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/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   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 
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 FunctionPass *llvm::createWebAssemblyRegNumbering() {
54   return new WebAssemblyRegNumbering();
55 }
56 
57 bool 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       DEBUG(dbgs() << "Arg VReg " << MI.getOperand(0).getReg() << " -> WAReg "
78                    << MI.getOperand(1).getImm() << "\n");
79       MFI.setWAReg(MI.getOperand(0).getReg(), MI.getOperand(1).getImm());
80       break;
81     default:
82       break;
83     }
84   }
85 
86   // Then assign regular WebAssembly registers for all remaining used
87   // virtual registers. TODO: Consider sorting the registers by frequency of
88   // use, to maximize usage of small immediate fields.
89   unsigned NumVRegs = MF.getRegInfo().getNumVirtRegs();
90   unsigned NumStackRegs = 0;
91   // Start the numbering for locals after the arg regs
92   unsigned CurReg = MFI.getParams().size();
93   for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {
94     unsigned VReg = TargetRegisterInfo::index2VirtReg(VRegIdx);
95     // Skip unused registers.
96     if (MRI.use_empty(VReg))
97       continue;
98     // Handle stackified registers.
99     if (MFI.isVRegStackified(VReg)) {
100       DEBUG(dbgs() << "VReg " << VReg << " -> WAReg "
101                    << (INT32_MIN | NumStackRegs) << "\n");
102       MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);
103       continue;
104     }
105     if (MFI.getWAReg(VReg) == WebAssemblyFunctionInfo::UnusedReg) {
106       DEBUG(dbgs() << "VReg " << VReg << " -> WAReg " << CurReg << "\n");
107       MFI.setWAReg(VReg, CurReg++);
108     }
109   }
110   // Allocate locals for used physical registers
111   bool HasFP = MF.getSubtarget().getFrameLowering()->hasFP(MF);
112   if (FrameInfo.getStackSize() > 0 || FrameInfo.adjustsStack() || HasFP) {
113     DEBUG(dbgs() << "PReg SP " << CurReg << "\n");
114     MFI.addPReg(WebAssembly::SP32, CurReg++);
115   }
116   if (HasFP) {
117     DEBUG(dbgs() << "PReg FP " << CurReg << "\n");
118     MFI.addPReg(WebAssembly::FP32, CurReg++);
119   }
120 
121   return true;
122 }
123