lib/Target/WebAssembly/WebAssemblyReplacePhysRegs.cpp

   1 //===-- WebAssemblyReplacePhysRegs.cpp - Replace phys regs with virt regs -===//
   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 /// This file implements a pass that replaces physical registers with
  11 /// virtual registers.
  12 ///
  13 /// LLVM expects certain physical registers, such as a stack pointer. However,
  14 /// WebAssembly doesn't actually have such physical registers. This pass is run
  15 /// once LLVM no longer needs these registers, and replaces them with virtual
  16 /// registers, so they can participate in register stackifying and coloring in
  17 /// the normal way.
  18 ///
  19 //===----------------------------------------------------------------------===//
  20
  21 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
  22 #include "WebAssembly.h"
  23 #include "WebAssemblyMachineFunctionInfo.h"
  24 #include "WebAssemblySubtarget.h"
  25 #include "llvm/CodeGen/MachineFunctionPass.h"
  26 #include "llvm/CodeGen/MachineRegisterInfo.h"
  27 #include "llvm/CodeGen/Passes.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/raw_ostream.h"
  30 using namespace llvm;
  31
  32 #define DEBUG_TYPE "wasm-replace-phys-regs"
  33
  34 namespace {
  35 class WebAssemblyReplacePhysRegs final : public MachineFunctionPass {
  36 public:
  37   static char ID; // Pass identification, replacement for typeid
  38   WebAssemblyReplacePhysRegs() : MachineFunctionPass(ID) {}
  39
  40 private:
  41   StringRef getPassName() const override {
  42     return "WebAssembly Replace Physical Registers";
  43   }
  44
  45   void getAnalysisUsage(AnalysisUsage &AU) const override {
  46     AU.setPreservesCFG();
  47     MachineFunctionPass::getAnalysisUsage(AU);
  48   }
  49
  50   bool runOnMachineFunction(MachineFunction &MF) override;
  51 };
  52 } // end anonymous namespace
  53
  54 char WebAssemblyReplacePhysRegs::ID = 0;
  55 INITIALIZE_PASS(WebAssemblyReplacePhysRegs, DEBUG_TYPE,
  56                 "Replace physical registers with virtual registers", false,
  57                 false)
  58
  59 FunctionPass *llvm::createWebAssemblyReplacePhysRegs() {
  60   return new WebAssemblyReplacePhysRegs();
  61 }
  62
  63 bool WebAssemblyReplacePhysRegs::runOnMachineFunction(MachineFunction &MF) {
  64   LLVM_DEBUG({
  65     dbgs() << "********** Replace Physical Registers **********\n"
  66            << "********** Function: " << MF.getName() << '\n';
  67   });
  68
  69   MachineRegisterInfo &MRI = MF.getRegInfo();
  70   const auto &TRI = *MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
  71   bool Changed = false;
  72
  73   assert(!mustPreserveAnalysisID(LiveIntervalsID) &&
  74          "LiveIntervals shouldn't be active yet!");
  75   // We don't preserve SSA or liveness.
  76   MRI.leaveSSA();
  77   MRI.invalidateLiveness();
  78
  79   for (unsigned PReg = WebAssembly::NoRegister + 1;
  80        PReg < WebAssembly::NUM_TARGET_REGS; ++PReg) {
  81     // Skip fake registers that are never used explicitly.
  82     if (PReg == WebAssembly::VALUE_STACK || PReg == WebAssembly::ARGUMENTS)
  83       continue;
  84
  85     // Replace explicit uses of the physical register with a virtual register.
  86     const TargetRegisterClass *RC = TRI.getMinimalPhysRegClass(PReg);
  87     unsigned VReg = WebAssembly::NoRegister;
  88     for (auto I = MRI.reg_begin(PReg), E = MRI.reg_end(); I != E;) {
  89       MachineOperand &MO = *I++;
  90       if (!MO.isImplicit()) {
  91         if (VReg == WebAssembly::NoRegister)
  92           VReg = MRI.createVirtualRegister(RC);
  93         MO.setReg(VReg);
  94         if (MO.getParent()->isDebugValue())
  95           MO.setIsDebug();
  96         Changed = true;
  97       }
  98     }
  99   }
 100
 101   return Changed;
 102 }