1//===-- WebAssemblyRegNumbering.cpp - Register Numbering ------------------===//
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 which assigns WebAssembly register
11/// numbers for CodeGen virtual registers.
12///
13//===----------------------------------------------------------------------===//
14
15#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
16#include "WebAssembly.h"
17#include "WebAssemblyMachineFunctionInfo.h"
18#include "WebAssemblySubtarget.h"
19#include "WebAssemblyUtilities.h"
20#include "llvm/ADT/SCCIterator.h"
21#include "llvm/CodeGen/MachineFrameInfo.h"
22#include "llvm/CodeGen/MachineFunction.h"
23#include "llvm/CodeGen/MachineInstrBuilder.h"
24#include "llvm/CodeGen/MachineLoopInfo.h"
25#include "llvm/CodeGen/MachineRegisterInfo.h"
26#include "llvm/CodeGen/Passes.h"
27#include "llvm/Support/Debug.h"
28#include "llvm/Support/raw_ostream.h"
29using namespace llvm;
30
31#define DEBUG_TYPE "wasm-reg-numbering"
32
33namespace {
34class WebAssemblyRegNumbering final : public MachineFunctionPass {
35  StringRef getPassName() const override {
36    return "WebAssembly Register Numbering";
37  }
38
39  void getAnalysisUsage(AnalysisUsage &AU) const override {
40    AU.setPreservesCFG();
41    MachineFunctionPass::getAnalysisUsage(AU);
42  }
43
44  bool runOnMachineFunction(MachineFunction &MF) override;
45
46public:
47  static char ID; // Pass identification, replacement for typeid
48  WebAssemblyRegNumbering() : MachineFunctionPass(ID) {}
49};
50} // end anonymous namespace
51
52char WebAssemblyRegNumbering::ID = 0;
53INITIALIZE_PASS(WebAssemblyRegNumbering, DEBUG_TYPE,
54                "Assigns WebAssembly register numbers for virtual registers",
55                false, false)
56
57FunctionPass *llvm::createWebAssemblyRegNumbering() {
58  return new WebAssemblyRegNumbering();
59}
60
61bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
62  LLVM_DEBUG(dbgs() << "********** Register Numbering **********\n"
63                       "********** Function: "
64                    << MF.getName() << '\n');
65
66  WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
67  MachineRegisterInfo &MRI = MF.getRegInfo();
68
69  MFI.initWARegs();
70
71  // WebAssembly argument registers are in the same index space as local
72  // variables. Assign the numbers for them first.
73  MachineBasicBlock &EntryMBB = MF.front();
74  for (MachineInstr &MI : EntryMBB) {
75    if (!WebAssembly::isArgument(MI.getOpcode()))
76      break;
77
78    int64_t Imm = MI.getOperand(1).getImm();
79    LLVM_DEBUG(dbgs() << "Arg VReg " << MI.getOperand(0).getReg()
80                      << " -> WAReg " << Imm << "\n");
81    MFI.setWAReg(MI.getOperand(0).getReg(), Imm);
82  }
83
84  // Then assign regular WebAssembly registers for all remaining used
85  // virtual registers. TODO: Consider sorting the registers by frequency of
86  // use, to maximize usage of small immediate fields.
87  unsigned NumVRegs = MF.getRegInfo().getNumVirtRegs();
88  unsigned NumStackRegs = 0;
89  // Start the numbering for locals after the arg regs
90  unsigned CurReg = MFI.getParams().size();
91  for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {
92    unsigned VReg = Register::index2VirtReg(VRegIdx);
93    // Skip unused registers.
94    if (MRI.use_empty(VReg))
95      continue;
96    // Handle stackified registers.
97    if (MFI.isVRegStackified(VReg)) {
98      LLVM_DEBUG(dbgs() << "VReg " << VReg << " -> WAReg "
99                        << (INT32_MIN | NumStackRegs) << "\n");
100      MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);
101      continue;
102    }
103    if (MFI.getWAReg(VReg) == WebAssemblyFunctionInfo::UnusedReg) {
104      LLVM_DEBUG(dbgs() << "VReg " << VReg << " -> WAReg " << CurReg << "\n");
105      MFI.setWAReg(VReg, CurReg++);
106    }
107  }
108
109  return true;
110}
111