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"
30using namespace llvm;
31
32#define DEBUG_TYPE "wasm-replace-phys-regs"
33
34namespace {
35class WebAssemblyReplacePhysRegs final : public MachineFunctionPass {
36public:
37  static char ID; // Pass identification, replacement for typeid
38  WebAssemblyReplacePhysRegs() : MachineFunctionPass(ID) {}
39
40private:
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
54char WebAssemblyReplacePhysRegs::ID = 0;
55INITIALIZE_PASS(WebAssemblyReplacePhysRegs, DEBUG_TYPE,
56                "Replace physical registers with virtual registers", false,
57                false)
58
59FunctionPass *llvm::createWebAssemblyReplacePhysRegs() {
60  return new WebAssemblyReplacePhysRegs();
61}
62
63bool 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  auto &TRI = *MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
71  bool Changed = false;
72
73  assert(!mustPreserveAnalysisID(LiveIntervalsID) &&
74         "LiveIntervals shouldn't be active yet!");
75
76  for (unsigned PReg = WebAssembly::NoRegister + 1;
77       PReg < WebAssembly::NUM_TARGET_REGS; ++PReg) {
78    // Skip fake registers that are never used explicitly.
79    if (PReg == WebAssembly::VALUE_STACK || PReg == WebAssembly::ARGUMENTS)
80      continue;
81
82    // Replace explicit uses of the physical register with a virtual register.
83    const TargetRegisterClass *RC = TRI.getMinimalPhysRegClass(PReg);
84    unsigned VReg = WebAssembly::NoRegister;
85    for (MachineOperand &MO :
86         llvm::make_early_inc_range(MRI.reg_operands(PReg))) {
87      if (!MO.isImplicit()) {
88        if (VReg == WebAssembly::NoRegister) {
89          VReg = MRI.createVirtualRegister(RC);
90          if (PReg == TRI.getFrameRegister(MF)) {
91            auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
92            assert(!FI->isFrameBaseVirtual());
93            FI->setFrameBaseVreg(VReg);
94            LLVM_DEBUG({
95              dbgs() << "replacing preg " << PReg << " with " << VReg << " ("
96                     << Register::virtReg2Index(VReg) << ")\n";
97            });
98          }
99        }
100        MO.setReg(VReg);
101        Changed = true;
102      }
103    }
104  }
105
106  return Changed;
107}
108