lib/Target/WebAssembly/WebAssemblyPeephole.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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 ///
   9 /// \file
  10 /// 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 "llvm/Analysis/TargetLibraryInfo.h"
  19 #include "llvm/CodeGen/MachineFunctionPass.h"
  20 #include "llvm/CodeGen/MachineInstrBuilder.h"
  21 #include "llvm/CodeGen/MachineRegisterInfo.h"
  22 using namespace llvm;
  23
  24 #define DEBUG_TYPE "wasm-peephole"
  25
  26 static cl::opt<bool> DisableWebAssemblyFallthroughReturnOpt(
  27     "disable-wasm-fallthrough-return-opt", cl::Hidden,
  28     cl::desc("WebAssembly: Disable fallthrough-return optimizations."),
  29     cl::init(false));
  30
  31 namespace {
  32 class WebAssemblyPeephole final : public MachineFunctionPass {
  33   StringRef getPassName() const override {
  34     return "WebAssembly late peephole optimizer";
  35   }
  36
  37   void getAnalysisUsage(AnalysisUsage &AU) const override {
  38     AU.setPreservesCFG();
  39     AU.addRequired<TargetLibraryInfoWrapperPass>();
  40     MachineFunctionPass::getAnalysisUsage(AU);
  41   }
  42
  43   bool runOnMachineFunction(MachineFunction &MF) override;
  44
  45 public:
  46   static char ID;
  47   WebAssemblyPeephole() : MachineFunctionPass(ID) {}
  48 };
  49 } // end anonymous namespace
  50
  51 char WebAssemblyPeephole::ID = 0;
  52 INITIALIZE_PASS(WebAssemblyPeephole, DEBUG_TYPE,
  53                 "WebAssembly peephole optimizations", false, false)
  54
  55 FunctionPass *llvm::createWebAssemblyPeephole() {
  56   return new WebAssemblyPeephole();
  57 }
  58
  59 /// If desirable, rewrite NewReg to a drop register.
  60 static bool maybeRewriteToDrop(unsigned OldReg, unsigned NewReg,
  61                                MachineOperand &MO, WebAssemblyFunctionInfo &MFI,
  62                                MachineRegisterInfo &MRI) {
  63   bool Changed = false;
  64   if (OldReg == NewReg) {
  65     Changed = true;
  66     Register NewReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));
  67     MO.setReg(NewReg);
  68     MO.setIsDead();
  69     MFI.stackifyVReg(NewReg);
  70   }
  71   return Changed;
  72 }
  73
  74 static bool maybeRewriteToFallthrough(MachineInstr &MI, MachineBasicBlock &MBB,
  75                                       const MachineFunction &MF,
  76                                       WebAssemblyFunctionInfo &MFI,
  77                                       MachineRegisterInfo &MRI,
  78                                       const WebAssemblyInstrInfo &TII) {
  79   if (DisableWebAssemblyFallthroughReturnOpt)
  80     return false;
  81   if (&MBB != &MF.back())
  82     return false;
  83
  84   MachineBasicBlock::iterator End = MBB.end();
  85   --End;
  86   assert(End->getOpcode() == WebAssembly::END_FUNCTION);
  87   --End;
  88   if (&MI != &*End)
  89     return false;
  90
  91   for (auto &MO : MI.explicit_operands()) {
  92     // If the operand isn't stackified, insert a COPY to read the operands and
  93     // stackify them.
  94     Register Reg = MO.getReg();
  95     if (!MFI.isVRegStackified(Reg)) {
  96       unsigned CopyLocalOpc;
  97       const TargetRegisterClass *RegClass = MRI.getRegClass(Reg);
  98       switch (RegClass->getID()) {
  99       case WebAssembly::I32RegClassID:
 100         CopyLocalOpc = WebAssembly::COPY_I32;
 101         break;
 102       case WebAssembly::I64RegClassID:
 103         CopyLocalOpc = WebAssembly::COPY_I64;
 104         break;
 105       case WebAssembly::F32RegClassID:
 106         CopyLocalOpc = WebAssembly::COPY_F32;
 107         break;
 108       case WebAssembly::F64RegClassID:
 109         CopyLocalOpc = WebAssembly::COPY_F64;
 110         break;
 111       case WebAssembly::V128RegClassID:
 112         CopyLocalOpc = WebAssembly::COPY_V128;
 113         break;
 114       case WebAssembly::EXNREFRegClassID:
 115         CopyLocalOpc = WebAssembly::COPY_EXNREF;
 116         break;
 117       default:
 118         llvm_unreachable("Unexpected register class for return operand");
 119       }
 120       Register NewReg = MRI.createVirtualRegister(RegClass);
 121       BuildMI(MBB, MI, MI.getDebugLoc(), TII.get(CopyLocalOpc), NewReg)
 122           .addReg(Reg);
 123       MO.setReg(NewReg);
 124       MFI.stackifyVReg(NewReg);
 125     }
 126   }
 127
 128   MI.setDesc(TII.get(WebAssembly::FALLTHROUGH_RETURN));
 129   return true;
 130 }
 131
 132 bool WebAssemblyPeephole::runOnMachineFunction(MachineFunction &MF) {
 133   LLVM_DEBUG({
 134     dbgs() << "********** Peephole **********\n"
 135            << "********** Function: " << MF.getName() << '\n';
 136   });
 137
 138   MachineRegisterInfo &MRI = MF.getRegInfo();
 139   WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
 140   const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
 141   const WebAssemblyTargetLowering &TLI =
 142       *MF.getSubtarget<WebAssemblySubtarget>().getTargetLowering();
 143   auto &LibInfo =
 144       getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(MF.getFunction());
 145   bool Changed = false;
 146
 147   for (auto &MBB : MF)
 148     for (auto &MI : MBB)
 149       switch (MI.getOpcode()) {
 150       default:
 151         break;
 152       case WebAssembly::CALL_i32:
 153       case WebAssembly::CALL_i64: {
 154         MachineOperand &Op1 = MI.getOperand(1);
 155         if (Op1.isSymbol()) {
 156           StringRef Name(Op1.getSymbolName());
 157           if (Name == TLI.getLibcallName(RTLIB::MEMCPY) ||
 158               Name == TLI.getLibcallName(RTLIB::MEMMOVE) ||
 159               Name == TLI.getLibcallName(RTLIB::MEMSET)) {
 160             LibFunc Func;
 161             if (LibInfo.getLibFunc(Name, Func)) {
 162               const auto &Op2 = MI.getOperand(2);
 163               if (!Op2.isReg())
 164                 report_fatal_error("Peephole: call to builtin function with "
 165                                    "wrong signature, not consuming reg");
 166               MachineOperand &MO = MI.getOperand(0);
 167               Register OldReg = MO.getReg();
 168               Register NewReg = Op2.getReg();
 169
 170               if (MRI.getRegClass(NewReg) != MRI.getRegClass(OldReg))
 171                 report_fatal_error("Peephole: call to builtin function with "
 172                                    "wrong signature, from/to mismatch");
 173               Changed |= maybeRewriteToDrop(OldReg, NewReg, MO, MFI, MRI);
 174             }
 175           }
 176         }
 177         break;
 178       }
 179       // Optimize away an explicit void return at the end of the function.
 180       case WebAssembly::RETURN:
 181         Changed |= maybeRewriteToFallthrough(MI, MBB, MF, MFI, MRI, TII);
 182         break;
 183       }
 184
 185   return Changed;
 186 }