WebAssemblyReplacePhysRegs.cpp revision 344779 
1//===-- WebAssemblyReplacePhysRegs.cpp - Replace phys regs with virt regs -===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9///
10/// \file
11/// This file implements a pass that replaces physical registers with
12/// virtual registers.
13///
14/// LLVM expects certain physical registers, such as a stack pointer. However,
15/// WebAssembly doesn't actually have such physical registers. This pass is run
16/// once LLVM no longer needs these registers, and replaces them with virtual
17/// registers, so they can participate in register stackifying and coloring in
18/// the normal way.
19///
20//===----------------------------------------------------------------------===//
21
22#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
23#include "WebAssembly.h"
24#include "WebAssemblyMachineFunctionInfo.h"
25#include "WebAssemblySubtarget.h"
26#include "llvm/CodeGen/MachineFunctionPass.h"
27#include "llvm/CodeGen/MachineRegisterInfo.h"
28#include "llvm/CodeGen/Passes.h"
29#include "llvm/Support/Debug.h"
30#include "llvm/Support/raw_ostream.h"
31using namespace llvm;
32
33#define DEBUG_TYPE "wasm-replace-phys-regs"
34
35namespace {
36class WebAssemblyReplacePhysRegs final : public MachineFunctionPass {
37public:
38  static char ID; // Pass identification, replacement for typeid
39  WebAssemblyReplacePhysRegs() : MachineFunctionPass(ID) {}
40
41private:
42  StringRef getPassName() const override {
43    return "WebAssembly Replace Physical Registers";
44  }
45
46  void getAnalysisUsage(AnalysisUsage &AU) const override {
47    AU.setPreservesCFG();
48    MachineFunctionPass::getAnalysisUsage(AU);
49  }
50
51  bool runOnMachineFunction(MachineFunction &MF) override;
52};
53} // end anonymous namespace
54
55char WebAssemblyReplacePhysRegs::ID = 0;
56INITIALIZE_PASS(WebAssemblyReplacePhysRegs, DEBUG_TYPE,
57                "Replace physical registers with virtual registers", false,
58                false)
59
60FunctionPass *llvm::createWebAssemblyReplacePhysRegs() {
61  return new WebAssemblyReplacePhysRegs();
62}
63
64bool WebAssemblyReplacePhysRegs::runOnMachineFunction(MachineFunction &MF) {
65  LLVM_DEBUG({
66    dbgs() << "********** Replace Physical Registers **********\n"
67           << "********** Function: " << MF.getName() << '\n';
68  });
69
70  MachineRegisterInfo &MRI = MF.getRegInfo();
71  const auto &TRI = *MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
72  bool Changed = false;
73
74  assert(!mustPreserveAnalysisID(LiveIntervalsID) &&
75         "LiveIntervals shouldn't be active yet!");
76  // We don't preserve SSA or liveness.
77  MRI.leaveSSA();
78  MRI.invalidateLiveness();
79
80  for (unsigned PReg = WebAssembly::NoRegister + 1;
81       PReg < WebAssembly::NUM_TARGET_REGS; ++PReg) {
82    // Skip fake registers that are never used explicitly.
83    if (PReg == WebAssembly::VALUE_STACK || PReg == WebAssembly::ARGUMENTS)
84      continue;
85
86    // Replace explicit uses of the physical register with a virtual register.
87    const TargetRegisterClass *RC = TRI.getMinimalPhysRegClass(PReg);
88    unsigned VReg = WebAssembly::NoRegister;
89    for (auto I = MRI.reg_begin(PReg), E = MRI.reg_end(); I != E;) {
90      MachineOperand &MO = *I++;
91      if (!MO.isImplicit()) {
92        if (VReg == WebAssembly::NoRegister)
93          VReg = MRI.createVirtualRegister(RC);
94        MO.setReg(VReg);
95        if (MO.getParent()->isDebugValue())
96          MO.setIsDebug();
97        Changed = true;
98      }
99    }
100  }
101
102  return Changed;
103}
104