1//===- NVPTXProxyRegErasure.cpp - NVPTX Proxy Register Instruction Erasure -==//
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// The pass is needed to remove ProxyReg instructions and restore related
10// registers. The instructions were needed at instruction selection stage to
11// make sure that callseq_end nodes won't be removed as "dead nodes". This can
12// happen when we expand instructions into libcalls and the call site doesn't
13// care about the libcall chain. Call site cares about data flow only, and the
14// latest data flow node happens to be before callseq_end. Therefore the node
15// becomes dangling and "dead". The ProxyReg acts like an additional data flow
16// node *after* the callseq_end in the chain and ensures that everything will be
17// preserved.
18//
19//===----------------------------------------------------------------------===//
20
21#include "NVPTX.h"
22#include "llvm/CodeGen/MachineFunctionPass.h"
23#include "llvm/CodeGen/MachineInstrBuilder.h"
24#include "llvm/CodeGen/MachineRegisterInfo.h"
25#include "llvm/CodeGen/TargetInstrInfo.h"
26#include "llvm/CodeGen/TargetRegisterInfo.h"
27
28using namespace llvm;
29
30namespace llvm {
31void initializeNVPTXProxyRegErasurePass(PassRegistry &);
32}
33
34namespace {
35
36struct NVPTXProxyRegErasure : public MachineFunctionPass {
37public:
38  static char ID;
39  NVPTXProxyRegErasure() : MachineFunctionPass(ID) {
40    initializeNVPTXProxyRegErasurePass(*PassRegistry::getPassRegistry());
41  }
42
43  bool runOnMachineFunction(MachineFunction &MF) override;
44
45  StringRef getPassName() const override {
46    return "NVPTX Proxy Register Instruction Erasure";
47  }
48
49  void getAnalysisUsage(AnalysisUsage &AU) const override {
50    MachineFunctionPass::getAnalysisUsage(AU);
51  }
52
53private:
54  void replaceMachineInstructionUsage(MachineFunction &MF, MachineInstr &MI);
55
56  void replaceRegisterUsage(MachineInstr &Instr, MachineOperand &From,
57                            MachineOperand &To);
58};
59
60} // namespace
61
62char NVPTXProxyRegErasure::ID = 0;
63
64INITIALIZE_PASS(NVPTXProxyRegErasure, "nvptx-proxyreg-erasure", "NVPTX ProxyReg Erasure", false, false)
65
66bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {
67  SmallVector<MachineInstr *, 16> RemoveList;
68
69  for (auto &BB : MF) {
70    for (auto &MI : BB) {
71      switch (MI.getOpcode()) {
72      case NVPTX::ProxyRegI1:
73      case NVPTX::ProxyRegI16:
74      case NVPTX::ProxyRegI32:
75      case NVPTX::ProxyRegI64:
76      case NVPTX::ProxyRegF32:
77      case NVPTX::ProxyRegF64:
78        replaceMachineInstructionUsage(MF, MI);
79        RemoveList.push_back(&MI);
80        break;
81      }
82    }
83  }
84
85  for (auto *MI : RemoveList) {
86    MI->eraseFromParent();
87  }
88
89  return !RemoveList.empty();
90}
91
92void NVPTXProxyRegErasure::replaceMachineInstructionUsage(MachineFunction &MF,
93                                                          MachineInstr &MI) {
94  auto &InOp = *MI.uses().begin();
95  auto &OutOp = *MI.defs().begin();
96
97  assert(InOp.isReg() && "ProxyReg input operand should be a register.");
98  assert(OutOp.isReg() && "ProxyReg output operand should be a register.");
99
100  for (auto &BB : MF) {
101    for (auto &I : BB) {
102      replaceRegisterUsage(I, OutOp, InOp);
103    }
104  }
105}
106
107void NVPTXProxyRegErasure::replaceRegisterUsage(MachineInstr &Instr,
108                                                MachineOperand &From,
109                                                MachineOperand &To) {
110  for (auto &Op : Instr.uses()) {
111    if (Op.isReg() && Op.getReg() == From.getReg()) {
112      Op.setReg(To.getReg());
113    }
114  }
115}
116
117MachineFunctionPass *llvm::createNVPTXProxyRegErasurePass() {
118  return new NVPTXProxyRegErasure();
119}
120