WebAssemblyRegNumbering.cpp revision 292915 
1//===-- WebAssemblyRegNumbering.cpp - Register Numbering ------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9///
10/// \file
11/// \brief This file implements a pass which assigns WebAssembly register
12/// numbers for CodeGen virtual registers.
13///
14//===----------------------------------------------------------------------===//
15
16#include "WebAssembly.h"
17#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
18#include "WebAssemblyMachineFunctionInfo.h"
19#include "WebAssemblySubtarget.h"
20#include "llvm/ADT/SCCIterator.h"
21#include "llvm/CodeGen/MachineFunction.h"
22#include "llvm/CodeGen/MachineFrameInfo.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  const char *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;
53FunctionPass *llvm::createWebAssemblyRegNumbering() {
54  return new WebAssemblyRegNumbering();
55}
56
57bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
58  DEBUG(dbgs() << "********** Register Numbering **********\n"
59                  "********** Function: "
60               << MF.getName() << '\n');
61
62  WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
63  MachineRegisterInfo &MRI = MF.getRegInfo();
64  const MachineFrameInfo &FrameInfo = *MF.getFrameInfo();
65
66  MFI.initWARegs();
67
68  // WebAssembly argument registers are in the same index space as local
69  // variables. Assign the numbers for them first.
70  MachineBasicBlock &EntryMBB = MF.front();
71  for (MachineInstr &MI : EntryMBB) {
72    switch (MI.getOpcode()) {
73    case WebAssembly::ARGUMENT_I32:
74    case WebAssembly::ARGUMENT_I64:
75    case WebAssembly::ARGUMENT_F32:
76    case WebAssembly::ARGUMENT_F64:
77      MFI.setWAReg(MI.getOperand(0).getReg(), MI.getOperand(1).getImm());
78      break;
79    default:
80      break;
81    }
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 NumArgRegs = MFI.getParams().size();
88  unsigned NumVRegs = MF.getRegInfo().getNumVirtRegs();
89  unsigned NumStackRegs = 0;
90  unsigned CurReg = 0;
91  for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {
92    unsigned VReg = TargetRegisterInfo::index2VirtReg(VRegIdx);
93    // Handle stackified registers.
94    if (MFI.isVRegStackified(VReg)) {
95      MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);
96      continue;
97    }
98    // Skip unused registers.
99    if (MRI.use_empty(VReg))
100      continue;
101    if (MFI.getWAReg(VReg) == WebAssemblyFunctionInfo::UnusedReg)
102      MFI.setWAReg(VReg, NumArgRegs + CurReg++);
103  }
104  // Allocate locals for used physical registers
105  if (FrameInfo.getStackSize() > 0)
106    MFI.addPReg(WebAssembly::SP32, CurReg++);
107
108  return true;
109}
110