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(Reg: PReg);
84 unsigned VReg = WebAssembly::NoRegister;
85 for (MachineOperand &MO :
86 llvm::make_early_inc_range(Range: MRI.reg_operands(Reg: PReg))) {
87 if (!MO.isImplicit()) {
88 if (VReg == WebAssembly::NoRegister) {
89 VReg = MRI.createVirtualRegister(RegClass: 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(VReg).virtRegIndex() << ")\n";
97 });
98 }
99 }
100 MO.setReg(VReg);
101 Changed = true;
102 }
103 }
104 }
105
106 return Changed;
107}
108