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Diffstat (limited to 'llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp')
| -rw-r--r-- | llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp | 1389 |
1 files changed, 1389 insertions, 0 deletions
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp new file mode 100644 index 000000000000..7e867edaaa27 --- /dev/null +++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp @@ -0,0 +1,1389 @@ +//===-- WebAssemblyCFGStackify.cpp - CFG Stackification -------------------===// +// +// 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 +// +//===----------------------------------------------------------------------===// +/// +/// \file +/// This file implements a CFG stacking pass. +/// +/// This pass inserts BLOCK, LOOP, and TRY markers to mark the start of scopes, +/// since scope boundaries serve as the labels for WebAssembly's control +/// transfers. +/// +/// This is sufficient to convert arbitrary CFGs into a form that works on +/// WebAssembly, provided that all loops are single-entry. +/// +/// In case we use exceptions, this pass also fixes mismatches in unwind +/// destinations created during transforming CFG into wasm structured format. +/// +//===----------------------------------------------------------------------===// + +#include "WebAssembly.h" +#include "WebAssemblyExceptionInfo.h" +#include "WebAssemblyMachineFunctionInfo.h" +#include "WebAssemblySubtarget.h" +#include "WebAssemblyUtilities.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/CodeGen/MachineDominators.h" +#include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineLoopInfo.h" +#include "llvm/MC/MCAsmInfo.h" +using namespace llvm; + +#define DEBUG_TYPE "wasm-cfg-stackify" + +STATISTIC(NumUnwindMismatches, "Number of EH pad unwind mismatches found"); + +namespace { +class WebAssemblyCFGStackify final : public MachineFunctionPass { + StringRef getPassName() const override { return "WebAssembly CFG Stackify"; } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<MachineDominatorTree>(); + AU.addRequired<MachineLoopInfo>(); + AU.addRequired<WebAssemblyExceptionInfo>(); + MachineFunctionPass::getAnalysisUsage(AU); + } + + bool runOnMachineFunction(MachineFunction &MF) override; + + // For each block whose label represents the end of a scope, record the block + // which holds the beginning of the scope. This will allow us to quickly skip + // over scoped regions when walking blocks. + SmallVector<MachineBasicBlock *, 8> ScopeTops; + + // Placing markers. + void placeMarkers(MachineFunction &MF); + void placeBlockMarker(MachineBasicBlock &MBB); + void placeLoopMarker(MachineBasicBlock &MBB); + void placeTryMarker(MachineBasicBlock &MBB); + void removeUnnecessaryInstrs(MachineFunction &MF); + bool fixUnwindMismatches(MachineFunction &MF); + void rewriteDepthImmediates(MachineFunction &MF); + void fixEndsAtEndOfFunction(MachineFunction &MF); + + // For each BLOCK|LOOP|TRY, the corresponding END_(BLOCK|LOOP|TRY). + DenseMap<const MachineInstr *, MachineInstr *> BeginToEnd; + // For each END_(BLOCK|LOOP|TRY), the corresponding BLOCK|LOOP|TRY. + DenseMap<const MachineInstr *, MachineInstr *> EndToBegin; + // <TRY marker, EH pad> map + DenseMap<const MachineInstr *, MachineBasicBlock *> TryToEHPad; + // <EH pad, TRY marker> map + DenseMap<const MachineBasicBlock *, MachineInstr *> EHPadToTry; + + // There can be an appendix block at the end of each function, shared for: + // - creating a correct signature for fallthrough returns + // - target for rethrows that need to unwind to the caller, but are trapped + // inside another try/catch + MachineBasicBlock *AppendixBB = nullptr; + MachineBasicBlock *getAppendixBlock(MachineFunction &MF) { + if (!AppendixBB) { + AppendixBB = MF.CreateMachineBasicBlock(); + // Give it a fake predecessor so that AsmPrinter prints its label. + AppendixBB->addSuccessor(AppendixBB); + MF.push_back(AppendixBB); + } + return AppendixBB; + } + + // Helper functions to register / unregister scope information created by + // marker instructions. + void registerScope(MachineInstr *Begin, MachineInstr *End); + void registerTryScope(MachineInstr *Begin, MachineInstr *End, + MachineBasicBlock *EHPad); + void unregisterScope(MachineInstr *Begin); + +public: + static char ID; // Pass identification, replacement for typeid + WebAssemblyCFGStackify() : MachineFunctionPass(ID) {} + ~WebAssemblyCFGStackify() override { releaseMemory(); } + void releaseMemory() override; +}; +} // end anonymous namespace + +char WebAssemblyCFGStackify::ID = 0; +INITIALIZE_PASS(WebAssemblyCFGStackify, DEBUG_TYPE, + "Insert BLOCK/LOOP/TRY markers for WebAssembly scopes", false, + false) + +FunctionPass *llvm::createWebAssemblyCFGStackify() { + return new WebAssemblyCFGStackify(); +} + +/// Test whether Pred has any terminators explicitly branching to MBB, as +/// opposed to falling through. Note that it's possible (eg. in unoptimized +/// code) for a branch instruction to both branch to a block and fallthrough +/// to it, so we check the actual branch operands to see if there are any +/// explicit mentions. +static bool explicitlyBranchesTo(MachineBasicBlock *Pred, + MachineBasicBlock *MBB) { + for (MachineInstr &MI : Pred->terminators()) + for (MachineOperand &MO : MI.explicit_operands()) + if (MO.isMBB() && MO.getMBB() == MBB) + return true; + return false; +} + +// Returns an iterator to the earliest position possible within the MBB, +// satisfying the restrictions given by BeforeSet and AfterSet. BeforeSet +// contains instructions that should go before the marker, and AfterSet contains +// ones that should go after the marker. In this function, AfterSet is only +// used for sanity checking. +static MachineBasicBlock::iterator +getEarliestInsertPos(MachineBasicBlock *MBB, + const SmallPtrSet<const MachineInstr *, 4> &BeforeSet, + const SmallPtrSet<const MachineInstr *, 4> &AfterSet) { + auto InsertPos = MBB->end(); + while (InsertPos != MBB->begin()) { + if (BeforeSet.count(&*std::prev(InsertPos))) { +#ifndef NDEBUG + // Sanity check + for (auto Pos = InsertPos, E = MBB->begin(); Pos != E; --Pos) + assert(!AfterSet.count(&*std::prev(Pos))); +#endif + break; + } + --InsertPos; + } + return InsertPos; +} + +// Returns an iterator to the latest position possible within the MBB, +// satisfying the restrictions given by BeforeSet and AfterSet. BeforeSet +// contains instructions that should go before the marker, and AfterSet contains +// ones that should go after the marker. In this function, BeforeSet is only +// used for sanity checking. +static MachineBasicBlock::iterator +getLatestInsertPos(MachineBasicBlock *MBB, + const SmallPtrSet<const MachineInstr *, 4> &BeforeSet, + const SmallPtrSet<const MachineInstr *, 4> &AfterSet) { + auto InsertPos = MBB->begin(); + while (InsertPos != MBB->end()) { + if (AfterSet.count(&*InsertPos)) { +#ifndef NDEBUG + // Sanity check + for (auto Pos = InsertPos, E = MBB->end(); Pos != E; ++Pos) + assert(!BeforeSet.count(&*Pos)); +#endif + break; + } + ++InsertPos; + } + return InsertPos; +} + +void WebAssemblyCFGStackify::registerScope(MachineInstr *Begin, + MachineInstr *End) { + BeginToEnd[Begin] = End; + EndToBegin[End] = Begin; +} + +void WebAssemblyCFGStackify::registerTryScope(MachineInstr *Begin, + MachineInstr *End, + MachineBasicBlock *EHPad) { + registerScope(Begin, End); + TryToEHPad[Begin] = EHPad; + EHPadToTry[EHPad] = Begin; +} + +void WebAssemblyCFGStackify::unregisterScope(MachineInstr *Begin) { + assert(BeginToEnd.count(Begin)); + MachineInstr *End = BeginToEnd[Begin]; + assert(EndToBegin.count(End)); + BeginToEnd.erase(Begin); + EndToBegin.erase(End); + MachineBasicBlock *EHPad = TryToEHPad.lookup(Begin); + if (EHPad) { + assert(EHPadToTry.count(EHPad)); + TryToEHPad.erase(Begin); + EHPadToTry.erase(EHPad); + } +} + +/// Insert a BLOCK marker for branches to MBB (if needed). +// TODO Consider a more generalized way of handling block (and also loop and +// try) signatures when we implement the multi-value proposal later. +void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) { + assert(!MBB.isEHPad()); + MachineFunction &MF = *MBB.getParent(); + auto &MDT = getAnalysis<MachineDominatorTree>(); + const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); + const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>(); + + // First compute the nearest common dominator of all forward non-fallthrough + // predecessors so that we minimize the time that the BLOCK is on the stack, + // which reduces overall stack height. + MachineBasicBlock *Header = nullptr; + bool IsBranchedTo = false; + bool IsBrOnExn = false; + MachineInstr *BrOnExn = nullptr; + int MBBNumber = MBB.getNumber(); + for (MachineBasicBlock *Pred : MBB.predecessors()) { + if (Pred->getNumber() < MBBNumber) { + Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred; + if (explicitlyBranchesTo(Pred, &MBB)) { + IsBranchedTo = true; + if (Pred->getFirstTerminator()->getOpcode() == WebAssembly::BR_ON_EXN) { + IsBrOnExn = true; + assert(!BrOnExn && "There should be only one br_on_exn per block"); + BrOnExn = &*Pred->getFirstTerminator(); + } + } + } + } + if (!Header) + return; + if (!IsBranchedTo) + return; + + assert(&MBB != &MF.front() && "Header blocks shouldn't have predecessors"); + MachineBasicBlock *LayoutPred = MBB.getPrevNode(); + + // If the nearest common dominator is inside a more deeply nested context, + // walk out to the nearest scope which isn't more deeply nested. + for (MachineFunction::iterator I(LayoutPred), E(Header); I != E; --I) { + if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) { + if (ScopeTop->getNumber() > Header->getNumber()) { + // Skip over an intervening scope. + I = std::next(ScopeTop->getIterator()); + } else { + // We found a scope level at an appropriate depth. + Header = ScopeTop; + break; + } + } + } + + // Decide where in Header to put the BLOCK. + + // Instructions that should go before the BLOCK. + SmallPtrSet<const MachineInstr *, 4> BeforeSet; + // Instructions that should go after the BLOCK. + SmallPtrSet<const MachineInstr *, 4> AfterSet; + for (const auto &MI : *Header) { + // If there is a previously placed LOOP marker and the bottom block of the + // loop is above MBB, it should be after the BLOCK, because the loop is + // nested in this BLOCK. Otherwise it should be before the BLOCK. + if (MI.getOpcode() == WebAssembly::LOOP) { + auto *LoopBottom = BeginToEnd[&MI]->getParent()->getPrevNode(); + if (MBB.getNumber() > LoopBottom->getNumber()) + AfterSet.insert(&MI); +#ifndef NDEBUG + else + BeforeSet.insert(&MI); +#endif + } + + // All previously inserted BLOCK/TRY markers should be after the BLOCK + // because they are all nested blocks. + if (MI.getOpcode() == WebAssembly::BLOCK || + MI.getOpcode() == WebAssembly::TRY) + AfterSet.insert(&MI); + +#ifndef NDEBUG + // All END_(BLOCK|LOOP|TRY) markers should be before the BLOCK. + if (MI.getOpcode() == WebAssembly::END_BLOCK || + MI.getOpcode() == WebAssembly::END_LOOP || + MI.getOpcode() == WebAssembly::END_TRY) + BeforeSet.insert(&MI); +#endif + + // Terminators should go after the BLOCK. + if (MI.isTerminator()) + AfterSet.insert(&MI); + } + + // Local expression tree should go after the BLOCK. + for (auto I = Header->getFirstTerminator(), E = Header->begin(); I != E; + --I) { + if (std::prev(I)->isDebugInstr() || std::prev(I)->isPosition()) + continue; + if (WebAssembly::isChild(*std::prev(I), MFI)) + AfterSet.insert(&*std::prev(I)); + else + break; + } + + // Add the BLOCK. + + // 'br_on_exn' extracts exnref object and pushes variable number of values + // depending on its tag. For C++ exception, its a single i32 value, and the + // generated code will be in the form of: + // block i32 + // br_on_exn 0, $__cpp_exception + // rethrow + // end_block + WebAssembly::BlockType ReturnType = WebAssembly::BlockType::Void; + if (IsBrOnExn) { + const char *TagName = BrOnExn->getOperand(1).getSymbolName(); + if (std::strcmp(TagName, "__cpp_exception") != 0) + llvm_unreachable("Only C++ exception is supported"); + ReturnType = WebAssembly::BlockType::I32; + } + + auto InsertPos = getLatestInsertPos(Header, BeforeSet, AfterSet); + MachineInstr *Begin = + BuildMI(*Header, InsertPos, Header->findDebugLoc(InsertPos), + TII.get(WebAssembly::BLOCK)) + .addImm(int64_t(ReturnType)); + + // Decide where in Header to put the END_BLOCK. + BeforeSet.clear(); + AfterSet.clear(); + for (auto &MI : MBB) { +#ifndef NDEBUG + // END_BLOCK should precede existing LOOP and TRY markers. + if (MI.getOpcode() == WebAssembly::LOOP || + MI.getOpcode() == WebAssembly::TRY) + AfterSet.insert(&MI); +#endif + + // If there is a previously placed END_LOOP marker and the header of the + // loop is above this block's header, the END_LOOP should be placed after + // the BLOCK, because the loop contains this block. Otherwise the END_LOOP + // should be placed before the BLOCK. The same for END_TRY. + if (MI.getOpcode() == WebAssembly::END_LOOP || + MI.getOpcode() == WebAssembly::END_TRY) { + if (EndToBegin[&MI]->getParent()->getNumber() >= Header->getNumber()) + BeforeSet.insert(&MI); +#ifndef NDEBUG + else + AfterSet.insert(&MI); +#endif + } + } + + // Mark the end of the block. + InsertPos = getEarliestInsertPos(&MBB, BeforeSet, AfterSet); + MachineInstr *End = BuildMI(MBB, InsertPos, MBB.findPrevDebugLoc(InsertPos), + TII.get(WebAssembly::END_BLOCK)); + registerScope(Begin, End); + + // Track the farthest-spanning scope that ends at this point. + int Number = MBB.getNumber(); + if (!ScopeTops[Number] || + ScopeTops[Number]->getNumber() > Header->getNumber()) + ScopeTops[Number] = Header; +} + +/// Insert a LOOP marker for a loop starting at MBB (if it's a loop header). +void WebAssemblyCFGStackify::placeLoopMarker(MachineBasicBlock &MBB) { + MachineFunction &MF = *MBB.getParent(); + const auto &MLI = getAnalysis<MachineLoopInfo>(); + const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); + + MachineLoop *Loop = MLI.getLoopFor(&MBB); + if (!Loop || Loop->getHeader() != &MBB) + return; + + // The operand of a LOOP is the first block after the loop. If the loop is the + // bottom of the function, insert a dummy block at the end. + MachineBasicBlock *Bottom = WebAssembly::getBottom(Loop); + auto Iter = std::next(Bottom->getIterator()); + if (Iter == MF.end()) { + getAppendixBlock(MF); + Iter = std::next(Bottom->getIterator()); + } + MachineBasicBlock *AfterLoop = &*Iter; + + // Decide where in Header to put the LOOP. + SmallPtrSet<const MachineInstr *, 4> BeforeSet; + SmallPtrSet<const MachineInstr *, 4> AfterSet; + for (const auto &MI : MBB) { + // LOOP marker should be after any existing loop that ends here. Otherwise + // we assume the instruction belongs to the loop. + if (MI.getOpcode() == WebAssembly::END_LOOP) + BeforeSet.insert(&MI); +#ifndef NDEBUG + else + AfterSet.insert(&MI); +#endif + } + + // Mark the beginning of the loop. + auto InsertPos = getEarliestInsertPos(&MBB, BeforeSet, AfterSet); + MachineInstr *Begin = BuildMI(MBB, InsertPos, MBB.findDebugLoc(InsertPos), + TII.get(WebAssembly::LOOP)) + .addImm(int64_t(WebAssembly::BlockType::Void)); + + // Decide where in Header to put the END_LOOP. + BeforeSet.clear(); + AfterSet.clear(); +#ifndef NDEBUG + for (const auto &MI : MBB) + // Existing END_LOOP markers belong to parent loops of this loop + if (MI.getOpcode() == WebAssembly::END_LOOP) + AfterSet.insert(&MI); +#endif + + // Mark the end of the loop (using arbitrary debug location that branched to + // the loop end as its location). + InsertPos = getEarliestInsertPos(AfterLoop, BeforeSet, AfterSet); + DebugLoc EndDL = AfterLoop->pred_empty() + ? DebugLoc() + : (*AfterLoop->pred_rbegin())->findBranchDebugLoc(); + MachineInstr *End = + BuildMI(*AfterLoop, InsertPos, EndDL, TII.get(WebAssembly::END_LOOP)); + registerScope(Begin, End); + + assert((!ScopeTops[AfterLoop->getNumber()] || + ScopeTops[AfterLoop->getNumber()]->getNumber() < MBB.getNumber()) && + "With block sorting the outermost loop for a block should be first."); + if (!ScopeTops[AfterLoop->getNumber()]) + ScopeTops[AfterLoop->getNumber()] = &MBB; +} + +void WebAssemblyCFGStackify::placeTryMarker(MachineBasicBlock &MBB) { + assert(MBB.isEHPad()); + MachineFunction &MF = *MBB.getParent(); + auto &MDT = getAnalysis<MachineDominatorTree>(); + const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); + const auto &WEI = getAnalysis<WebAssemblyExceptionInfo>(); + const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>(); + + // Compute the nearest common dominator of all unwind predecessors + MachineBasicBlock *Header = nullptr; + int MBBNumber = MBB.getNumber(); + for (auto *Pred : MBB.predecessors()) { + if (Pred->getNumber() < MBBNumber) { + Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred; + assert(!explicitlyBranchesTo(Pred, &MBB) && + "Explicit branch to an EH pad!"); + } + } + if (!Header) + return; + + // If this try is at the bottom of the function, insert a dummy block at the + // end. + WebAssemblyException *WE = WEI.getExceptionFor(&MBB); + assert(WE); + MachineBasicBlock *Bottom = WebAssembly::getBottom(WE); + + auto Iter = std::next(Bottom->getIterator()); + if (Iter == MF.end()) { + getAppendixBlock(MF); + Iter = std::next(Bottom->getIterator()); + } + MachineBasicBlock *Cont = &*Iter; + + assert(Cont != &MF.front()); + MachineBasicBlock *LayoutPred = Cont->getPrevNode(); + + // If the nearest common dominator is inside a more deeply nested context, + // walk out to the nearest scope which isn't more deeply nested. + for (MachineFunction::iterator I(LayoutPred), E(Header); I != E; --I) { + if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) { + if (ScopeTop->getNumber() > Header->getNumber()) { + // Skip over an intervening scope. + I = std::next(ScopeTop->getIterator()); + } else { + // We found a scope level at an appropriate depth. + Header = ScopeTop; + break; + } + } + } + + // Decide where in Header to put the TRY. + + // Instructions that should go before the TRY. + SmallPtrSet<const MachineInstr *, 4> BeforeSet; + // Instructions that should go after the TRY. + SmallPtrSet<const MachineInstr *, 4> AfterSet; + for (const auto &MI : *Header) { + // If there is a previously placed LOOP marker and the bottom block of the + // loop is above MBB, it should be after the TRY, because the loop is nested + // in this TRY. Otherwise it should be before the TRY. + if (MI.getOpcode() == WebAssembly::LOOP) { + auto *LoopBottom = BeginToEnd[&MI]->getParent()->getPrevNode(); + if (MBB.getNumber() > LoopBottom->getNumber()) + AfterSet.insert(&MI); +#ifndef NDEBUG + else + BeforeSet.insert(&MI); +#endif + } + + // All previously inserted BLOCK/TRY markers should be after the TRY because + // they are all nested trys. + if (MI.getOpcode() == WebAssembly::BLOCK || + MI.getOpcode() == WebAssembly::TRY) + AfterSet.insert(&MI); + +#ifndef NDEBUG + // All END_(BLOCK/LOOP/TRY) markers should be before the TRY. + if (MI.getOpcode() == WebAssembly::END_BLOCK || + MI.getOpcode() == WebAssembly::END_LOOP || + MI.getOpcode() == WebAssembly::END_TRY) + BeforeSet.insert(&MI); +#endif + + // Terminators should go after the TRY. + if (MI.isTerminator()) + AfterSet.insert(&MI); + } + + // If Header unwinds to MBB (= Header contains 'invoke'), the try block should + // contain the call within it. So the call should go after the TRY. The + // exception is when the header's terminator is a rethrow instruction, in + // which case that instruction, not a call instruction before it, is gonna + // throw. + MachineInstr *ThrowingCall = nullptr; + if (MBB.isPredecessor(Header)) { + auto TermPos = Header->getFirstTerminator(); + if (TermPos == Header->end() || + TermPos->getOpcode() != WebAssembly::RETHROW) { + for (auto &MI : reverse(*Header)) { + if (MI.isCall()) { + AfterSet.insert(&MI); + ThrowingCall = &MI; + // Possibly throwing calls are usually wrapped by EH_LABEL + // instructions. We don't want to split them and the call. + if (MI.getIterator() != Header->begin() && + std::prev(MI.getIterator())->isEHLabel()) { + AfterSet.insert(&*std::prev(MI.getIterator())); + ThrowingCall = &*std::prev(MI.getIterator()); + } + break; + } + } + } + } + + // Local expression tree should go after the TRY. + // For BLOCK placement, we start the search from the previous instruction of a + // BB's terminator, but in TRY's case, we should start from the previous + // instruction of a call that can throw, or a EH_LABEL that precedes the call, + // because the return values of the call's previous instructions can be + // stackified and consumed by the throwing call. + auto SearchStartPt = ThrowingCall ? MachineBasicBlock::iterator(ThrowingCall) + : Header->getFirstTerminator(); + for (auto I = SearchStartPt, E = Header->begin(); I != E; --I) { + if (std::prev(I)->isDebugInstr() || std::prev(I)->isPosition()) + continue; + if (WebAssembly::isChild(*std::prev(I), MFI)) + AfterSet.insert(&*std::prev(I)); + else + break; + } + + // Add the TRY. + auto InsertPos = getLatestInsertPos(Header, BeforeSet, AfterSet); + MachineInstr *Begin = + BuildMI(*Header, InsertPos, Header->findDebugLoc(InsertPos), + TII.get(WebAssembly::TRY)) + .addImm(int64_t(WebAssembly::BlockType::Void)); + + // Decide where in Header to put the END_TRY. + BeforeSet.clear(); + AfterSet.clear(); + for (const auto &MI : *Cont) { +#ifndef NDEBUG + // END_TRY should precede existing LOOP and BLOCK markers. + if (MI.getOpcode() == WebAssembly::LOOP || + MI.getOpcode() == WebAssembly::BLOCK) + AfterSet.insert(&MI); + + // All END_TRY markers placed earlier belong to exceptions that contains + // this one. + if (MI.getOpcode() == WebAssembly::END_TRY) + AfterSet.insert(&MI); +#endif + + // If there is a previously placed END_LOOP marker and its header is after + // where TRY marker is, this loop is contained within the 'catch' part, so + // the END_TRY marker should go after that. Otherwise, the whole try-catch + // is contained within this loop, so the END_TRY should go before that. + if (MI.getOpcode() == WebAssembly::END_LOOP) { + // For a LOOP to be after TRY, LOOP's BB should be after TRY's BB; if they + // are in the same BB, LOOP is always before TRY. + if (EndToBegin[&MI]->getParent()->getNumber() > Header->getNumber()) + BeforeSet.insert(&MI); +#ifndef NDEBUG + else + AfterSet.insert(&MI); +#endif + } + + // It is not possible for an END_BLOCK to be already in this block. + } + + // Mark the end of the TRY. + InsertPos = getEarliestInsertPos(Cont, BeforeSet, AfterSet); + MachineInstr *End = + BuildMI(*Cont, InsertPos, Bottom->findBranchDebugLoc(), + TII.get(WebAssembly::END_TRY)); + registerTryScope(Begin, End, &MBB); + + // Track the farthest-spanning scope that ends at this point. We create two + // mappings: (BB with 'end_try' -> BB with 'try') and (BB with 'catch' -> BB + // with 'try'). We need to create 'catch' -> 'try' mapping here too because + // markers should not span across 'catch'. For example, this should not + // happen: + // + // try + // block --| (X) + // catch | + // end_block --| + // end_try + for (int Number : {Cont->getNumber(), MBB.getNumber()}) { + if (!ScopeTops[Number] || + ScopeTops[Number]->getNumber() > Header->getNumber()) + ScopeTops[Number] = Header; + } +} + +void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) { + const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); + + // When there is an unconditional branch right before a catch instruction and + // it branches to the end of end_try marker, we don't need the branch, because + // it there is no exception, the control flow transfers to that point anyway. + // bb0: + // try + // ... + // br bb2 <- Not necessary + // bb1: + // catch + // ... + // bb2: + // end + for (auto &MBB : MF) { + if (!MBB.isEHPad()) + continue; + + MachineBasicBlock *TBB = nullptr, *FBB = nullptr; + SmallVector<MachineOperand, 4> Cond; + MachineBasicBlock *EHPadLayoutPred = MBB.getPrevNode(); + MachineBasicBlock *Cont = BeginToEnd[EHPadToTry[&MBB]]->getParent(); + bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond); + if (Analyzable && ((Cond.empty() && TBB && TBB == Cont) || + (!Cond.empty() && FBB && FBB == Cont))) + TII.removeBranch(*EHPadLayoutPred); + } + + // When there are block / end_block markers that overlap with try / end_try + // markers, and the block and try markers' return types are the same, the + // block /end_block markers are not necessary, because try / end_try markers + // also can serve as boundaries for branches. + // block <- Not necessary + // try + // ... + // catch + // ... + // end + // end <- Not necessary + SmallVector<MachineInstr *, 32> ToDelete; + for (auto &MBB : MF) { + for (auto &MI : MBB) { + if (MI.getOpcode() != WebAssembly::TRY) + continue; + + MachineInstr *Try = &MI, *EndTry = BeginToEnd[Try]; + MachineBasicBlock *TryBB = Try->getParent(); + MachineBasicBlock *Cont = EndTry->getParent(); + int64_t RetType = Try->getOperand(0).getImm(); + for (auto B = Try->getIterator(), E = std::next(EndTry->getIterator()); + B != TryBB->begin() && E != Cont->end() && + std::prev(B)->getOpcode() == WebAssembly::BLOCK && + E->getOpcode() == WebAssembly::END_BLOCK && + std::prev(B)->getOperand(0).getImm() == RetType; + --B, ++E) { + ToDelete.push_back(&*std::prev(B)); + ToDelete.push_back(&*E); + } + } + } + for (auto *MI : ToDelete) { + if (MI->getOpcode() == WebAssembly::BLOCK) + unregisterScope(MI); + MI->eraseFromParent(); + } +} + +// When MBB is split into MBB and Split, we should unstackify defs in MBB that +// have their uses in Split. +static void unstackifyVRegsUsedInSplitBB(MachineBasicBlock &MBB, + MachineBasicBlock &Split, + WebAssemblyFunctionInfo &MFI, + MachineRegisterInfo &MRI) { + for (auto &MI : Split) { + for (auto &MO : MI.explicit_uses()) { + if (!MO.isReg() || Register::isPhysicalRegister(MO.getReg())) + continue; + if (MachineInstr *Def = MRI.getUniqueVRegDef(MO.getReg())) + if (Def->getParent() == &MBB) + MFI.unstackifyVReg(MO.getReg()); + } + } +} + +bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) { + const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); + auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>(); + MachineRegisterInfo &MRI = MF.getRegInfo(); + + // Linearizing the control flow by placing TRY / END_TRY markers can create + // mismatches in unwind destinations. There are two kinds of mismatches we + // try to solve here. + + // 1. When an instruction may throw, but the EH pad it will unwind to can be + // different from the original CFG. + // + // Example: we have the following CFG: + // bb0: + // call @foo (if it throws, unwind to bb2) + // bb1: + // call @bar (if it throws, unwind to bb3) + // bb2 (ehpad): + // catch + // ... + // bb3 (ehpad) + // catch + // handler body + // + // And the CFG is sorted in this order. Then after placing TRY markers, it + // will look like: (BB markers are omitted) + // try $label1 + // try + // call @foo + // call @bar (if it throws, unwind to bb3) + // catch <- ehpad (bb2) + // ... + // end_try + // catch <- ehpad (bb3) + // handler body + // end_try + // + // Now if bar() throws, it is going to end up ip in bb2, not bb3, where it + // is supposed to end up. We solve this problem by + // a. Split the target unwind EH pad (here bb3) so that the handler body is + // right after 'end_try', which means we extract the handler body out of + // the catch block. We do this because this handler body should be + // somewhere branch-eable from the inner scope. + // b. Wrap the call that has an incorrect unwind destination ('call @bar' + // here) with a nested try/catch/end_try scope, and within the new catch + // block, branches to the handler body. + // c. Place a branch after the newly inserted nested end_try so it can bypass + // the handler body, which is now outside of a catch block. + // + // The result will like as follows. (new: a) means this instruction is newly + // created in the process of doing 'a' above. + // + // block $label0 (new: placeBlockMarker) + // try $label1 + // try + // call @foo + // try (new: b) + // call @bar + // catch (new: b) + // local.set n / drop (new: b) + // br $label1 (new: b) + // end_try (new: b) + // catch <- ehpad (bb2) + // end_try + // br $label0 (new: c) + // catch <- ehpad (bb3) + // end_try (hoisted: a) + // handler body + // end_block (new: placeBlockMarker) + // + // Note that the new wrapping block/end_block will be generated later in + // placeBlockMarker. + // + // TODO Currently local.set and local.gets are generated to move exnref value + // created by catches. That's because we don't support yielding values from a + // block in LLVM machine IR yet, even though it is supported by wasm. Delete + // unnecessary local.get/local.sets once yielding values from a block is + // supported. The full EH spec requires multi-value support to do this, but + // for C++ we don't yet need it because we only throw a single i32. + // + // --- + // 2. The same as 1, but in this case an instruction unwinds to a caller + // function and not another EH pad. + // + // Example: we have the following CFG: + // bb0: + // call @foo (if it throws, unwind to bb2) + // bb1: + // call @bar (if it throws, unwind to caller) + // bb2 (ehpad): + // catch + // ... + // + // And the CFG is sorted in this order. Then after placing TRY markers, it + // will look like: + // try + // call @foo + // call @bar (if it throws, unwind to caller) + // catch <- ehpad (bb2) + // ... + // end_try + // + // Now if bar() throws, it is going to end up ip in bb2, when it is supposed + // throw up to the caller. + // We solve this problem by + // a. Create a new 'appendix' BB at the end of the function and put a single + // 'rethrow' instruction (+ local.get) in there. + // b. Wrap the call that has an incorrect unwind destination ('call @bar' + // here) with a nested try/catch/end_try scope, and within the new catch + // block, branches to the new appendix block. + // + // block $label0 (new: placeBlockMarker) + // try + // call @foo + // try (new: b) + // call @bar + // catch (new: b) + // local.set n (new: b) + // br $label0 (new: b) + // end_try (new: b) + // catch <- ehpad (bb2) + // ... + // end_try + // ... + // end_block (new: placeBlockMarker) + // local.get n (new: a) <- appendix block + // rethrow (new: a) + // + // In case there are multiple calls in a BB that may throw to the caller, they + // can be wrapped together in one nested try scope. (In 1, this couldn't + // happen, because may-throwing instruction there had an unwind destination, + // i.e., it was an invoke before, and there could be only one invoke within a + // BB.) + + SmallVector<const MachineBasicBlock *, 8> EHPadStack; + // Range of intructions to be wrapped in a new nested try/catch + using TryRange = std::pair<MachineInstr *, MachineInstr *>; + // In original CFG, <unwind destination BB, a vector of try ranges> + DenseMap<MachineBasicBlock *, SmallVector<TryRange, 4>> UnwindDestToTryRanges; + // In new CFG, <destination to branch to, a vector of try ranges> + DenseMap<MachineBasicBlock *, SmallVector<TryRange, 4>> BrDestToTryRanges; + // In new CFG, <destination to branch to, register containing exnref> + DenseMap<MachineBasicBlock *, unsigned> BrDestToExnReg; + + // Gather possibly throwing calls (i.e., previously invokes) whose current + // unwind destination is not the same as the original CFG. + for (auto &MBB : reverse(MF)) { + bool SeenThrowableInstInBB = false; + for (auto &MI : reverse(MBB)) { + if (MI.getOpcode() == WebAssembly::TRY) + EHPadStack.pop_back(); + else if (MI.getOpcode() == WebAssembly::CATCH) + EHPadStack.push_back(MI.getParent()); + + // In this loop we only gather calls that have an EH pad to unwind. So + // there will be at most 1 such call (= invoke) in a BB, so after we've + // seen one, we can skip the rest of BB. Also if MBB has no EH pad + // successor or MI does not throw, this is not an invoke. + if (SeenThrowableInstInBB || !MBB.hasEHPadSuccessor() || + !WebAssembly::mayThrow(MI)) + continue; + SeenThrowableInstInBB = true; + + // If the EH pad on the stack top is where this instruction should unwind + // next, we're good. + MachineBasicBlock *UnwindDest = nullptr; + for (auto *Succ : MBB.successors()) { + if (Succ->isEHPad()) { + UnwindDest = Succ; + break; + } + } + if (EHPadStack.back() == UnwindDest) + continue; + + // If not, record the range. + UnwindDestToTryRanges[UnwindDest].push_back(TryRange(&MI, &MI)); + } + } + + assert(EHPadStack.empty()); + + // Gather possibly throwing calls that are supposed to unwind up to the caller + // if they throw, but currently unwind to an incorrect destination. Unlike the + // loop above, there can be multiple calls within a BB that unwind to the + // caller, which we should group together in a range. + bool NeedAppendixBlock = false; + for (auto &MBB : reverse(MF)) { + MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr; // inclusive + for (auto &MI : reverse(MBB)) { + if (MI.getOpcode() == WebAssembly::TRY) + EHPadStack.pop_back(); + else if (MI.getOpcode() == WebAssembly::CATCH) + EHPadStack.push_back(MI.getParent()); + + // If MBB has an EH pad successor, this inst does not unwind to caller. + if (MBB.hasEHPadSuccessor()) + continue; + + // We wrap up the current range when we see a marker even if we haven't + // finished a BB. + if (RangeEnd && WebAssembly::isMarker(MI.getOpcode())) { + NeedAppendixBlock = true; + // Record the range. nullptr here means the unwind destination is the + // caller. + UnwindDestToTryRanges[nullptr].push_back( + TryRange(RangeBegin, RangeEnd)); + RangeBegin = RangeEnd = nullptr; // Reset range pointers + } + + // If EHPadStack is empty, that means it is correctly unwind to caller if + // it throws, so we're good. If MI does not throw, we're good too. + if (EHPadStack.empty() || !WebAssembly::mayThrow(MI)) + continue; + + // We found an instruction that unwinds to the caller but currently has an + // incorrect unwind destination. Create a new range or increment the + // currently existing range. + if (!RangeEnd) + RangeBegin = RangeEnd = &MI; + else + RangeBegin = &MI; + } + + if (RangeEnd) { + NeedAppendixBlock = true; + // Record the range. nullptr here means the unwind destination is the + // caller. + UnwindDestToTryRanges[nullptr].push_back(TryRange(RangeBegin, RangeEnd)); + RangeBegin = RangeEnd = nullptr; // Reset range pointers + } + } + + assert(EHPadStack.empty()); + // We don't have any unwind destination mismatches to resolve. + if (UnwindDestToTryRanges.empty()) + return false; + + // If we found instructions that should unwind to the caller but currently + // have incorrect unwind destination, we create an appendix block at the end + // of the function with a local.get and a rethrow instruction. + if (NeedAppendixBlock) { + auto *AppendixBB = getAppendixBlock(MF); + Register ExnReg = MRI.createVirtualRegister(&WebAssembly::EXNREFRegClass); + BuildMI(AppendixBB, DebugLoc(), TII.get(WebAssembly::RETHROW)) + .addReg(ExnReg); + // These instruction ranges should branch to this appendix BB. + for (auto Range : UnwindDestToTryRanges[nullptr]) + BrDestToTryRanges[AppendixBB].push_back(Range); + BrDestToExnReg[AppendixBB] = ExnReg; + } + + // We loop through unwind destination EH pads that are targeted from some + // inner scopes. Because these EH pads are destination of more than one scope + // now, we split them so that the handler body is after 'end_try'. + // - Before + // ehpad: + // catch + // local.set n / drop + // handler body + // ... + // cont: + // end_try + // + // - After + // ehpad: + // catch + // local.set n / drop + // brdest: (new) + // end_try (hoisted from 'cont' BB) + // handler body (taken from 'ehpad') + // ... + // cont: + for (auto &P : UnwindDestToTryRanges) { + NumUnwindMismatches += P.second.size(); + + // This means the destination is the appendix BB, which was separately + // handled above. + if (!P.first) + continue; + + MachineBasicBlock *EHPad = P.first; + + // Find 'catch' and 'local.set' or 'drop' instruction that follows the + // 'catch'. If -wasm-disable-explicit-locals is not set, 'catch' should be + // always followed by either 'local.set' or a 'drop', because 'br_on_exn' is + // generated after 'catch' in LateEHPrepare and we don't support blocks + // taking values yet. + MachineInstr *Catch = nullptr; + unsigned ExnReg = 0; + for (auto &MI : *EHPad) { + switch (MI.getOpcode()) { + case WebAssembly::CATCH: + Catch = &MI; + ExnReg = Catch->getOperand(0).getReg(); + break; + } + } + assert(Catch && "EH pad does not have a catch"); + assert(ExnReg != 0 && "Invalid register"); + + auto SplitPos = std::next(Catch->getIterator()); + + // Create a new BB that's gonna be the destination for branches from the + // inner mismatched scope. + MachineInstr *BeginTry = EHPadToTry[EHPad]; + MachineInstr *EndTry = BeginToEnd[BeginTry]; + MachineBasicBlock *Cont = EndTry->getParent(); + auto *BrDest = MF.CreateMachineBasicBlock(); + MF.insert(std::next(EHPad->getIterator()), BrDest); + // Hoist up the existing 'end_try'. + BrDest->insert(BrDest->end(), EndTry->removeFromParent()); + // Take out the handler body from EH pad to the new branch destination BB. + BrDest->splice(BrDest->end(), EHPad, SplitPos, EHPad->end()); + unstackifyVRegsUsedInSplitBB(*EHPad, *BrDest, MFI, MRI); + // Fix predecessor-successor relationship. + BrDest->transferSuccessors(EHPad); + EHPad->addSuccessor(BrDest); + + // All try ranges that were supposed to unwind to this EH pad now have to + // branch to this new branch dest BB. + for (auto Range : UnwindDestToTryRanges[EHPad]) + BrDestToTryRanges[BrDest].push_back(Range); + BrDestToExnReg[BrDest] = ExnReg; + + // In case we fall through to the continuation BB after the catch block, we + // now have to add a branch to it. + // - Before + // try + // ... + // (falls through to 'cont') + // catch + // handler body + // end + // <-- cont + // + // - After + // try + // ... + // br %cont (new) + // catch + // end + // handler body + // <-- cont + MachineBasicBlock *EHPadLayoutPred = &*std::prev(EHPad->getIterator()); + MachineBasicBlock *TBB = nullptr, *FBB = nullptr; + SmallVector<MachineOperand, 4> Cond; + bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond); + if (Analyzable && !TBB && !FBB) { + DebugLoc DL = EHPadLayoutPred->empty() + ? DebugLoc() + : EHPadLayoutPred->rbegin()->getDebugLoc(); + BuildMI(EHPadLayoutPred, DL, TII.get(WebAssembly::BR)).addMBB(Cont); + } + } + + // For possibly throwing calls whose unwind destinations are currently + // incorrect because of CFG linearization, we wrap them with a nested + // try/catch/end_try, and within the new catch block, we branch to the correct + // handler. + // - Before + // mbb: + // call @foo <- Unwind destination mismatch! + // ehpad: + // ... + // + // - After + // mbb: + // try (new) + // call @foo + // nested-ehpad: (new) + // catch (new) + // local.set n / drop (new) + // br %brdest (new) + // nested-end: (new) + // end_try (new) + // ehpad: + // ... + for (auto &P : BrDestToTryRanges) { + MachineBasicBlock *BrDest = P.first; + auto &TryRanges = P.second; + unsigned ExnReg = BrDestToExnReg[BrDest]; + + for (auto Range : TryRanges) { + MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr; + std::tie(RangeBegin, RangeEnd) = Range; + auto *MBB = RangeBegin->getParent(); + + // Include possible EH_LABELs in the range + if (RangeBegin->getIterator() != MBB->begin() && + std::prev(RangeBegin->getIterator())->isEHLabel()) + RangeBegin = &*std::prev(RangeBegin->getIterator()); + if (std::next(RangeEnd->getIterator()) != MBB->end() && + std::next(RangeEnd->getIterator())->isEHLabel()) + RangeEnd = &*std::next(RangeEnd->getIterator()); + + MachineBasicBlock *EHPad = nullptr; + for (auto *Succ : MBB->successors()) { + if (Succ->isEHPad()) { + EHPad = Succ; + break; + } + } + + // Create the nested try instruction. + MachineInstr *NestedTry = + BuildMI(*MBB, *RangeBegin, RangeBegin->getDebugLoc(), + TII.get(WebAssembly::TRY)) + .addImm(int64_t(WebAssembly::BlockType::Void)); + + // Create the nested EH pad and fill instructions in. + MachineBasicBlock *NestedEHPad = MF.CreateMachineBasicBlock(); + MF.insert(std::next(MBB->getIterator()), NestedEHPad); + NestedEHPad->setIsEHPad(); + NestedEHPad->setIsEHScopeEntry(); + BuildMI(NestedEHPad, RangeEnd->getDebugLoc(), TII.get(WebAssembly::CATCH), + ExnReg); + BuildMI(NestedEHPad, RangeEnd->getDebugLoc(), TII.get(WebAssembly::BR)) + .addMBB(BrDest); + + // Create the nested continuation BB and end_try instruction. + MachineBasicBlock *NestedCont = MF.CreateMachineBasicBlock(); + MF.insert(std::next(NestedEHPad->getIterator()), NestedCont); + MachineInstr *NestedEndTry = + BuildMI(*NestedCont, NestedCont->begin(), RangeEnd->getDebugLoc(), + TII.get(WebAssembly::END_TRY)); + // In case MBB has more instructions after the try range, move them to the + // new nested continuation BB. + NestedCont->splice(NestedCont->end(), MBB, + std::next(RangeEnd->getIterator()), MBB->end()); + unstackifyVRegsUsedInSplitBB(*MBB, *NestedCont, MFI, MRI); + registerTryScope(NestedTry, NestedEndTry, NestedEHPad); + + // Fix predecessor-successor relationship. + NestedCont->transferSuccessors(MBB); + if (EHPad) + NestedCont->removeSuccessor(EHPad); + MBB->addSuccessor(NestedEHPad); + MBB->addSuccessor(NestedCont); + NestedEHPad->addSuccessor(BrDest); + } + } + + // Renumber BBs and recalculate ScopeTop info because new BBs might have been + // created and inserted above. + MF.RenumberBlocks(); + ScopeTops.clear(); + ScopeTops.resize(MF.getNumBlockIDs()); + for (auto &MBB : reverse(MF)) { + for (auto &MI : reverse(MBB)) { + if (ScopeTops[MBB.getNumber()]) + break; + switch (MI.getOpcode()) { + case WebAssembly::END_BLOCK: + case WebAssembly::END_LOOP: + case WebAssembly::END_TRY: + ScopeTops[MBB.getNumber()] = EndToBegin[&MI]->getParent(); + break; + case WebAssembly::CATCH: + ScopeTops[MBB.getNumber()] = EHPadToTry[&MBB]->getParent(); + break; + } + } + } + + // Recompute the dominator tree. + getAnalysis<MachineDominatorTree>().runOnMachineFunction(MF); + + // Place block markers for newly added branches. + SmallVector <MachineBasicBlock *, 8> BrDests; + for (auto &P : BrDestToTryRanges) + BrDests.push_back(P.first); + llvm::sort(BrDests, + [&](const MachineBasicBlock *A, const MachineBasicBlock *B) { + auto ANum = A->getNumber(); + auto BNum = B->getNumber(); + return ANum < BNum; + }); + for (auto *Dest : BrDests) + placeBlockMarker(*Dest); + + return true; +} + +static unsigned +getDepth(const SmallVectorImpl<const MachineBasicBlock *> &Stack, + const MachineBasicBlock *MBB) { + unsigned Depth = 0; + for (auto X : reverse(Stack)) { + if (X == MBB) + break; + ++Depth; + } + assert(Depth < Stack.size() && "Branch destination should be in scope"); + return Depth; +} + +/// In normal assembly languages, when the end of a function is unreachable, +/// because the function ends in an infinite loop or a noreturn call or similar, +/// it isn't necessary to worry about the function return type at the end of +/// the function, because it's never reached. However, in WebAssembly, blocks +/// that end at the function end need to have a return type signature that +/// matches the function signature, even though it's unreachable. This function +/// checks for such cases and fixes up the signatures. +void WebAssemblyCFGStackify::fixEndsAtEndOfFunction(MachineFunction &MF) { + const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>(); + + if (MFI.getResults().empty()) + return; + + // MCInstLower will add the proper types to multivalue signatures based on the + // function return type + WebAssembly::BlockType RetType = + MFI.getResults().size() > 1 + ? WebAssembly::BlockType::Multivalue + : WebAssembly::BlockType( + WebAssembly::toValType(MFI.getResults().front())); + + for (MachineBasicBlock &MBB : reverse(MF)) { + for (MachineInstr &MI : reverse(MBB)) { + if (MI.isPosition() || MI.isDebugInstr()) + continue; + switch (MI.getOpcode()) { + case WebAssembly::END_BLOCK: + case WebAssembly::END_LOOP: + case WebAssembly::END_TRY: + EndToBegin[&MI]->getOperand(0).setImm(int32_t(RetType)); + continue; + default: + // Something other than an `end`. We're done. + return; + } + } + } +} + +// WebAssembly functions end with an end instruction, as if the function body +// were a block. +static void appendEndToFunction(MachineFunction &MF, + const WebAssemblyInstrInfo &TII) { + BuildMI(MF.back(), MF.back().end(), + MF.back().findPrevDebugLoc(MF.back().end()), + TII.get(WebAssembly::END_FUNCTION)); +} + +/// Insert LOOP/TRY/BLOCK markers at appropriate places. +void WebAssemblyCFGStackify::placeMarkers(MachineFunction &MF) { + // We allocate one more than the number of blocks in the function to + // accommodate for the possible fake block we may insert at the end. + ScopeTops.resize(MF.getNumBlockIDs() + 1); + // Place the LOOP for MBB if MBB is the header of a loop. + for (auto &MBB : MF) + placeLoopMarker(MBB); + + const MCAsmInfo *MCAI = MF.getTarget().getMCAsmInfo(); + for (auto &MBB : MF) { + if (MBB.isEHPad()) { + // Place the TRY for MBB if MBB is the EH pad of an exception. + if (MCAI->getExceptionHandlingType() == ExceptionHandling::Wasm && + MF.getFunction().hasPersonalityFn()) + placeTryMarker(MBB); + } else { + // Place the BLOCK for MBB if MBB is branched to from above. + placeBlockMarker(MBB); + } + } + // Fix mismatches in unwind destinations induced by linearizing the code. + if (MCAI->getExceptionHandlingType() == ExceptionHandling::Wasm && + MF.getFunction().hasPersonalityFn()) + fixUnwindMismatches(MF); +} + +void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) { + // Now rewrite references to basic blocks to be depth immediates. + SmallVector<const MachineBasicBlock *, 8> Stack; + for (auto &MBB : reverse(MF)) { + for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) { + MachineInstr &MI = *I; + switch (MI.getOpcode()) { + case WebAssembly::BLOCK: + case WebAssembly::TRY: + assert(ScopeTops[Stack.back()->getNumber()]->getNumber() <= + MBB.getNumber() && + "Block/try marker should be balanced"); + Stack.pop_back(); + break; + + case WebAssembly::LOOP: + assert(Stack.back() == &MBB && "Loop top should be balanced"); + Stack.pop_back(); + break; + + case WebAssembly::END_BLOCK: + case WebAssembly::END_TRY: + Stack.push_back(&MBB); + break; + + case WebAssembly::END_LOOP: + Stack.push_back(EndToBegin[&MI]->getParent()); + break; + + default: + if (MI.isTerminator()) { + // Rewrite MBB operands to be depth immediates. + SmallVector<MachineOperand, 4> Ops(MI.operands()); + while (MI.getNumOperands() > 0) + MI.RemoveOperand(MI.getNumOperands() - 1); + for (auto MO : Ops) { + if (MO.isMBB()) + MO = MachineOperand::CreateImm(getDepth(Stack, MO.getMBB())); + MI.addOperand(MF, MO); + } + } + break; + } + } + } + assert(Stack.empty() && "Control flow should be balanced"); +} + +void WebAssemblyCFGStackify::releaseMemory() { + ScopeTops.clear(); + BeginToEnd.clear(); + EndToBegin.clear(); + TryToEHPad.clear(); + EHPadToTry.clear(); + AppendixBB = nullptr; +} + +bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) { + LLVM_DEBUG(dbgs() << "********** CFG Stackifying **********\n" + "********** Function: " + << MF.getName() << '\n'); + const MCAsmInfo *MCAI = MF.getTarget().getMCAsmInfo(); + + releaseMemory(); + + // Liveness is not tracked for VALUE_STACK physreg. + MF.getRegInfo().invalidateLiveness(); + + // Place the BLOCK/LOOP/TRY markers to indicate the beginnings of scopes. + placeMarkers(MF); + + // Remove unnecessary instructions possibly introduced by try/end_trys. + if (MCAI->getExceptionHandlingType() == ExceptionHandling::Wasm && + MF.getFunction().hasPersonalityFn()) + removeUnnecessaryInstrs(MF); + + // Convert MBB operands in terminators to relative depth immediates. + rewriteDepthImmediates(MF); + + // Fix up block/loop/try signatures at the end of the function to conform to + // WebAssembly's rules. + fixEndsAtEndOfFunction(MF); + + // Add an end instruction at the end of the function body. + const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo(); + if (!MF.getSubtarget<WebAssemblySubtarget>() + .getTargetTriple() + .isOSBinFormatELF()) + appendEndToFunction(MF, TII); + + MF.getInfo<WebAssemblyFunctionInfo>()->setCFGStackified(); + return true; +} |