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[Windows] Replace TrapUnreachable with an int3 insertion pass
This is an alternative to D66980, which was reverted. Instead of inserting a pseudo instruction that optionally expands to nothing, add a pass that inserts int3 when appropriate after basic block layout. Reviewers: hans Differential Revision: https://reviews.llvm.org/D67201 llvm-svn: 371466
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,108 @@ | ||
| //===----- X86AvoidTrailingCall.cpp - Insert int3 after trailing calls ----===// | ||
| // | ||
| // 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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // The Windows x64 unwinder has trouble unwinding the stack when a return | ||
| // address points to the end of the function. This pass maintains the invariant | ||
| // that every return address is inside the bounds of its parent function or | ||
| // funclet by inserting int3 if the last instruction would otherwise be a call. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "X86.h" | ||
| #include "X86InstrInfo.h" | ||
| #include "X86Subtarget.h" | ||
| #include "llvm/CodeGen/MachineInstrBuilder.h" | ||
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| #define DEBUG_TYPE "x86-avoid-trailing-call" | ||
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| using namespace llvm; | ||
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| namespace { | ||
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| class X86AvoidTrailingCallPass : public MachineFunctionPass { | ||
| public: | ||
| X86AvoidTrailingCallPass() : MachineFunctionPass(ID) {} | ||
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| bool runOnMachineFunction(MachineFunction &MF) override; | ||
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| private: | ||
| StringRef getPassName() const override { | ||
| return "X86 avoid trailing call pass"; | ||
| } | ||
| static char ID; | ||
| }; | ||
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| char X86AvoidTrailingCallPass::ID = 0; | ||
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| } // end anonymous namespace | ||
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| FunctionPass *llvm::createX86AvoidTrailingCallPass() { | ||
| return new X86AvoidTrailingCallPass(); | ||
| } | ||
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| // A real instruction is a non-meta, non-pseudo instruction. Some pseudos | ||
| // expand to nothing, and some expand to code. This logic conservatively assumes | ||
| // they might expand to nothing. | ||
| static bool isRealInstruction(MachineInstr &MI) { | ||
| return !MI.isPseudo() && !MI.isMetaInstruction(); | ||
| } | ||
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| // Return true if this is a call instruction, but not a tail call. | ||
| static bool isCallInstruction(const MachineInstr &MI) { | ||
| return MI.isCall() && !MI.isReturn(); | ||
| } | ||
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| bool X86AvoidTrailingCallPass::runOnMachineFunction(MachineFunction &MF) { | ||
| const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>(); | ||
| const X86InstrInfo &TII = *STI.getInstrInfo(); | ||
| assert(STI.isTargetWin64() && "pass only runs on Win64"); | ||
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| // FIXME: Perhaps this pass should also replace SEH_Epilogue by inserting nops | ||
| // before epilogues. | ||
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| bool Changed = false; | ||
| for (MachineBasicBlock &MBB : MF) { | ||
| // Look for basic blocks that precede funclet entries or are at the end of | ||
| // the function. | ||
| MachineBasicBlock *NextMBB = MBB.getNextNode(); | ||
| if (NextMBB && !NextMBB->isEHFuncletEntry()) | ||
| continue; | ||
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| // Find the last real instruction in this block, or previous blocks if this | ||
| // block is empty. | ||
| MachineBasicBlock::reverse_iterator LastRealInstr; | ||
| for (MachineBasicBlock &RMBB : | ||
| make_range(MBB.getReverseIterator(), MF.rend())) { | ||
| LastRealInstr = llvm::find_if(reverse(RMBB), isRealInstruction); | ||
| if (LastRealInstr != RMBB.rend()) | ||
| break; | ||
| } | ||
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| // Do nothing if this function or funclet has no instructions. | ||
| if (LastRealInstr == MF.begin()->rend()) | ||
| continue; | ||
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| // If this is a call instruction, insert int3 right after it with the same | ||
| // DebugLoc. Convert back to a forward iterator and advance the insertion | ||
| // position once. | ||
| if (isCallInstruction(*LastRealInstr)) { | ||
| LLVM_DEBUG({ | ||
| dbgs() << "inserting int3 after trailing call instruction:\n"; | ||
| LastRealInstr->dump(); | ||
| dbgs() << '\n'; | ||
| }); | ||
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| MachineBasicBlock::iterator MBBI = std::next(LastRealInstr.getReverse()); | ||
| BuildMI(*LastRealInstr->getParent(), MBBI, LastRealInstr->getDebugLoc(), | ||
| TII.get(X86::INT3)); | ||
| Changed = true; | ||
| } | ||
| } | ||
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| return Changed; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
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@@ -15,7 +15,7 @@ entry: | |
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| ; CHECK-LABEL: f: | ||
| ; WIN32: nop | ||
| ; WIN64: ud2 | ||
| ; WIN64: nop | ||
| ; LINUX-NOT: nop | ||
| ; LINUX-NOT: ud2 | ||
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