U = type { %struct.S*, %struct.S, %struct.U* } +/// %struct.S = type { i32, i32 } +/// @e = global %struct.U { %struct.S* gep inbounds (%struct.U, %struct.U* @e, +/// i64 0, i32 1), +/// %struct.S { i32 42, i32 84 }, %struct.U* @e } +/// The %struct.S { i32 42, i32 84 } inner initializer is treated as a complex +/// constant expression, while the other two elements of @e are "simple". +static void BatchCommitValueTo(const DenseMap<Constant*, Constant*> &Mem) { + SmallVector<std::pair<GlobalVariable*, Constant*>, 32> GVs; + SmallVector<std::pair<ConstantExpr*, Constant*>, 32> ComplexCEs; + SmallVector<std::pair<ConstantExpr*, Constant*>, 32> SimpleCEs; + SimpleCEs.reserve(Mem.size()); + + for (const auto &I : Mem) { + if (auto *GV = dyn_cast<GlobalVariable>(I.first)) { + GVs.push_back(std::make_pair(GV, I.second)); + } else { + ConstantExpr *GEP = cast<ConstantExpr>(I.first); + // We don't handle the deeply recursive case using the batch method. + if (GEP->getNumOperands() > 3) + ComplexCEs.push_back(std::make_pair(GEP, I.second)); + else + SimpleCEs.push_back(std::make_pair(GEP, I.second)); + } + } + + // The algorithm below doesn't handle cases like nested structs, so use the + // slower fully general method if we have to. + for (auto ComplexCE : ComplexCEs) + CommitValueTo(ComplexCE.second, ComplexCE.first); + + for (auto GVPair : GVs) { + assert(GVPair.first->hasInitializer()); + GVPair.first->setInitializer(GVPair.second); + } + + if (SimpleCEs.empty()) + return; + + // We cache a single global's initializer elements in the case where the + // subsequent address/val pair uses the same one. This avoids throwing away and + // rebuilding the constant struct/vector/array just because one element is + // modified at a time. + SmallVector<Constant *, 32> Elts; + Elts.reserve(SimpleCEs.size()); + GlobalVariable *CurrentGV = nullptr; + + auto commitAndSetupCache = [&](GlobalVariable *GV, bool Update) { + Constant *Init = GV->getInitializer(); + Type *Ty = Init->getType(); + if (Update) { + if (CurrentGV) { + assert(CurrentGV && "Expected a GV to commit to!"); + Type *CurrentInitTy = CurrentGV->getInitializer()->getType(); + // We have a valid cache that needs to be committed. + if (StructType *STy = dyn_cast<StructType>(CurrentInitTy)) + CurrentGV->setInitializer(ConstantStruct::get(STy, Elts)); + else if (ArrayType *ArrTy = dyn_cast<ArrayType>(CurrentInitTy)) + CurrentGV->setInitializer(ConstantArray::get(ArrTy, Elts)); + else + CurrentGV->setInitializer(ConstantVector::get(Elts)); + } + if (CurrentGV == GV) + return; + // Need to clear and set up cache for new initializer. + CurrentGV = GV; + Elts.clear(); + unsigned NumElts; + if (auto *STy = dyn_cast<StructType>(Ty)) + NumElts = STy->getNumElements(); + else + NumElts = cast<SequentialType>(Ty)->getNumElements(); + for (unsigned i = 0, e = NumElts; i != e; ++i) + Elts.push_back(Init->getAggregateElement(i)); + } + }; + + for (auto CEPair : SimpleCEs) { + ConstantExpr *GEP = CEPair.first; + Constant *Val = CEPair.second; + + GlobalVariable *GV = cast<GlobalVariable>(GEP->getOperand(0)); + commitAndSetupCache(GV, GV != CurrentGV); + ConstantInt *CI = cast<ConstantInt>(GEP->getOperand(2)); + Elts[CI->getZExtValue()] = Val; + } + // The last initializer in the list needs to be committed, others + // will be committed on a new initializer being processed. + commitAndSetupCache(CurrentGV, true); +} + +/// Evaluate static constructors in the function, if we can. Return true if we +/// can, false otherwise. +static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL, + TargetLibraryInfo *TLI) { + // Call the function. + Evaluator Eval(DL, TLI); + Constant *RetValDummy; + bool EvalSuccess = Eval.EvaluateFunction(F, RetValDummy, + SmallVector<Constant*, 0>()); + + if (EvalSuccess) { + ++NumCtorsEvaluated; + + // We succeeded at evaluation: commit the result. + LLVM_DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '" + << F->getName() << "' to " + << Eval.getMutatedMemory().size() << " stores.\n"); + BatchCommitValueTo(Eval.getMutatedMemory()); + for (GlobalVariable *GV : Eval.getInvariants()) + GV->setConstant(true); + } + + return EvalSuccess; +} + +static int compareNames(Constant *const *A, Constant *const *B) { + Value *AStripped = (*A)->stripPointerCasts(); + Value *BStripped = (*B)->stripPointerCasts(); + return AStripped->getName().compare(BStripped->getName()); +} + +static void setUsedInitializer(GlobalVariable &V, + const SmallPtrSetImpl<GlobalValue *> &Init) { + if (Init.empty()) { + V.eraseFromParent(); + return; + } + + // Type of pointer to the array of pointers. + PointerType *Int8PtrTy = Type::getInt8PtrTy(V.getContext(), 0); + + SmallVector<Constant *, 8> UsedArray; + for (GlobalValue *GV : Init) { + Constant *Cast + = ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, Int8PtrTy); + UsedArray.push_back(Cast); + } + // Sort to get deterministic order. + array_pod_sort(UsedArray.begin(), UsedArray.end(), compareNames); + ArrayType *ATy = ArrayType::get(Int8PtrTy, UsedArray.size()); + + Module *M = V.getParent(); + V.removeFromParent(); + GlobalVariable *NV = + new GlobalVariable(*M, ATy, false, GlobalValue::AppendingLinkage, + ConstantArray::get(ATy, UsedArray), ""); + NV->takeName(&V); + NV->setSection("llvm.metadata"); + delete &V; +} + +namespace { + +/// An easy to access representation of llvm.used and llvm.compiler.used. +class LLVMUsed { + SmallPtrSet<GlobalValue *, 8> Used; + SmallPtrSet<GlobalValue *, 8> CompilerUsed; + GlobalVariable *UsedV; + GlobalVariable *CompilerUsedV; + +public: + LLVMUsed(Module &M) { + UsedV = collectUsedGlobalVariables(M, Used, false); + CompilerUsedV = collectUsedGlobalVariables(M, CompilerUsed, true); + } + + using iterator = SmallPtrSet<GlobalValue *, 8>::iterator; + using used_iterator_range = iterator_range<iterator>; + + iterator usedBegin() { return Used.begin(); } + iterator usedEnd() { return Used.end(); } + + used_iterator_range used() { + return used_iterator_range(usedBegin(), usedEnd()); + } + + iterator compilerUsedBegin() { return CompilerUsed.begin(); } + iterator compilerUsedEnd() { return CompilerUsed.end(); } + + used_iterator_range compilerUsed() { + return used_iterator_range(compilerUsedBegin(), compilerUsedEnd()); + } + + bool usedCount(GlobalValue *GV) const { return Used.count(GV); } + + bool compilerUsedCount(GlobalValue *GV) const { + return CompilerUsed.count(GV); + } + + bool usedErase(GlobalValue *GV) { return Used.erase(GV); } + bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(GV); } + bool usedInsert(GlobalValue *GV) { return Used.insert(GV).second; } + + bool compilerUsedInsert(GlobalValue *GV) { + return CompilerUsed.insert(GV).second; + } + + void syncVariablesAndSets() { + if (UsedV) + setUsedInitializer(*UsedV, Used); + if (CompilerUsedV) + setUsedInitializer(*CompilerUsedV, CompilerUsed); + } +}; + +} // end anonymous namespace + +static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) { + if (GA.use_empty()) // No use at all. + return false; + + assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) && + "We should have removed the duplicated " + "element from llvm.compiler.used"); + if (!GA.hasOneUse()) + // Strictly more than one use. So at least one is not in llvm.used and + // llvm.compiler.used. + return true; + + // Exactly one use. Check if it is in llvm.used or llvm.compiler.used. + return !U.usedCount(&GA) && !U.compilerUsedCount(&GA); +} + +static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V, + const LLVMUsed &U) { + unsigned N = 2; + assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) && + "We should have removed the duplicated " + "element from llvm.compiler.used"); + if (U.usedCount(&V) || U.compilerUsedCount(&V)) + ++N; + return V.hasNUsesOrMore(N); +} + +static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) { + if (!GA.hasLocalLinkage()) + return true; + + return U.usedCount(&GA) || U.compilerUsedCount(&GA); +} + +static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U, + bool &RenameTarget) { + RenameTarget = false; + bool Ret = false; + if (hasUseOtherThanLLVMUsed(GA, U)) + Ret = true; + + // If the alias is externally visible, we may still be able to simplify it. + if (!mayHaveOtherReferences(GA, U)) + return Ret; + + // If the aliasee has internal linkage, give it the name and linkage + // of the alias, and delete the alias. This turns: + // define internal ... @f(...) + // @a = alias ... @f + // into: + // define ... @a(...) + Constant *Aliasee = GA.getAliasee(); + GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts()); + if (!Target->hasLocalLinkage()) + return Ret; + + // Do not perform the transform if multiple aliases potentially target the + // aliasee. This check also ensures that it is safe to replace the section + // and other attributes of the aliasee with those of the alias. + if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U)) + return Ret; + + RenameTarget = true; + return true; +} + +static bool +OptimizeGlobalAliases(Module &M, + SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) { + bool Changed = false; + LLVMUsed Used(M); + + for (GlobalValue *GV : Used.used()) + Used.compilerUsedErase(GV); + + for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); + I != E;) { + GlobalAlias *J = &*I++; + + // Aliases without names cannot be referenced outside this module. + if (!J->hasName() && !J->isDeclaration() && !J->hasLocalLinkage()) + J->setLinkage(GlobalValue::InternalLinkage); + + if (deleteIfDead(*J, NotDiscardableComdats)) { + Changed = true; + continue; + } + + // If the alias can change at link time, nothing can be done - bail out. + if (J->isInterposable()) + continue; + + Constant *Aliasee = J->getAliasee(); + GlobalValue *Target = dyn_cast<GlobalValue>(Aliasee->stripPointerCasts()); + // We can't trivially replace the alias with the aliasee if the aliasee is + // non-trivial in some way. + // TODO: Try to handle non-zero GEPs of local aliasees. + if (!Target) + continue; + Target->removeDeadConstantUsers(); + + // Make all users of the alias use the aliasee instead. + bool RenameTarget; + if (!hasUsesToReplace(*J, Used, RenameTarget)) + continue; + + J->replaceAllUsesWith(ConstantExpr::getBitCast(Aliasee, J->getType())); + ++NumAliasesResolved; + Changed = true; + + if (RenameTarget) { + // Give the aliasee the name, linkage and other attributes of the alias. + Target->takeName(&*J); + Target->setLinkage(J->getLinkage()); + Target->setDSOLocal(J->isDSOLocal()); + Target->setVisibility(J->getVisibility()); + Target->setDLLStorageClass(J->getDLLStorageClass()); + + if (Used.usedErase(&*J)) + Used.usedInsert(Target); + + if (Used.compilerUsedErase(&*J)) + Used.compilerUsedInsert(Target); + } else if (mayHaveOtherReferences(*J, Used)) + continue; + + // Delete the alias. + M.getAliasList().erase(J); + ++NumAliasesRemoved; + Changed = true; + } + + Used.syncVariablesAndSets(); + + return Changed; +} + +static Function * +FindCXAAtExit(Module &M, function_ref<TargetLibraryInfo &(Function &)> GetTLI) { + // Hack to get a default TLI before we have actual Function. + auto FuncIter = M.begin(); + if (FuncIter == M.end()) + return nullptr; + auto *TLI = &GetTLI(*FuncIter); + + LibFunc F = LibFunc_cxa_atexit; + if (!TLI->has(F)) + return nullptr; + + Function *Fn = M.getFunction(TLI->getName(F)); + if (!Fn) + return nullptr; + + // Now get the actual TLI for Fn. + TLI = &GetTLI(*Fn); + + // Make sure that the function has the correct prototype. + if (!TLI->getLibFunc(*Fn, F) || F != LibFunc_cxa_atexit) + return nullptr; + + return Fn; +} + +/// Returns whether the given function is an empty C++ destructor and can +/// therefore be eliminated. +/// Note that we assume that other optimization passes have already simplified +/// the code so we simply check for 'ret'. +static bool cxxDtorIsEmpty(const Function &Fn) { + // FIXME: We could eliminate C++ destructors if they're readonly/readnone and + // nounwind, but that doesn't seem worth doing. + if (Fn.isDeclaration()) + return false; + + for (auto &I : Fn.getEntryBlock()) { + if (isa<DbgInfoIntrinsic>(I)) + continue; + if (isa<ReturnInst>(I)) + return true; + break; + } + return false; +} + +static bool OptimizeEmptyGlobalCXXDtors(Function *CXAAtExitFn) { + /// Itanium C++ ABI p3.3.5: + /// + /// After constructing a global (or local static) object, that will require + /// destruction on exit, a termination function is registered as follows: + /// + /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d ); + /// + /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the + /// call f(p) when DSO d is unloaded, before all such termination calls + /// registered before this one. It returns zero if registration is + /// successful, nonzero on failure. + + // This pass will look for calls to __cxa_atexit where the function is trivial + // and remove them. + bool Changed = false; + + for (auto I = CXAAtExitFn->user_begin(), E = CXAAtExitFn->user_end(); + I != E;) { + // We're only interested in calls. Theoretically, we could handle invoke + // instructions as well, but neither llvm-gcc nor clang generate invokes + // to __cxa_atexit. + CallInst *CI = dyn_cast<CallInst>(*I++); + if (!CI) + continue; + + Function *DtorFn = + dyn_cast<Function>(CI->getArgOperand(0)->stripPointerCasts()); + if (!DtorFn || !cxxDtorIsEmpty(*DtorFn)) + continue; + + // Just remove the call. + CI->replaceAllUsesWith(Constant::getNullValue(CI->getType())); + CI->eraseFromParent(); + + ++NumCXXDtorsRemoved; + + Changed |= true; + } + + return Changed; +} + +static bool optimizeGlobalsInModule( + Module &M, const DataLayout &DL, + function_ref<TargetLibraryInfo &(Function &)> GetTLI, + function_ref<TargetTransformInfo &(Function &)> GetTTI, + function_ref<BlockFrequencyInfo &(Function &)> GetBFI, + function_ref<DominatorTree &(Function &)> LookupDomTree) { + SmallPtrSet<const Comdat *, 8> NotDiscardableComdats; + bool Changed = false; + bool LocalChange = true; + while (LocalChange) { + LocalChange = false; + + NotDiscardableComdats.clear(); + for (const GlobalVariable &GV : M.globals()) + if (const Comdat *C = GV.getComdat()) + if (!GV.isDiscardableIfUnused() || !GV.use_empty()) + NotDiscardableComdats.insert(C); + for (Function &F : M) + if (const Comdat *C = F.getComdat()) + if (!F.isDefTriviallyDead()) + NotDiscardableComdats.insert(C); + for (GlobalAlias &GA : M.aliases()) + if (const Comdat *C = GA.getComdat()) + if (!GA.isDiscardableIfUnused() || !GA.use_empty()) + NotDiscardableComdats.insert(C); + + // Delete functions that are trivially dead, ccc -> fastcc + LocalChange |= OptimizeFunctions(M, GetTLI, GetTTI, GetBFI, LookupDomTree, + NotDiscardableComdats); + + // Optimize global_ctors list. + LocalChange |= optimizeGlobalCtorsList(M, [&](Function *F) { + return EvaluateStaticConstructor(F, DL, &GetTLI(*F)); + }); + + // Optimize non-address-taken globals. + LocalChange |= + OptimizeGlobalVars(M, GetTLI, LookupDomTree, NotDiscardableComdats); + + // Resolve aliases, when possible. + LocalChange |= OptimizeGlobalAliases(M, NotDiscardableComdats); + + // Try to remove trivial global destructors if they are not removed + // already. + Function *CXAAtExitFn = FindCXAAtExit(M, GetTLI); + if (CXAAtExitFn) + LocalChange |= OptimizeEmptyGlobalCXXDtors(CXAAtExitFn); + + Changed |= LocalChange; + } + + // TODO: Move all global ctors functions to the end of the module for code + // layout. + + return Changed; +} + +PreservedAnalyses GlobalOptPass::run(Module &M, ModuleAnalysisManager &AM) { + auto &DL = M.getDataLayout(); + auto &FAM = + AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager(); + auto LookupDomTree = [&FAM](Function &F) -> DominatorTree &{ + return FAM.getResult<DominatorTreeAnalysis>(F); + }; + auto GetTLI = [&FAM](Function &F) -> TargetLibraryInfo & { + return FAM.getResult<TargetLibraryAnalysis>(F); + }; + auto GetTTI = [&FAM](Function &F) -> TargetTransformInfo & { + return FAM.getResult<TargetIRAnalysis>(F); + }; + + auto GetBFI = [&FAM](Function &F) -> BlockFrequencyInfo & { + return FAM.getResult<BlockFrequencyAnalysis>(F); + }; + + if (!optimizeGlobalsInModule(M, DL, GetTLI, GetTTI, GetBFI, LookupDomTree)) + return PreservedAnalyses::all(); + return PreservedAnalyses::none(); +} + +namespace { + +struct GlobalOptLegacyPass : public ModulePass { + static char ID; // Pass identification, replacement for typeid + + GlobalOptLegacyPass() : ModulePass(ID) { + initializeGlobalOptLegacyPassPass(*PassRegistry::getPassRegistry()); + } + + bool runOnModule(Module &M) override { + if (skipModule(M)) + return false; + + auto &DL = M.getDataLayout(); + auto LookupDomTree = [this](Function &F) -> DominatorTree & { + return this->getAnalysis<DominatorTreeWrapperPass>(F).getDomTree(); + }; + auto GetTLI = [this](Function &F) -> TargetLibraryInfo & { + return this->getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); + }; + auto GetTTI = [this](Function &F) -> TargetTransformInfo & { + return this->getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); + }; + + auto GetBFI = [this](Function &F) -> BlockFrequencyInfo & { + return this->getAnalysis<BlockFrequencyInfoWrapperPass>(F).getBFI(); + }; + + return optimizeGlobalsInModule(M, DL, GetTLI, GetTTI, GetBFI, + LookupDomTree); + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addRequired<TargetTransformInfoWrapperPass>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequired<BlockFrequencyInfoWrapperPass>(); + } +}; + +} // end anonymous namespace + +char GlobalOptLegacyPass::ID = 0; + +INITIALIZE_PASS_BEGIN(GlobalOptLegacyPass, "globalopt", + "Global Variable Optimizer", false, false) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(BlockFrequencyInfoWrapperPass) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_END(GlobalOptLegacyPass, "globalopt", + "Global Variable Optimizer", false, false) + +ModulePass *llvm::createGlobalOptimizerPass() { + return new GlobalOptLegacyPass(); +} |