166 lines · cpp
1//===-- WebAssemblyPeephole.cpp - WebAssembly Peephole Optimiztions -------===//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-exception6//7//===----------------------------------------------------------------------===//8///9/// \file10/// Late peephole optimizations for WebAssembly.11///12//===----------------------------------------------------------------------===//13 14#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"15#include "WebAssembly.h"16#include "WebAssemblyMachineFunctionInfo.h"17#include "WebAssemblySubtarget.h"18#include "WebAssemblyUtilities.h"19#include "llvm/Analysis/TargetLibraryInfo.h"20#include "llvm/CodeGen/MachineFunctionPass.h"21#include "llvm/CodeGen/MachineInstrBuilder.h"22#include "llvm/CodeGen/MachineRegisterInfo.h"23using namespace llvm;24 25#define DEBUG_TYPE "wasm-peephole"26 27static cl::opt<bool> DisableWebAssemblyFallthroughReturnOpt(28 "disable-wasm-fallthrough-return-opt", cl::Hidden,29 cl::desc("WebAssembly: Disable fallthrough-return optimizations."),30 cl::init(false));31 32namespace {33class WebAssemblyPeephole final : public MachineFunctionPass {34 StringRef getPassName() const override {35 return "WebAssembly late peephole optimizer";36 }37 38 void getAnalysisUsage(AnalysisUsage &AU) const override {39 AU.setPreservesCFG();40 AU.addRequired<TargetLibraryInfoWrapperPass>();41 MachineFunctionPass::getAnalysisUsage(AU);42 }43 44 bool runOnMachineFunction(MachineFunction &MF) override;45 46public:47 static char ID;48 WebAssemblyPeephole() : MachineFunctionPass(ID) {}49};50} // end anonymous namespace51 52char WebAssemblyPeephole::ID = 0;53INITIALIZE_PASS(WebAssemblyPeephole, DEBUG_TYPE,54 "WebAssembly peephole optimizations", false, false)55 56FunctionPass *llvm::createWebAssemblyPeephole() {57 return new WebAssemblyPeephole();58}59 60/// If desirable, rewrite NewReg to a drop register.61static bool maybeRewriteToDrop(unsigned OldReg, unsigned NewReg,62 MachineOperand &MO, WebAssemblyFunctionInfo &MFI,63 MachineRegisterInfo &MRI) {64 bool Changed = false;65 if (OldReg == NewReg) {66 Changed = true;67 Register NewReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));68 MO.setReg(NewReg);69 MO.setIsDead();70 MFI.stackifyVReg(MRI, NewReg);71 }72 return Changed;73}74 75static bool maybeRewriteToFallthrough(MachineInstr &MI, MachineBasicBlock &MBB,76 const MachineFunction &MF,77 WebAssemblyFunctionInfo &MFI,78 MachineRegisterInfo &MRI,79 const WebAssemblyInstrInfo &TII) {80 if (DisableWebAssemblyFallthroughReturnOpt)81 return false;82 if (&MBB != &MF.back())83 return false;84 85 MachineBasicBlock::iterator End = MBB.end();86 --End;87 assert(End->getOpcode() == WebAssembly::END_FUNCTION);88 --End;89 if (&MI != &*End)90 return false;91 92 for (auto &MO : MI.explicit_operands()) {93 // If the operand isn't stackified, insert a COPY to read the operands and94 // stackify them.95 Register Reg = MO.getReg();96 if (!MFI.isVRegStackified(Reg)) {97 unsigned CopyLocalOpc;98 const TargetRegisterClass *RegClass = MRI.getRegClass(Reg);99 CopyLocalOpc = WebAssembly::getCopyOpcodeForRegClass(RegClass);100 Register NewReg = MRI.createVirtualRegister(RegClass);101 BuildMI(MBB, MI, MI.getDebugLoc(), TII.get(CopyLocalOpc), NewReg)102 .addReg(Reg);103 MO.setReg(NewReg);104 MFI.stackifyVReg(MRI, NewReg);105 }106 }107 108 MI.setDesc(TII.get(WebAssembly::FALLTHROUGH_RETURN));109 return true;110}111 112bool WebAssemblyPeephole::runOnMachineFunction(MachineFunction &MF) {113 LLVM_DEBUG({114 dbgs() << "********** Peephole **********\n"115 << "********** Function: " << MF.getName() << '\n';116 });117 118 MachineRegisterInfo &MRI = MF.getRegInfo();119 WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();120 const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();121 const WebAssemblyTargetLowering &TLI =122 *MF.getSubtarget<WebAssemblySubtarget>().getTargetLowering();123 auto &LibInfo =124 getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(MF.getFunction());125 bool Changed = false;126 127 for (auto &MBB : MF)128 for (auto &MI : MBB)129 switch (MI.getOpcode()) {130 default:131 break;132 case WebAssembly::CALL: {133 MachineOperand &Op1 = MI.getOperand(1);134 if (Op1.isSymbol()) {135 StringRef Name(Op1.getSymbolName());136 if (Name == TLI.getLibcallName(RTLIB::MEMCPY) ||137 Name == TLI.getLibcallName(RTLIB::MEMMOVE) ||138 Name == TLI.getLibcallName(RTLIB::MEMSET)) {139 LibFunc Func;140 if (LibInfo.getLibFunc(Name, Func)) {141 const auto &Op2 = MI.getOperand(2);142 if (!Op2.isReg())143 report_fatal_error("Peephole: call to builtin function with "144 "wrong signature, not consuming reg");145 MachineOperand &MO = MI.getOperand(0);146 Register OldReg = MO.getReg();147 Register NewReg = Op2.getReg();148 149 if (MRI.getRegClass(NewReg) != MRI.getRegClass(OldReg))150 report_fatal_error("Peephole: call to builtin function with "151 "wrong signature, from/to mismatch");152 Changed |= maybeRewriteToDrop(OldReg, NewReg, MO, MFI, MRI);153 }154 }155 }156 break;157 }158 // Optimize away an explicit void return at the end of the function.159 case WebAssembly::RETURN:160 Changed |= maybeRewriteToFallthrough(MI, MBB, MF, MFI, MRI, TII);161 break;162 }163 164 return Changed;165}166