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Diffstat (limited to 'contrib/llvm-project/llvm/lib/CodeGen/MachineSink.cpp')
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diff --git a/contrib/llvm-project/llvm/lib/CodeGen/MachineSink.cpp b/contrib/llvm-project/llvm/lib/CodeGen/MachineSink.cpp new file mode 100644 index 000000000000..5f958bbc31b7 --- /dev/null +++ b/contrib/llvm-project/llvm/lib/CodeGen/MachineSink.cpp @@ -0,0 +1,1408 @@ +//===- MachineSink.cpp - Sinking for machine instructions -----------------===// +// +// 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 moves instructions into successor blocks when possible, so that +// they aren't executed on paths where their results aren't needed. +// +// This pass is not intended to be a replacement or a complete alternative +// for an LLVM-IR-level sinking pass. It is only designed to sink simple +// constructs that are not exposed before lowering and instruction selection. +// +//===----------------------------------------------------------------------===// + +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/PointerIntPair.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/SparseBitVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/CodeGen/MachineBasicBlock.h" +#include "llvm/CodeGen/MachineBlockFrequencyInfo.h" +#include "llvm/CodeGen/MachineBranchProbabilityInfo.h" +#include "llvm/CodeGen/MachineDominators.h" +#include "llvm/CodeGen/MachineFunction.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineInstr.h" +#include "llvm/CodeGen/MachineLoopInfo.h" +#include "llvm/CodeGen/MachineOperand.h" +#include "llvm/CodeGen/MachinePostDominators.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/CodeGen/TargetInstrInfo.h" +#include "llvm/CodeGen/TargetRegisterInfo.h" +#include "llvm/CodeGen/TargetSubtargetInfo.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/DebugInfoMetadata.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/InitializePasses.h" +#include "llvm/MC/MCRegisterInfo.h" +#include "llvm/Pass.h" +#include "llvm/Support/BranchProbability.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include <algorithm> +#include <cassert> +#include <cstdint> +#include <map> +#include <utility> +#include <vector> + +using namespace llvm; + +#define DEBUG_TYPE "machine-sink" + +static cl::opt<bool> +SplitEdges("machine-sink-split", + cl::desc("Split critical edges during machine sinking"), + cl::init(true), cl::Hidden); + +static cl::opt<bool> +UseBlockFreqInfo("machine-sink-bfi", + cl::desc("Use block frequency info to find successors to sink"), + cl::init(true), cl::Hidden); + +static cl::opt<unsigned> SplitEdgeProbabilityThreshold( + "machine-sink-split-probability-threshold", + cl::desc( + "Percentage threshold for splitting single-instruction critical edge. " + "If the branch threshold is higher than this threshold, we allow " + "speculative execution of up to 1 instruction to avoid branching to " + "splitted critical edge"), + cl::init(40), cl::Hidden); + +STATISTIC(NumSunk, "Number of machine instructions sunk"); +STATISTIC(NumSplit, "Number of critical edges split"); +STATISTIC(NumCoalesces, "Number of copies coalesced"); +STATISTIC(NumPostRACopySink, "Number of copies sunk after RA"); + +namespace { + + class MachineSinking : public MachineFunctionPass { + const TargetInstrInfo *TII; + const TargetRegisterInfo *TRI; + MachineRegisterInfo *MRI; // Machine register information + MachineDominatorTree *DT; // Machine dominator tree + MachinePostDominatorTree *PDT; // Machine post dominator tree + MachineLoopInfo *LI; + MachineBlockFrequencyInfo *MBFI; + const MachineBranchProbabilityInfo *MBPI; + AliasAnalysis *AA; + + // Remember which edges have been considered for breaking. + SmallSet<std::pair<MachineBasicBlock*, MachineBasicBlock*>, 8> + CEBCandidates; + // Remember which edges we are about to split. + // This is different from CEBCandidates since those edges + // will be split. + SetVector<std::pair<MachineBasicBlock *, MachineBasicBlock *>> ToSplit; + + SparseBitVector<> RegsToClearKillFlags; + + using AllSuccsCache = + std::map<MachineBasicBlock *, SmallVector<MachineBasicBlock *, 4>>; + + /// DBG_VALUE pointer and flag. The flag is true if this DBG_VALUE is + /// post-dominated by another DBG_VALUE of the same variable location. + /// This is necessary to detect sequences such as: + /// %0 = someinst + /// DBG_VALUE %0, !123, !DIExpression() + /// %1 = anotherinst + /// DBG_VALUE %1, !123, !DIExpression() + /// Where if %0 were to sink, the DBG_VAUE should not sink with it, as that + /// would re-order assignments. + using SeenDbgUser = PointerIntPair<MachineInstr *, 1>; + + /// Record of DBG_VALUE uses of vregs in a block, so that we can identify + /// debug instructions to sink. + SmallDenseMap<unsigned, TinyPtrVector<SeenDbgUser>> SeenDbgUsers; + + /// Record of debug variables that have had their locations set in the + /// current block. + DenseSet<DebugVariable> SeenDbgVars; + + public: + static char ID; // Pass identification + + MachineSinking() : MachineFunctionPass(ID) { + initializeMachineSinkingPass(*PassRegistry::getPassRegistry()); + } + + bool runOnMachineFunction(MachineFunction &MF) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + MachineFunctionPass::getAnalysisUsage(AU); + AU.addRequired<AAResultsWrapperPass>(); + AU.addRequired<MachineDominatorTree>(); + AU.addRequired<MachinePostDominatorTree>(); + AU.addRequired<MachineLoopInfo>(); + AU.addRequired<MachineBranchProbabilityInfo>(); + AU.addPreserved<MachineLoopInfo>(); + if (UseBlockFreqInfo) + AU.addRequired<MachineBlockFrequencyInfo>(); + } + + void releaseMemory() override { + CEBCandidates.clear(); + } + + private: + bool ProcessBlock(MachineBasicBlock &MBB); + void ProcessDbgInst(MachineInstr &MI); + bool isWorthBreakingCriticalEdge(MachineInstr &MI, + MachineBasicBlock *From, + MachineBasicBlock *To); + + /// Postpone the splitting of the given critical + /// edge (\p From, \p To). + /// + /// We do not split the edges on the fly. Indeed, this invalidates + /// the dominance information and thus triggers a lot of updates + /// of that information underneath. + /// Instead, we postpone all the splits after each iteration of + /// the main loop. That way, the information is at least valid + /// for the lifetime of an iteration. + /// + /// \return True if the edge is marked as toSplit, false otherwise. + /// False can be returned if, for instance, this is not profitable. + bool PostponeSplitCriticalEdge(MachineInstr &MI, + MachineBasicBlock *From, + MachineBasicBlock *To, + bool BreakPHIEdge); + bool SinkInstruction(MachineInstr &MI, bool &SawStore, + AllSuccsCache &AllSuccessors); + + /// If we sink a COPY inst, some debug users of it's destination may no + /// longer be dominated by the COPY, and will eventually be dropped. + /// This is easily rectified by forwarding the non-dominated debug uses + /// to the copy source. + void SalvageUnsunkDebugUsersOfCopy(MachineInstr &, + MachineBasicBlock *TargetBlock); + bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB, + MachineBasicBlock *DefMBB, + bool &BreakPHIEdge, bool &LocalUse) const; + MachineBasicBlock *FindSuccToSinkTo(MachineInstr &MI, MachineBasicBlock *MBB, + bool &BreakPHIEdge, AllSuccsCache &AllSuccessors); + bool isProfitableToSinkTo(unsigned Reg, MachineInstr &MI, + MachineBasicBlock *MBB, + MachineBasicBlock *SuccToSinkTo, + AllSuccsCache &AllSuccessors); + + bool PerformTrivialForwardCoalescing(MachineInstr &MI, + MachineBasicBlock *MBB); + + SmallVector<MachineBasicBlock *, 4> & + GetAllSortedSuccessors(MachineInstr &MI, MachineBasicBlock *MBB, + AllSuccsCache &AllSuccessors) const; + }; + +} // end anonymous namespace + +char MachineSinking::ID = 0; + +char &llvm::MachineSinkingID = MachineSinking::ID; + +INITIALIZE_PASS_BEGIN(MachineSinking, DEBUG_TYPE, + "Machine code sinking", false, false) +INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo) +INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) +INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo) +INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) +INITIALIZE_PASS_END(MachineSinking, DEBUG_TYPE, + "Machine code sinking", false, false) + +bool MachineSinking::PerformTrivialForwardCoalescing(MachineInstr &MI, + MachineBasicBlock *MBB) { + if (!MI.isCopy()) + return false; + + Register SrcReg = MI.getOperand(1).getReg(); + Register DstReg = MI.getOperand(0).getReg(); + if (!Register::isVirtualRegister(SrcReg) || + !Register::isVirtualRegister(DstReg) || !MRI->hasOneNonDBGUse(SrcReg)) + return false; + + const TargetRegisterClass *SRC = MRI->getRegClass(SrcReg); + const TargetRegisterClass *DRC = MRI->getRegClass(DstReg); + if (SRC != DRC) + return false; + + MachineInstr *DefMI = MRI->getVRegDef(SrcReg); + if (DefMI->isCopyLike()) + return false; + LLVM_DEBUG(dbgs() << "Coalescing: " << *DefMI); + LLVM_DEBUG(dbgs() << "*** to: " << MI); + MRI->replaceRegWith(DstReg, SrcReg); + MI.eraseFromParent(); + + // Conservatively, clear any kill flags, since it's possible that they are no + // longer correct. + MRI->clearKillFlags(SrcReg); + + ++NumCoalesces; + return true; +} + +/// AllUsesDominatedByBlock - Return true if all uses of the specified register +/// occur in blocks dominated by the specified block. If any use is in the +/// definition block, then return false since it is never legal to move def +/// after uses. +bool +MachineSinking::AllUsesDominatedByBlock(unsigned Reg, + MachineBasicBlock *MBB, + MachineBasicBlock *DefMBB, + bool &BreakPHIEdge, + bool &LocalUse) const { + assert(Register::isVirtualRegister(Reg) && "Only makes sense for vregs"); + + // Ignore debug uses because debug info doesn't affect the code. + if (MRI->use_nodbg_empty(Reg)) + return true; + + // BreakPHIEdge is true if all the uses are in the successor MBB being sunken + // into and they are all PHI nodes. In this case, machine-sink must break + // the critical edge first. e.g. + // + // %bb.1: + // Predecessors according to CFG: %bb.0 + // ... + // %def = DEC64_32r %x, implicit-def dead %eflags + // ... + // JE_4 <%bb.37>, implicit %eflags + // Successors according to CFG: %bb.37 %bb.2 + // + // %bb.2: + // %p = PHI %y, %bb.0, %def, %bb.1 + if (all_of(MRI->use_nodbg_operands(Reg), [&](MachineOperand &MO) { + MachineInstr *UseInst = MO.getParent(); + unsigned OpNo = UseInst->getOperandNo(&MO); + MachineBasicBlock *UseBlock = UseInst->getParent(); + return UseBlock == MBB && UseInst->isPHI() && + UseInst->getOperand(OpNo + 1).getMBB() == DefMBB; + })) { + BreakPHIEdge = true; + return true; + } + + for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) { + // Determine the block of the use. + MachineInstr *UseInst = MO.getParent(); + unsigned OpNo = &MO - &UseInst->getOperand(0); + MachineBasicBlock *UseBlock = UseInst->getParent(); + if (UseInst->isPHI()) { + // PHI nodes use the operand in the predecessor block, not the block with + // the PHI. + UseBlock = UseInst->getOperand(OpNo+1).getMBB(); + } else if (UseBlock == DefMBB) { + LocalUse = true; + return false; + } + + // Check that it dominates. + if (!DT->dominates(MBB, UseBlock)) + return false; + } + + return true; +} + +bool MachineSinking::runOnMachineFunction(MachineFunction &MF) { + if (skipFunction(MF.getFunction())) + return false; + + LLVM_DEBUG(dbgs() << "******** Machine Sinking ********\n"); + + TII = MF.getSubtarget().getInstrInfo(); + TRI = MF.getSubtarget().getRegisterInfo(); + MRI = &MF.getRegInfo(); + DT = &getAnalysis<MachineDominatorTree>(); + PDT = &getAnalysis<MachinePostDominatorTree>(); + LI = &getAnalysis<MachineLoopInfo>(); + MBFI = UseBlockFreqInfo ? &getAnalysis<MachineBlockFrequencyInfo>() : nullptr; + MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); + AA = &getAnalysis<AAResultsWrapperPass>().getAAResults(); + + bool EverMadeChange = false; + + while (true) { + bool MadeChange = false; + + // Process all basic blocks. + CEBCandidates.clear(); + ToSplit.clear(); + for (auto &MBB: MF) + MadeChange |= ProcessBlock(MBB); + + // If we have anything we marked as toSplit, split it now. + for (auto &Pair : ToSplit) { + auto NewSucc = Pair.first->SplitCriticalEdge(Pair.second, *this); + if (NewSucc != nullptr) { + LLVM_DEBUG(dbgs() << " *** Splitting critical edge: " + << printMBBReference(*Pair.first) << " -- " + << printMBBReference(*NewSucc) << " -- " + << printMBBReference(*Pair.second) << '\n'); + if (MBFI) { + auto NewSuccFreq = MBFI->getBlockFreq(Pair.first) * + MBPI->getEdgeProbability(Pair.first, NewSucc); + MBFI->setBlockFreq(NewSucc, NewSuccFreq.getFrequency()); + } + MadeChange = true; + ++NumSplit; + } else + LLVM_DEBUG(dbgs() << " *** Not legal to break critical edge\n"); + } + // If this iteration over the code changed anything, keep iterating. + if (!MadeChange) break; + EverMadeChange = true; + } + + // Now clear any kill flags for recorded registers. + for (auto I : RegsToClearKillFlags) + MRI->clearKillFlags(I); + RegsToClearKillFlags.clear(); + + return EverMadeChange; +} + +bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) { + // Can't sink anything out of a block that has less than two successors. + if (MBB.succ_size() <= 1 || MBB.empty()) return false; + + // Don't bother sinking code out of unreachable blocks. In addition to being + // unprofitable, it can also lead to infinite looping, because in an + // unreachable loop there may be nowhere to stop. + if (!DT->isReachableFromEntry(&MBB)) return false; + + bool MadeChange = false; + + // Cache all successors, sorted by frequency info and loop depth. + AllSuccsCache AllSuccessors; + + // Walk the basic block bottom-up. Remember if we saw a store. + MachineBasicBlock::iterator I = MBB.end(); + --I; + bool ProcessedBegin, SawStore = false; + do { + MachineInstr &MI = *I; // The instruction to sink. + + // Predecrement I (if it's not begin) so that it isn't invalidated by + // sinking. + ProcessedBegin = I == MBB.begin(); + if (!ProcessedBegin) + --I; + + if (MI.isDebugInstr()) { + if (MI.isDebugValue()) + ProcessDbgInst(MI); + continue; + } + + bool Joined = PerformTrivialForwardCoalescing(MI, &MBB); + if (Joined) { + MadeChange = true; + continue; + } + + if (SinkInstruction(MI, SawStore, AllSuccessors)) { + ++NumSunk; + MadeChange = true; + } + + // If we just processed the first instruction in the block, we're done. + } while (!ProcessedBegin); + + SeenDbgUsers.clear(); + SeenDbgVars.clear(); + + return MadeChange; +} + +void MachineSinking::ProcessDbgInst(MachineInstr &MI) { + // When we see DBG_VALUEs for registers, record any vreg it reads, so that + // we know what to sink if the vreg def sinks. + assert(MI.isDebugValue() && "Expected DBG_VALUE for processing"); + + DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(), + MI.getDebugLoc()->getInlinedAt()); + bool SeenBefore = SeenDbgVars.count(Var) != 0; + + MachineOperand &MO = MI.getDebugOperand(0); + if (MO.isReg() && MO.getReg().isVirtual()) + SeenDbgUsers[MO.getReg()].push_back(SeenDbgUser(&MI, SeenBefore)); + + // Record the variable for any DBG_VALUE, to avoid re-ordering any of them. + SeenDbgVars.insert(Var); +} + +bool MachineSinking::isWorthBreakingCriticalEdge(MachineInstr &MI, + MachineBasicBlock *From, + MachineBasicBlock *To) { + // FIXME: Need much better heuristics. + + // If the pass has already considered breaking this edge (during this pass + // through the function), then let's go ahead and break it. This means + // sinking multiple "cheap" instructions into the same block. + if (!CEBCandidates.insert(std::make_pair(From, To)).second) + return true; + + if (!MI.isCopy() && !TII->isAsCheapAsAMove(MI)) + return true; + + if (From->isSuccessor(To) && MBPI->getEdgeProbability(From, To) <= + BranchProbability(SplitEdgeProbabilityThreshold, 100)) + return true; + + // MI is cheap, we probably don't want to break the critical edge for it. + // However, if this would allow some definitions of its source operands + // to be sunk then it's probably worth it. + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + const MachineOperand &MO = MI.getOperand(i); + if (!MO.isReg() || !MO.isUse()) + continue; + Register Reg = MO.getReg(); + if (Reg == 0) + continue; + + // We don't move live definitions of physical registers, + // so sinking their uses won't enable any opportunities. + if (Register::isPhysicalRegister(Reg)) + continue; + + // If this instruction is the only user of a virtual register, + // check if breaking the edge will enable sinking + // both this instruction and the defining instruction. + if (MRI->hasOneNonDBGUse(Reg)) { + // If the definition resides in same MBB, + // claim it's likely we can sink these together. + // If definition resides elsewhere, we aren't + // blocking it from being sunk so don't break the edge. + MachineInstr *DefMI = MRI->getVRegDef(Reg); + if (DefMI->getParent() == MI.getParent()) + return true; + } + } + + return false; +} + +bool MachineSinking::PostponeSplitCriticalEdge(MachineInstr &MI, + MachineBasicBlock *FromBB, + MachineBasicBlock *ToBB, + bool BreakPHIEdge) { + if (!isWorthBreakingCriticalEdge(MI, FromBB, ToBB)) + return false; + + // Avoid breaking back edge. From == To means backedge for single BB loop. + if (!SplitEdges || FromBB == ToBB) + return false; + + // Check for backedges of more "complex" loops. + if (LI->getLoopFor(FromBB) == LI->getLoopFor(ToBB) && + LI->isLoopHeader(ToBB)) + return false; + + // It's not always legal to break critical edges and sink the computation + // to the edge. + // + // %bb.1: + // v1024 + // Beq %bb.3 + // <fallthrough> + // %bb.2: + // ... no uses of v1024 + // <fallthrough> + // %bb.3: + // ... + // = v1024 + // + // If %bb.1 -> %bb.3 edge is broken and computation of v1024 is inserted: + // + // %bb.1: + // ... + // Bne %bb.2 + // %bb.4: + // v1024 = + // B %bb.3 + // %bb.2: + // ... no uses of v1024 + // <fallthrough> + // %bb.3: + // ... + // = v1024 + // + // This is incorrect since v1024 is not computed along the %bb.1->%bb.2->%bb.3 + // flow. We need to ensure the new basic block where the computation is + // sunk to dominates all the uses. + // It's only legal to break critical edge and sink the computation to the + // new block if all the predecessors of "To", except for "From", are + // not dominated by "From". Given SSA property, this means these + // predecessors are dominated by "To". + // + // There is no need to do this check if all the uses are PHI nodes. PHI + // sources are only defined on the specific predecessor edges. + if (!BreakPHIEdge) { + for (MachineBasicBlock::pred_iterator PI = ToBB->pred_begin(), + E = ToBB->pred_end(); PI != E; ++PI) { + if (*PI == FromBB) + continue; + if (!DT->dominates(ToBB, *PI)) + return false; + } + } + + ToSplit.insert(std::make_pair(FromBB, ToBB)); + + return true; +} + +/// isProfitableToSinkTo - Return true if it is profitable to sink MI. +bool MachineSinking::isProfitableToSinkTo(unsigned Reg, MachineInstr &MI, + MachineBasicBlock *MBB, + MachineBasicBlock *SuccToSinkTo, + AllSuccsCache &AllSuccessors) { + assert (SuccToSinkTo && "Invalid SinkTo Candidate BB"); + + if (MBB == SuccToSinkTo) + return false; + + // It is profitable if SuccToSinkTo does not post dominate current block. + if (!PDT->dominates(SuccToSinkTo, MBB)) + return true; + + // It is profitable to sink an instruction from a deeper loop to a shallower + // loop, even if the latter post-dominates the former (PR21115). + if (LI->getLoopDepth(MBB) > LI->getLoopDepth(SuccToSinkTo)) + return true; + + // Check if only use in post dominated block is PHI instruction. + bool NonPHIUse = false; + for (MachineInstr &UseInst : MRI->use_nodbg_instructions(Reg)) { + MachineBasicBlock *UseBlock = UseInst.getParent(); + if (UseBlock == SuccToSinkTo && !UseInst.isPHI()) + NonPHIUse = true; + } + if (!NonPHIUse) + return true; + + // If SuccToSinkTo post dominates then also it may be profitable if MI + // can further profitably sinked into another block in next round. + bool BreakPHIEdge = false; + // FIXME - If finding successor is compile time expensive then cache results. + if (MachineBasicBlock *MBB2 = + FindSuccToSinkTo(MI, SuccToSinkTo, BreakPHIEdge, AllSuccessors)) + return isProfitableToSinkTo(Reg, MI, SuccToSinkTo, MBB2, AllSuccessors); + + // If SuccToSinkTo is final destination and it is a post dominator of current + // block then it is not profitable to sink MI into SuccToSinkTo block. + return false; +} + +/// Get the sorted sequence of successors for this MachineBasicBlock, possibly +/// computing it if it was not already cached. +SmallVector<MachineBasicBlock *, 4> & +MachineSinking::GetAllSortedSuccessors(MachineInstr &MI, MachineBasicBlock *MBB, + AllSuccsCache &AllSuccessors) const { + // Do we have the sorted successors in cache ? + auto Succs = AllSuccessors.find(MBB); + if (Succs != AllSuccessors.end()) + return Succs->second; + + SmallVector<MachineBasicBlock *, 4> AllSuccs(MBB->succ_begin(), + MBB->succ_end()); + + // Handle cases where sinking can happen but where the sink point isn't a + // successor. For example: + // + // x = computation + // if () {} else {} + // use x + // + for (MachineDomTreeNode *DTChild : DT->getNode(MBB)->children()) { + // DomTree children of MBB that have MBB as immediate dominator are added. + if (DTChild->getIDom()->getBlock() == MI.getParent() && + // Skip MBBs already added to the AllSuccs vector above. + !MBB->isSuccessor(DTChild->getBlock())) + AllSuccs.push_back(DTChild->getBlock()); + } + + // Sort Successors according to their loop depth or block frequency info. + llvm::stable_sort( + AllSuccs, [this](const MachineBasicBlock *L, const MachineBasicBlock *R) { + uint64_t LHSFreq = MBFI ? MBFI->getBlockFreq(L).getFrequency() : 0; + uint64_t RHSFreq = MBFI ? MBFI->getBlockFreq(R).getFrequency() : 0; + bool HasBlockFreq = LHSFreq != 0 && RHSFreq != 0; + return HasBlockFreq ? LHSFreq < RHSFreq + : LI->getLoopDepth(L) < LI->getLoopDepth(R); + }); + + auto it = AllSuccessors.insert(std::make_pair(MBB, AllSuccs)); + + return it.first->second; +} + +/// FindSuccToSinkTo - Find a successor to sink this instruction to. +MachineBasicBlock * +MachineSinking::FindSuccToSinkTo(MachineInstr &MI, MachineBasicBlock *MBB, + bool &BreakPHIEdge, + AllSuccsCache &AllSuccessors) { + assert (MBB && "Invalid MachineBasicBlock!"); + + // Loop over all the operands of the specified instruction. If there is + // anything we can't handle, bail out. + + // SuccToSinkTo - This is the successor to sink this instruction to, once we + // decide. + MachineBasicBlock *SuccToSinkTo = nullptr; + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + const MachineOperand &MO = MI.getOperand(i); + if (!MO.isReg()) continue; // Ignore non-register operands. + + Register Reg = MO.getReg(); + if (Reg == 0) continue; + + if (Register::isPhysicalRegister(Reg)) { + if (MO.isUse()) { + // If the physreg has no defs anywhere, it's just an ambient register + // and we can freely move its uses. Alternatively, if it's allocatable, + // it could get allocated to something with a def during allocation. + if (!MRI->isConstantPhysReg(Reg)) + return nullptr; + } else if (!MO.isDead()) { + // A def that isn't dead. We can't move it. + return nullptr; + } + } else { + // Virtual register uses are always safe to sink. + if (MO.isUse()) continue; + + // If it's not safe to move defs of the register class, then abort. + if (!TII->isSafeToMoveRegClassDefs(MRI->getRegClass(Reg))) + return nullptr; + + // Virtual register defs can only be sunk if all their uses are in blocks + // dominated by one of the successors. + if (SuccToSinkTo) { + // If a previous operand picked a block to sink to, then this operand + // must be sinkable to the same block. + bool LocalUse = false; + if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo, MBB, + BreakPHIEdge, LocalUse)) + return nullptr; + + continue; + } + + // Otherwise, we should look at all the successors and decide which one + // we should sink to. If we have reliable block frequency information + // (frequency != 0) available, give successors with smaller frequencies + // higher priority, otherwise prioritize smaller loop depths. + for (MachineBasicBlock *SuccBlock : + GetAllSortedSuccessors(MI, MBB, AllSuccessors)) { + bool LocalUse = false; + if (AllUsesDominatedByBlock(Reg, SuccBlock, MBB, + BreakPHIEdge, LocalUse)) { + SuccToSinkTo = SuccBlock; + break; + } + if (LocalUse) + // Def is used locally, it's never safe to move this def. + return nullptr; + } + + // If we couldn't find a block to sink to, ignore this instruction. + if (!SuccToSinkTo) + return nullptr; + if (!isProfitableToSinkTo(Reg, MI, MBB, SuccToSinkTo, AllSuccessors)) + return nullptr; + } + } + + // It is not possible to sink an instruction into its own block. This can + // happen with loops. + if (MBB == SuccToSinkTo) + return nullptr; + + // It's not safe to sink instructions to EH landing pad. Control flow into + // landing pad is implicitly defined. + if (SuccToSinkTo && SuccToSinkTo->isEHPad()) + return nullptr; + + // It ought to be okay to sink instructions into an INLINEASM_BR target, but + // only if we make sure that MI occurs _before_ an INLINEASM_BR instruction in + // the source block (which this code does not yet do). So for now, forbid + // doing so. + if (SuccToSinkTo && SuccToSinkTo->isInlineAsmBrIndirectTarget()) + return nullptr; + + return SuccToSinkTo; +} + +/// Return true if MI is likely to be usable as a memory operation by the +/// implicit null check optimization. +/// +/// This is a "best effort" heuristic, and should not be relied upon for +/// correctness. This returning true does not guarantee that the implicit null +/// check optimization is legal over MI, and this returning false does not +/// guarantee MI cannot possibly be used to do a null check. +static bool SinkingPreventsImplicitNullCheck(MachineInstr &MI, + const TargetInstrInfo *TII, + const TargetRegisterInfo *TRI) { + using MachineBranchPredicate = TargetInstrInfo::MachineBranchPredicate; + + auto *MBB = MI.getParent(); + if (MBB->pred_size() != 1) + return false; + + auto *PredMBB = *MBB->pred_begin(); + auto *PredBB = PredMBB->getBasicBlock(); + + // Frontends that don't use implicit null checks have no reason to emit + // branches with make.implicit metadata, and this function should always + // return false for them. + if (!PredBB || + !PredBB->getTerminator()->getMetadata(LLVMContext::MD_make_implicit)) + return false; + + const MachineOperand *BaseOp; + int64_t Offset; + bool OffsetIsScalable; + if (!TII->getMemOperandWithOffset(MI, BaseOp, Offset, OffsetIsScalable, TRI)) + return false; + + if (!BaseOp->isReg()) + return false; + + if (!(MI.mayLoad() && !MI.isPredicable())) + return false; + + MachineBranchPredicate MBP; + if (TII->analyzeBranchPredicate(*PredMBB, MBP, false)) + return false; + + return MBP.LHS.isReg() && MBP.RHS.isImm() && MBP.RHS.getImm() == 0 && + (MBP.Predicate == MachineBranchPredicate::PRED_NE || + MBP.Predicate == MachineBranchPredicate::PRED_EQ) && + MBP.LHS.getReg() == BaseOp->getReg(); +} + +/// If the sunk instruction is a copy, try to forward the copy instead of +/// leaving an 'undef' DBG_VALUE in the original location. Don't do this if +/// there's any subregister weirdness involved. Returns true if copy +/// propagation occurred. +static bool attemptDebugCopyProp(MachineInstr &SinkInst, MachineInstr &DbgMI) { + const MachineRegisterInfo &MRI = SinkInst.getMF()->getRegInfo(); + const TargetInstrInfo &TII = *SinkInst.getMF()->getSubtarget().getInstrInfo(); + + // Copy DBG_VALUE operand and set the original to undef. We then check to + // see whether this is something that can be copy-forwarded. If it isn't, + // continue around the loop. + MachineOperand &DbgMO = DbgMI.getDebugOperand(0); + + const MachineOperand *SrcMO = nullptr, *DstMO = nullptr; + auto CopyOperands = TII.isCopyInstr(SinkInst); + if (!CopyOperands) + return false; + SrcMO = CopyOperands->Source; + DstMO = CopyOperands->Destination; + + // Check validity of forwarding this copy. + bool PostRA = MRI.getNumVirtRegs() == 0; + + // Trying to forward between physical and virtual registers is too hard. + if (DbgMO.getReg().isVirtual() != SrcMO->getReg().isVirtual()) + return false; + + // Only try virtual register copy-forwarding before regalloc, and physical + // register copy-forwarding after regalloc. + bool arePhysRegs = !DbgMO.getReg().isVirtual(); + if (arePhysRegs != PostRA) + return false; + + // Pre-regalloc, only forward if all subregisters agree (or there are no + // subregs at all). More analysis might recover some forwardable copies. + if (!PostRA && (DbgMO.getSubReg() != SrcMO->getSubReg() || + DbgMO.getSubReg() != DstMO->getSubReg())) + return false; + + // Post-regalloc, we may be sinking a DBG_VALUE of a sub or super-register + // of this copy. Only forward the copy if the DBG_VALUE operand exactly + // matches the copy destination. + if (PostRA && DbgMO.getReg() != DstMO->getReg()) + return false; + + DbgMO.setReg(SrcMO->getReg()); + DbgMO.setSubReg(SrcMO->getSubReg()); + return true; +} + +/// Sink an instruction and its associated debug instructions. +static void performSink(MachineInstr &MI, MachineBasicBlock &SuccToSinkTo, + MachineBasicBlock::iterator InsertPos, + SmallVectorImpl<MachineInstr *> &DbgValuesToSink) { + + // If we cannot find a location to use (merge with), then we erase the debug + // location to prevent debug-info driven tools from potentially reporting + // wrong location information. + if (!SuccToSinkTo.empty() && InsertPos != SuccToSinkTo.end()) + MI.setDebugLoc(DILocation::getMergedLocation(MI.getDebugLoc(), + InsertPos->getDebugLoc())); + else + MI.setDebugLoc(DebugLoc()); + + // Move the instruction. + MachineBasicBlock *ParentBlock = MI.getParent(); + SuccToSinkTo.splice(InsertPos, ParentBlock, MI, + ++MachineBasicBlock::iterator(MI)); + + // Sink a copy of debug users to the insert position. Mark the original + // DBG_VALUE location as 'undef', indicating that any earlier variable + // location should be terminated as we've optimised away the value at this + // point. + for (SmallVectorImpl<MachineInstr *>::iterator DBI = DbgValuesToSink.begin(), + DBE = DbgValuesToSink.end(); + DBI != DBE; ++DBI) { + MachineInstr *DbgMI = *DBI; + MachineInstr *NewDbgMI = DbgMI->getMF()->CloneMachineInstr(*DBI); + SuccToSinkTo.insert(InsertPos, NewDbgMI); + + if (!attemptDebugCopyProp(MI, *DbgMI)) + DbgMI->setDebugValueUndef(); + } +} + +/// SinkInstruction - Determine whether it is safe to sink the specified machine +/// instruction out of its current block into a successor. +bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore, + AllSuccsCache &AllSuccessors) { + // Don't sink instructions that the target prefers not to sink. + if (!TII->shouldSink(MI)) + return false; + + // Check if it's safe to move the instruction. + if (!MI.isSafeToMove(AA, SawStore)) + return false; + + // Convergent operations may not be made control-dependent on additional + // values. + if (MI.isConvergent()) + return false; + + // Don't break implicit null checks. This is a performance heuristic, and not + // required for correctness. + if (SinkingPreventsImplicitNullCheck(MI, TII, TRI)) + return false; + + // FIXME: This should include support for sinking instructions within the + // block they are currently in to shorten the live ranges. We often get + // instructions sunk into the top of a large block, but it would be better to + // also sink them down before their first use in the block. This xform has to + // be careful not to *increase* register pressure though, e.g. sinking + // "x = y + z" down if it kills y and z would increase the live ranges of y + // and z and only shrink the live range of x. + + bool BreakPHIEdge = false; + MachineBasicBlock *ParentBlock = MI.getParent(); + MachineBasicBlock *SuccToSinkTo = + FindSuccToSinkTo(MI, ParentBlock, BreakPHIEdge, AllSuccessors); + + // If there are no outputs, it must have side-effects. + if (!SuccToSinkTo) + return false; + + // If the instruction to move defines a dead physical register which is live + // when leaving the basic block, don't move it because it could turn into a + // "zombie" define of that preg. E.g., EFLAGS. (<rdar://problem/8030636>) + for (unsigned I = 0, E = MI.getNumOperands(); I != E; ++I) { + const MachineOperand &MO = MI.getOperand(I); + if (!MO.isReg()) continue; + Register Reg = MO.getReg(); + if (Reg == 0 || !Register::isPhysicalRegister(Reg)) + continue; + if (SuccToSinkTo->isLiveIn(Reg)) + return false; + } + + LLVM_DEBUG(dbgs() << "Sink instr " << MI << "\tinto block " << *SuccToSinkTo); + + // If the block has multiple predecessors, this is a critical edge. + // Decide if we can sink along it or need to break the edge. + if (SuccToSinkTo->pred_size() > 1) { + // We cannot sink a load across a critical edge - there may be stores in + // other code paths. + bool TryBreak = false; + bool store = true; + if (!MI.isSafeToMove(AA, store)) { + LLVM_DEBUG(dbgs() << " *** NOTE: Won't sink load along critical edge.\n"); + TryBreak = true; + } + + // We don't want to sink across a critical edge if we don't dominate the + // successor. We could be introducing calculations to new code paths. + if (!TryBreak && !DT->dominates(ParentBlock, SuccToSinkTo)) { + LLVM_DEBUG(dbgs() << " *** NOTE: Critical edge found\n"); + TryBreak = true; + } + + // Don't sink instructions into a loop. + if (!TryBreak && LI->isLoopHeader(SuccToSinkTo)) { + LLVM_DEBUG(dbgs() << " *** NOTE: Loop header found\n"); + TryBreak = true; + } + + // Otherwise we are OK with sinking along a critical edge. + if (!TryBreak) + LLVM_DEBUG(dbgs() << "Sinking along critical edge.\n"); + else { + // Mark this edge as to be split. + // If the edge can actually be split, the next iteration of the main loop + // will sink MI in the newly created block. + bool Status = + PostponeSplitCriticalEdge(MI, ParentBlock, SuccToSinkTo, BreakPHIEdge); + if (!Status) + LLVM_DEBUG(dbgs() << " *** PUNTING: Not legal or profitable to " + "break critical edge\n"); + // The instruction will not be sunk this time. + return false; + } + } + + if (BreakPHIEdge) { + // BreakPHIEdge is true if all the uses are in the successor MBB being + // sunken into and they are all PHI nodes. In this case, machine-sink must + // break the critical edge first. + bool Status = PostponeSplitCriticalEdge(MI, ParentBlock, + SuccToSinkTo, BreakPHIEdge); + if (!Status) + LLVM_DEBUG(dbgs() << " *** PUNTING: Not legal or profitable to " + "break critical edge\n"); + // The instruction will not be sunk this time. + return false; + } + + // Determine where to insert into. Skip phi nodes. + MachineBasicBlock::iterator InsertPos = SuccToSinkTo->begin(); + while (InsertPos != SuccToSinkTo->end() && InsertPos->isPHI()) + ++InsertPos; + + // Collect debug users of any vreg that this inst defines. + SmallVector<MachineInstr *, 4> DbgUsersToSink; + for (auto &MO : MI.operands()) { + if (!MO.isReg() || !MO.isDef() || !MO.getReg().isVirtual()) + continue; + if (!SeenDbgUsers.count(MO.getReg())) + continue; + + // Sink any users that don't pass any other DBG_VALUEs for this variable. + auto &Users = SeenDbgUsers[MO.getReg()]; + for (auto &User : Users) { + MachineInstr *DbgMI = User.getPointer(); + if (User.getInt()) { + // This DBG_VALUE would re-order assignments. If we can't copy-propagate + // it, it can't be recovered. Set it undef. + if (!attemptDebugCopyProp(MI, *DbgMI)) + DbgMI->setDebugValueUndef(); + } else { + DbgUsersToSink.push_back(DbgMI); + } + } + } + + // After sinking, some debug users may not be dominated any more. If possible, + // copy-propagate their operands. As it's expensive, don't do this if there's + // no debuginfo in the program. + if (MI.getMF()->getFunction().getSubprogram() && MI.isCopy()) + SalvageUnsunkDebugUsersOfCopy(MI, SuccToSinkTo); + + performSink(MI, *SuccToSinkTo, InsertPos, DbgUsersToSink); + + // Conservatively, clear any kill flags, since it's possible that they are no + // longer correct. + // Note that we have to clear the kill flags for any register this instruction + // uses as we may sink over another instruction which currently kills the + // used registers. + for (MachineOperand &MO : MI.operands()) { + if (MO.isReg() && MO.isUse()) + RegsToClearKillFlags.set(MO.getReg()); // Remember to clear kill flags. + } + + return true; +} + +void MachineSinking::SalvageUnsunkDebugUsersOfCopy( + MachineInstr &MI, MachineBasicBlock *TargetBlock) { + assert(MI.isCopy()); + assert(MI.getOperand(1).isReg()); + + // Enumerate all users of vreg operands that are def'd. Skip those that will + // be sunk. For the rest, if they are not dominated by the block we will sink + // MI into, propagate the copy source to them. + SmallVector<MachineInstr *, 4> DbgDefUsers; + const MachineRegisterInfo &MRI = MI.getMF()->getRegInfo(); + for (auto &MO : MI.operands()) { + if (!MO.isReg() || !MO.isDef() || !MO.getReg().isVirtual()) + continue; + for (auto &User : MRI.use_instructions(MO.getReg())) { + if (!User.isDebugValue() || DT->dominates(TargetBlock, User.getParent())) + continue; + + // If is in same block, will either sink or be use-before-def. + if (User.getParent() == MI.getParent()) + continue; + + assert(User.getDebugOperand(0).isReg() && + "DBG_VALUE user of vreg, but non reg operand?"); + DbgDefUsers.push_back(&User); + } + } + + // Point the users of this copy that are no longer dominated, at the source + // of the copy. + for (auto *User : DbgDefUsers) { + User->getDebugOperand(0).setReg(MI.getOperand(1).getReg()); + User->getDebugOperand(0).setSubReg(MI.getOperand(1).getSubReg()); + } +} + +//===----------------------------------------------------------------------===// +// This pass is not intended to be a replacement or a complete alternative +// for the pre-ra machine sink pass. It is only designed to sink COPY +// instructions which should be handled after RA. +// +// This pass sinks COPY instructions into a successor block, if the COPY is not +// used in the current block and the COPY is live-in to a single successor +// (i.e., doesn't require the COPY to be duplicated). This avoids executing the +// copy on paths where their results aren't needed. This also exposes +// additional opportunites for dead copy elimination and shrink wrapping. +// +// These copies were either not handled by or are inserted after the MachineSink +// pass. As an example of the former case, the MachineSink pass cannot sink +// COPY instructions with allocatable source registers; for AArch64 these type +// of copy instructions are frequently used to move function parameters (PhyReg) +// into virtual registers in the entry block. +// +// For the machine IR below, this pass will sink %w19 in the entry into its +// successor (%bb.1) because %w19 is only live-in in %bb.1. +// %bb.0: +// %wzr = SUBSWri %w1, 1 +// %w19 = COPY %w0 +// Bcc 11, %bb.2 +// %bb.1: +// Live Ins: %w19 +// BL @fun +// %w0 = ADDWrr %w0, %w19 +// RET %w0 +// %bb.2: +// %w0 = COPY %wzr +// RET %w0 +// As we sink %w19 (CSR in AArch64) into %bb.1, the shrink-wrapping pass will be +// able to see %bb.0 as a candidate. +//===----------------------------------------------------------------------===// +namespace { + +class PostRAMachineSinking : public MachineFunctionPass { +public: + bool runOnMachineFunction(MachineFunction &MF) override; + + static char ID; + PostRAMachineSinking() : MachineFunctionPass(ID) {} + StringRef getPassName() const override { return "PostRA Machine Sink"; } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + MachineFunctionPass::getAnalysisUsage(AU); + } + + MachineFunctionProperties getRequiredProperties() const override { + return MachineFunctionProperties().set( + MachineFunctionProperties::Property::NoVRegs); + } + +private: + /// Track which register units have been modified and used. + LiveRegUnits ModifiedRegUnits, UsedRegUnits; + + /// Track DBG_VALUEs of (unmodified) register units. Each DBG_VALUE has an + /// entry in this map for each unit it touches. + DenseMap<unsigned, TinyPtrVector<MachineInstr *>> SeenDbgInstrs; + + /// Sink Copy instructions unused in the same block close to their uses in + /// successors. + bool tryToSinkCopy(MachineBasicBlock &BB, MachineFunction &MF, + const TargetRegisterInfo *TRI, const TargetInstrInfo *TII); +}; +} // namespace + +char PostRAMachineSinking::ID = 0; +char &llvm::PostRAMachineSinkingID = PostRAMachineSinking::ID; + +INITIALIZE_PASS(PostRAMachineSinking, "postra-machine-sink", + "PostRA Machine Sink", false, false) + +static bool aliasWithRegsInLiveIn(MachineBasicBlock &MBB, unsigned Reg, + const TargetRegisterInfo *TRI) { + LiveRegUnits LiveInRegUnits(*TRI); + LiveInRegUnits.addLiveIns(MBB); + return !LiveInRegUnits.available(Reg); +} + +static MachineBasicBlock * +getSingleLiveInSuccBB(MachineBasicBlock &CurBB, + const SmallPtrSetImpl<MachineBasicBlock *> &SinkableBBs, + unsigned Reg, const TargetRegisterInfo *TRI) { + // Try to find a single sinkable successor in which Reg is live-in. + MachineBasicBlock *BB = nullptr; + for (auto *SI : SinkableBBs) { + if (aliasWithRegsInLiveIn(*SI, Reg, TRI)) { + // If BB is set here, Reg is live-in to at least two sinkable successors, + // so quit. + if (BB) + return nullptr; + BB = SI; + } + } + // Reg is not live-in to any sinkable successors. + if (!BB) + return nullptr; + + // Check if any register aliased with Reg is live-in in other successors. + for (auto *SI : CurBB.successors()) { + if (!SinkableBBs.count(SI) && aliasWithRegsInLiveIn(*SI, Reg, TRI)) + return nullptr; + } + return BB; +} + +static MachineBasicBlock * +getSingleLiveInSuccBB(MachineBasicBlock &CurBB, + const SmallPtrSetImpl<MachineBasicBlock *> &SinkableBBs, + ArrayRef<unsigned> DefedRegsInCopy, + const TargetRegisterInfo *TRI) { + MachineBasicBlock *SingleBB = nullptr; + for (auto DefReg : DefedRegsInCopy) { + MachineBasicBlock *BB = + getSingleLiveInSuccBB(CurBB, SinkableBBs, DefReg, TRI); + if (!BB || (SingleBB && SingleBB != BB)) + return nullptr; + SingleBB = BB; + } + return SingleBB; +} + +static void clearKillFlags(MachineInstr *MI, MachineBasicBlock &CurBB, + SmallVectorImpl<unsigned> &UsedOpsInCopy, + LiveRegUnits &UsedRegUnits, + const TargetRegisterInfo *TRI) { + for (auto U : UsedOpsInCopy) { + MachineOperand &MO = MI->getOperand(U); + Register SrcReg = MO.getReg(); + if (!UsedRegUnits.available(SrcReg)) { + MachineBasicBlock::iterator NI = std::next(MI->getIterator()); + for (MachineInstr &UI : make_range(NI, CurBB.end())) { + if (UI.killsRegister(SrcReg, TRI)) { + UI.clearRegisterKills(SrcReg, TRI); + MO.setIsKill(true); + break; + } + } + } + } +} + +static void updateLiveIn(MachineInstr *MI, MachineBasicBlock *SuccBB, + SmallVectorImpl<unsigned> &UsedOpsInCopy, + SmallVectorImpl<unsigned> &DefedRegsInCopy) { + MachineFunction &MF = *SuccBB->getParent(); + const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo(); + for (unsigned DefReg : DefedRegsInCopy) + for (MCSubRegIterator S(DefReg, TRI, true); S.isValid(); ++S) + SuccBB->removeLiveIn(*S); + for (auto U : UsedOpsInCopy) { + Register SrcReg = MI->getOperand(U).getReg(); + LaneBitmask Mask; + for (MCRegUnitMaskIterator S(SrcReg, TRI); S.isValid(); ++S) { + Mask |= (*S).second; + } + SuccBB->addLiveIn(SrcReg, Mask.any() ? Mask : LaneBitmask::getAll()); + } + SuccBB->sortUniqueLiveIns(); +} + +static bool hasRegisterDependency(MachineInstr *MI, + SmallVectorImpl<unsigned> &UsedOpsInCopy, + SmallVectorImpl<unsigned> &DefedRegsInCopy, + LiveRegUnits &ModifiedRegUnits, + LiveRegUnits &UsedRegUnits) { + bool HasRegDependency = false; + for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI->getOperand(i); + if (!MO.isReg()) + continue; + Register Reg = MO.getReg(); + if (!Reg) + continue; + if (MO.isDef()) { + if (!ModifiedRegUnits.available(Reg) || !UsedRegUnits.available(Reg)) { + HasRegDependency = true; + break; + } + DefedRegsInCopy.push_back(Reg); + + // FIXME: instead of isUse(), readsReg() would be a better fix here, + // For example, we can ignore modifications in reg with undef. However, + // it's not perfectly clear if skipping the internal read is safe in all + // other targets. + } else if (MO.isUse()) { + if (!ModifiedRegUnits.available(Reg)) { + HasRegDependency = true; + break; + } + UsedOpsInCopy.push_back(i); + } + } + return HasRegDependency; +} + +static SmallSet<unsigned, 4> getRegUnits(unsigned Reg, + const TargetRegisterInfo *TRI) { + SmallSet<unsigned, 4> RegUnits; + for (auto RI = MCRegUnitIterator(Reg, TRI); RI.isValid(); ++RI) + RegUnits.insert(*RI); + return RegUnits; +} + +bool PostRAMachineSinking::tryToSinkCopy(MachineBasicBlock &CurBB, + MachineFunction &MF, + const TargetRegisterInfo *TRI, + const TargetInstrInfo *TII) { + SmallPtrSet<MachineBasicBlock *, 2> SinkableBBs; + // FIXME: For now, we sink only to a successor which has a single predecessor + // so that we can directly sink COPY instructions to the successor without + // adding any new block or branch instruction. + for (MachineBasicBlock *SI : CurBB.successors()) + if (!SI->livein_empty() && SI->pred_size() == 1) + SinkableBBs.insert(SI); + + if (SinkableBBs.empty()) + return false; + + bool Changed = false; + + // Track which registers have been modified and used between the end of the + // block and the current instruction. + ModifiedRegUnits.clear(); + UsedRegUnits.clear(); + SeenDbgInstrs.clear(); + + for (auto I = CurBB.rbegin(), E = CurBB.rend(); I != E;) { + MachineInstr *MI = &*I; + ++I; + + // Track the operand index for use in Copy. + SmallVector<unsigned, 2> UsedOpsInCopy; + // Track the register number defed in Copy. + SmallVector<unsigned, 2> DefedRegsInCopy; + + // We must sink this DBG_VALUE if its operand is sunk. To avoid searching + // for DBG_VALUEs later, record them when they're encountered. + if (MI->isDebugValue()) { + auto &MO = MI->getDebugOperand(0); + if (MO.isReg() && Register::isPhysicalRegister(MO.getReg())) { + // Bail if we can already tell the sink would be rejected, rather + // than needlessly accumulating lots of DBG_VALUEs. + if (hasRegisterDependency(MI, UsedOpsInCopy, DefedRegsInCopy, + ModifiedRegUnits, UsedRegUnits)) + continue; + + // Record debug use of each reg unit. + SmallSet<unsigned, 4> Units = getRegUnits(MO.getReg(), TRI); + for (unsigned Reg : Units) + SeenDbgInstrs[Reg].push_back(MI); + } + continue; + } + + if (MI->isDebugInstr()) + continue; + + // Do not move any instruction across function call. + if (MI->isCall()) + return false; + + if (!MI->isCopy() || !MI->getOperand(0).isRenamable()) { + LiveRegUnits::accumulateUsedDefed(*MI, ModifiedRegUnits, UsedRegUnits, + TRI); + continue; + } + + // Don't sink the COPY if it would violate a register dependency. + if (hasRegisterDependency(MI, UsedOpsInCopy, DefedRegsInCopy, + ModifiedRegUnits, UsedRegUnits)) { + LiveRegUnits::accumulateUsedDefed(*MI, ModifiedRegUnits, UsedRegUnits, + TRI); + continue; + } + assert((!UsedOpsInCopy.empty() && !DefedRegsInCopy.empty()) && + "Unexpect SrcReg or DefReg"); + MachineBasicBlock *SuccBB = + getSingleLiveInSuccBB(CurBB, SinkableBBs, DefedRegsInCopy, TRI); + // Don't sink if we cannot find a single sinkable successor in which Reg + // is live-in. + if (!SuccBB) { + LiveRegUnits::accumulateUsedDefed(*MI, ModifiedRegUnits, UsedRegUnits, + TRI); + continue; + } + assert((SuccBB->pred_size() == 1 && *SuccBB->pred_begin() == &CurBB) && + "Unexpected predecessor"); + + // Collect DBG_VALUEs that must sink with this copy. We've previously + // recorded which reg units that DBG_VALUEs read, if this instruction + // writes any of those units then the corresponding DBG_VALUEs must sink. + SetVector<MachineInstr *> DbgValsToSinkSet; + SmallVector<MachineInstr *, 4> DbgValsToSink; + for (auto &MO : MI->operands()) { + if (!MO.isReg() || !MO.isDef()) + continue; + + SmallSet<unsigned, 4> Units = getRegUnits(MO.getReg(), TRI); + for (unsigned Reg : Units) + for (auto *MI : SeenDbgInstrs.lookup(Reg)) + DbgValsToSinkSet.insert(MI); + } + DbgValsToSink.insert(DbgValsToSink.begin(), DbgValsToSinkSet.begin(), + DbgValsToSinkSet.end()); + + // Clear the kill flag if SrcReg is killed between MI and the end of the + // block. + clearKillFlags(MI, CurBB, UsedOpsInCopy, UsedRegUnits, TRI); + MachineBasicBlock::iterator InsertPos = SuccBB->getFirstNonPHI(); + performSink(*MI, *SuccBB, InsertPos, DbgValsToSink); + updateLiveIn(MI, SuccBB, UsedOpsInCopy, DefedRegsInCopy); + + Changed = true; + ++NumPostRACopySink; + } + return Changed; +} + +bool PostRAMachineSinking::runOnMachineFunction(MachineFunction &MF) { + if (skipFunction(MF.getFunction())) + return false; + + bool Changed = false; + const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo(); + const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo(); + + ModifiedRegUnits.init(*TRI); + UsedRegUnits.init(*TRI); + for (auto &BB : MF) + Changed |= tryToSinkCopy(BB, MF, TRI, TII); + + return Changed; +} |