lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp

   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"
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "wasm-reg-numbering"
  32
  33 namespace {
  34 class 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
  46 public:
  47   static char ID; // Pass identification, replacement for typeid
  48   WebAssemblyRegNumbering() : MachineFunctionPass(ID) {}
  49 };
  50 } // end anonymous namespace
  51
  52 char WebAssemblyRegNumbering::ID = 0;
  53 INITIALIZE_PASS(WebAssemblyRegNumbering, DEBUG_TYPE,
  54                 "Assigns WebAssembly register numbers for virtual registers",
  55                 false, false)
  56
  57 FunctionPass *llvm::createWebAssemblyRegNumbering() {
  58   return new WebAssemblyRegNumbering();
  59 }
  60
  61 bool 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 }