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 "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"
30 using namespace llvm;
31 
32 #define DEBUG_TYPE "wasm-reg-numbering"
33 
34 namespace {
35 class 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 
47 public:
48   static char ID; // Pass identification, replacement for typeid
49   WebAssemblyRegNumbering() : MachineFunctionPass(ID) {}
50 };
51 } // end anonymous namespace
52 
53 char WebAssemblyRegNumbering::ID = 0;
54 FunctionPass *llvm::createWebAssemblyRegNumbering() {
55   return new WebAssemblyRegNumbering();
56 }
57 
58 bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
59   DEBUG(dbgs() << "********** Register Numbering **********\n"
60                   "********** Function: "
61                << MF.getName() << '\n');
62 
63   WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
64   MachineRegisterInfo &MRI = MF.getRegInfo();
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     if (!WebAssembly::isArgument(MI))
73       break;
74 
75     int64_t Imm = MI.getOperand(1).getImm();
76     DEBUG(dbgs() << "Arg VReg " << MI.getOperand(0).getReg() << " -> WAReg "
77                  << Imm << "\n");
78     MFI.setWAReg(MI.getOperand(0).getReg(), Imm);
79   }
80 
81   // Then assign regular WebAssembly registers for all remaining used
82   // virtual registers. TODO: Consider sorting the registers by frequency of
83   // use, to maximize usage of small immediate fields.
84   unsigned NumVRegs = MF.getRegInfo().getNumVirtRegs();
85   unsigned NumStackRegs = 0;
86   // Start the numbering for locals after the arg regs
87   unsigned CurReg = MFI.getParams().size();
88   for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {
89     unsigned VReg = TargetRegisterInfo::index2VirtReg(VRegIdx);
90     // Skip unused registers.
91     if (MRI.use_empty(VReg))
92       continue;
93     // Handle stackified registers.
94     if (MFI.isVRegStackified(VReg)) {
95       DEBUG(dbgs() << "VReg " << VReg << " -> WAReg "
96                    << (INT32_MIN | NumStackRegs) << "\n");
97       MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);
98       continue;
99     }
100     if (MFI.getWAReg(VReg) == WebAssemblyFunctionInfo::UnusedReg) {
101       DEBUG(dbgs() << "VReg " << VReg << " -> WAReg " << CurReg << "\n");
102       MFI.setWAReg(VReg, CurReg++);
103     }
104   }
105 
106   return true;
107 }
108