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
WebAssemblyReplacePhysRegs()38 WebAssemblyReplacePhysRegs() : MachineFunctionPass(ID) {}
39
40 private:
getPassName() const41 StringRef getPassName() const override {
42 return "WebAssembly Replace Physical Registers";
43 }
44
getAnalysisUsage(AnalysisUsage & AU) const45 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
createWebAssemblyReplacePhysRegs()59 FunctionPass *llvm::createWebAssemblyReplacePhysRegs() {
60 return new WebAssemblyReplacePhysRegs();
61 }
62
runOnMachineFunction(MachineFunction & MF)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 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 if (PReg == TRI.getFrameRegister(MF)) {
94 auto FI = MF.getInfo<WebAssemblyFunctionInfo>();
95 assert(!FI->isFrameBaseVirtual());
96 FI->setFrameBaseVreg(VReg);
97 LLVM_DEBUG({
98 dbgs() << "replacing preg " << PReg << " with " << VReg << " ("
99 << Register::virtReg2Index(VReg) << ")\n";
100 });
101 }
102 }
103 MO.setReg(VReg);
104 if (MO.getParent()->isDebugValue())
105 MO.setIsDebug();
106 Changed = true;
107 }
108 }
109 }
110
111 return Changed;
112 }
113