xref: /freebsd/contrib/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyReplacePhysRegs.cpp (revision f976241773df2260e6170317080761d1c5814fe5)
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 }
103