WebAssemblyRegNumbering.cpp revision 341825 
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/// This file implements a pass which assigns WebAssembly register
12/// numbers for CodeGen virtual registers.
13///
14//===----------------------------------------------------------------------===//
15
16#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
17#include "WebAssembly.h"
18#include "WebAssemblyMachineFunctionInfo.h"
19#include "WebAssemblySubtarget.h"
20#include "WebAssemblyUtilities.h"
21#include "llvm/ADT/SCCIterator.h"
22#include "llvm/CodeGen/MachineFrameInfo.h"
23#include "llvm/CodeGen/MachineFunction.h"
24#include "llvm/CodeGen/MachineInstrBuilder.h"
25#include "llvm/CodeGen/MachineLoopInfo.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-reg-numbering"
33
34namespace {
35class WebAssemblyRegNumbering final : public MachineFunctionPass {
36  StringRef getPassName() const override {
37    return "WebAssembly Register Numbering";
38  }
39
40  void getAnalysisUsage(AnalysisUsage &AU) const override {
41    AU.setPreservesCFG();
42    MachineFunctionPass::getAnalysisUsage(AU);
43  }
44
45  bool runOnMachineFunction(MachineFunction &MF) override;
46
47public:
48  static char ID; // Pass identification, replacement for typeid
49  WebAssemblyRegNumbering() : MachineFunctionPass(ID) {}
50};
51} // end anonymous namespace
52
53char WebAssemblyRegNumbering::ID = 0;
54INITIALIZE_PASS(WebAssemblyRegNumbering, DEBUG_TYPE,
55                "Assigns WebAssembly register numbers for virtual registers",
56                false, false)
57
58FunctionPass *llvm::createWebAssemblyRegNumbering() {
59  return new WebAssemblyRegNumbering();
60}
61
62bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
63  LLVM_DEBUG(dbgs() << "********** Register Numbering **********\n"
64                       "********** Function: "
65                    << MF.getName() << '\n');
66
67  WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
68  MachineRegisterInfo &MRI = MF.getRegInfo();
69
70  MFI.initWARegs();
71
72  // WebAssembly argument registers are in the same index space as local
73  // variables. Assign the numbers for them first.
74  MachineBasicBlock &EntryMBB = MF.front();
75  for (MachineInstr &MI : EntryMBB) {
76    if (!WebAssembly::isArgument(MI))
77      break;
78
79    int64_t Imm = MI.getOperand(1).getImm();
80    LLVM_DEBUG(dbgs() << "Arg VReg " << MI.getOperand(0).getReg()
81                      << " -> WAReg " << Imm << "\n");
82    MFI.setWAReg(MI.getOperand(0).getReg(), Imm);
83  }
84
85  // Then assign regular WebAssembly registers for all remaining used
86  // virtual registers. TODO: Consider sorting the registers by frequency of
87  // use, to maximize usage of small immediate fields.
88  unsigned NumVRegs = MF.getRegInfo().getNumVirtRegs();
89  unsigned NumStackRegs = 0;
90  // Start the numbering for locals after the arg regs
91  unsigned CurReg = MFI.getParams().size();
92  for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {
93    unsigned VReg = TargetRegisterInfo::index2VirtReg(VRegIdx);
94    // Skip unused registers.
95    if (MRI.use_empty(VReg))
96      continue;
97    // Handle stackified registers.
98    if (MFI.isVRegStackified(VReg)) {
99      LLVM_DEBUG(dbgs() << "VReg " << VReg << " -> WAReg "
100                        << (INT32_MIN | NumStackRegs) << "\n");
101      MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);
102      continue;
103    }
104    if (MFI.getWAReg(VReg) == WebAssemblyFunctionInfo::UnusedReg) {
105      LLVM_DEBUG(dbgs() << "VReg " << VReg << " -> WAReg " << CurReg << "\n");
106      MFI.setWAReg(VReg, CurReg++);
107    }
108  }
109
110  return true;
111}
112