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[RISCV] Add additional fence for amocas when required by recent ABI c…
…hange (llvm#101023) A recent atomics ABI change / fix requires that for the "A6C" and A6S" atomics ABIs (i.e. both of those supported by LLVM currently), an additional fence is inserted for an atomic_compare_exchange with seq_cst failure ordering. <riscv-non-isa/riscv-elf-psabi-doc#445> This isn't trivial to support through the hooks used by AtomicExpandPass because that pass assumes that when fences are inserted, the original atomics ordering information can be removed from the instruction. Rather than try to change and complicate that API, this patch implements the needed fence insertion through a small special purpose pass.
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| //===----- RISCVZacasABIFix.cpp -------------------------------------------===// | ||
| // | ||
| // 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 implements a fence insertion for an atomic cmpxchg in a case that | ||
| // isn't easy to do with the current AtomicExpandPass hooks API. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "RISCV.h" | ||
| #include "RISCVTargetMachine.h" | ||
| #include "llvm/ADT/Statistic.h" | ||
| #include "llvm/Analysis/ValueTracking.h" | ||
| #include "llvm/CodeGen/TargetPassConfig.h" | ||
| #include "llvm/IR/Dominators.h" | ||
| #include "llvm/IR/IRBuilder.h" | ||
| #include "llvm/IR/InstVisitor.h" | ||
| #include "llvm/IR/Intrinsics.h" | ||
| #include "llvm/IR/IntrinsicsRISCV.h" | ||
| #include "llvm/IR/PatternMatch.h" | ||
| #include "llvm/InitializePasses.h" | ||
| #include "llvm/Pass.h" | ||
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| using namespace llvm; | ||
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| #define DEBUG_TYPE "riscv-zacas-abi-fix" | ||
| #define PASS_NAME "RISC-V Zacas ABI fix" | ||
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| namespace { | ||
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| class RISCVZacasABIFix : public FunctionPass, | ||
| public InstVisitor<RISCVZacasABIFix, bool> { | ||
| const RISCVSubtarget *ST; | ||
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| public: | ||
| static char ID; | ||
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| RISCVZacasABIFix() : FunctionPass(ID) {} | ||
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| bool runOnFunction(Function &F) override; | ||
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| StringRef getPassName() const override { return PASS_NAME; } | ||
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| void getAnalysisUsage(AnalysisUsage &AU) const override { | ||
| AU.setPreservesCFG(); | ||
| AU.addRequired<TargetPassConfig>(); | ||
| } | ||
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| bool visitInstruction(Instruction &I) { return false; } | ||
| bool visitAtomicCmpXchgInst(AtomicCmpXchgInst &I); | ||
| }; | ||
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| } // end anonymous namespace | ||
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| // Insert a leading fence (needed for broadest atomics ABI compatibility) | ||
| // only if the Zacas extension is enabled and the AtomicCmpXchgInst has a | ||
| // SequentiallyConsistent failure ordering. | ||
| bool RISCVZacasABIFix::visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) { | ||
| assert(ST->hasStdExtZacas() && "only necessary to run in presence of zacas"); | ||
| IRBuilder<> Builder(&I); | ||
| if (I.getFailureOrdering() != AtomicOrdering::SequentiallyConsistent) | ||
| return false; | ||
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| Builder.CreateFence(AtomicOrdering::SequentiallyConsistent); | ||
| return true; | ||
| } | ||
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| bool RISCVZacasABIFix::runOnFunction(Function &F) { | ||
| auto &TPC = getAnalysis<TargetPassConfig>(); | ||
| auto &TM = TPC.getTM<RISCVTargetMachine>(); | ||
| ST = &TM.getSubtarget<RISCVSubtarget>(F); | ||
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| if (skipFunction(F) || !ST->hasStdExtZacas()) | ||
| return false; | ||
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| bool MadeChange = false; | ||
| for (auto &BB : F) | ||
| for (Instruction &I : llvm::make_early_inc_range(BB)) | ||
| MadeChange |= visit(I); | ||
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| return MadeChange; | ||
| } | ||
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| INITIALIZE_PASS_BEGIN(RISCVZacasABIFix, DEBUG_TYPE, PASS_NAME, false, false) | ||
| INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) | ||
| INITIALIZE_PASS_END(RISCVZacasABIFix, DEBUG_TYPE, PASS_NAME, false, false) | ||
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| char RISCVZacasABIFix::ID = 0; | ||
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| FunctionPass *llvm::createRISCVZacasABIFixPass() { | ||
| return new RISCVZacasABIFix(); | ||
| } |
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