1//===----- RISCVZacasABIFix.cpp -------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass implements a fence insertion for an atomic cmpxchg in a case that
10// isn't easy to do with the current AtomicExpandPass hooks API.
11//
12//===----------------------------------------------------------------------===//
13
14#include "RISCV.h"
15#include "RISCVTargetMachine.h"
16#include "llvm/ADT/Statistic.h"
17#include "llvm/Analysis/ValueTracking.h"
18#include "llvm/CodeGen/TargetPassConfig.h"
19#include "llvm/IR/Dominators.h"
20#include "llvm/IR/IRBuilder.h"
21#include "llvm/IR/InstVisitor.h"
22#include "llvm/IR/Intrinsics.h"
23#include "llvm/InitializePasses.h"
24#include "llvm/Pass.h"
25
26using namespace llvm;
27
28#define DEBUG_TYPE "riscv-zacas-abi-fix"
29#define PASS_NAME "RISC-V Zacas ABI fix"
30
31namespace {
32
33class RISCVZacasABIFix : public FunctionPass,
34 public InstVisitor<RISCVZacasABIFix, bool> {
35 const RISCVSubtarget *ST;
36
37public:
38 static char ID;
39
40 RISCVZacasABIFix() : FunctionPass(ID) {}
41
42 bool runOnFunction(Function &F) override;
43
44 StringRef getPassName() const override { return PASS_NAME; }
45
46 void getAnalysisUsage(AnalysisUsage &AU) const override {
47 AU.setPreservesCFG();
48 AU.addRequired<TargetPassConfig>();
49 }
50
51 bool visitInstruction(Instruction &I) { return false; }
52 bool visitAtomicCmpXchgInst(AtomicCmpXchgInst &I);
53};
54
55} // end anonymous namespace
56
57// Insert a leading fence (needed for broadest atomics ABI compatibility)
58// only if the Zacas extension is enabled and the AtomicCmpXchgInst has a
59// SequentiallyConsistent failure ordering.
60bool RISCVZacasABIFix::visitAtomicCmpXchgInst(AtomicCmpXchgInst &I) {
61 assert(ST->hasStdExtZacas() && "only necessary to run in presence of zacas");
62 IRBuilder<> Builder(&I);
63 if (I.getFailureOrdering() != AtomicOrdering::SequentiallyConsistent)
64 return false;
65
66 Builder.CreateFence(Ordering: AtomicOrdering::SequentiallyConsistent);
67 return true;
68}
69
70bool RISCVZacasABIFix::runOnFunction(Function &F) {
71 auto &TPC = getAnalysis<TargetPassConfig>();
72 auto &TM = TPC.getTM<RISCVTargetMachine>();
73 ST = &TM.getSubtarget<RISCVSubtarget>(F);
74
75 if (skipFunction(F) || !ST->hasStdExtZacas())
76 return false;
77
78 bool MadeChange = false;
79 for (auto &BB : F)
80 for (Instruction &I : llvm::make_early_inc_range(Range&: BB))
81 MadeChange |= visit(I);
82
83 return MadeChange;
84}
85
86INITIALIZE_PASS_BEGIN(RISCVZacasABIFix, DEBUG_TYPE, PASS_NAME, false, false)
87INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
88INITIALIZE_PASS_END(RISCVZacasABIFix, DEBUG_TYPE, PASS_NAME, false, false)
89
90char RISCVZacasABIFix::ID = 0;
91
92FunctionPass *llvm::createRISCVZacasABIFixPass() {
93 return new RISCVZacasABIFix();
94}
95