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/MachineRegisterInfo.h"
24#include "llvm/CodeGen/TargetRegisterInfo.h"
25
26using namespace llvm;
27
28namespace {
29
30struct NVPTXProxyRegErasure : public MachineFunctionPass {
31 static char ID;
32 NVPTXProxyRegErasure() : MachineFunctionPass(ID) {}
33
34 bool runOnMachineFunction(MachineFunction &MF) override;
35
36 StringRef getPassName() const override {
37 return "NVPTX Proxy Register Instruction Erasure";
38 }
39
40 void getAnalysisUsage(AnalysisUsage &AU) const override {
41 MachineFunctionPass::getAnalysisUsage(AU);
42 }
43};
44
45} // namespace
46
47char NVPTXProxyRegErasure::ID = 0;
48
49INITIALIZE_PASS(NVPTXProxyRegErasure, "nvptx-proxyreg-erasure",
50 "NVPTX ProxyReg Erasure", false, false)
51
52bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {
53 SmallVector<MachineInstr *, 16> RemoveList;
54
55 // ProxyReg instructions forward a register as another: `%dst = mov.iN %src`.
56 // Bulk RAUW the `%dst` registers in two passes over the machine function.
57 DenseMap<Register, Register> RAUWBatch;
58
59 for (auto &BB : MF) {
60 for (auto &MI : BB) {
61 switch (MI.getOpcode()) {
62 case NVPTX::ProxyRegB1:
63 case NVPTX::ProxyRegB16:
64 case NVPTX::ProxyRegB32:
65 case NVPTX::ProxyRegB64: {
66 auto &InOp = *MI.uses().begin();
67 auto &OutOp = *MI.defs().begin();
68 assert(InOp.isReg() && "ProxyReg input should be a register.");
69 assert(OutOp.isReg() && "ProxyReg output should be a register.");
70 RemoveList.push_back(Elt: &MI);
71 Register replacement = InOp.getReg();
72 // Check if the replacement itself has been replaced.
73 if (auto it = RAUWBatch.find(Val: replacement); it != RAUWBatch.end())
74 replacement = it->second;
75 RAUWBatch.try_emplace(Key: OutOp.getReg(), Args&: replacement);
76 break;
77 }
78 }
79 }
80 }
81
82 // If there were no proxy instructions, exit early.
83 if (RemoveList.empty())
84 return false;
85
86 // Erase the proxy instructions first.
87 for (auto *MI : RemoveList) {
88 MI->eraseFromParent();
89 }
90
91 // Now go replace the registers and remove kill flags conservatively.
92 MachineRegisterInfo &MRI = MF.getRegInfo();
93 for (auto [From, To] : RAUWBatch) {
94 MRI.replaceRegWith(FromReg: From, ToReg: To);
95 MRI.clearKillFlags(Reg: To);
96 }
97
98 return true;
99}
100
101MachineFunctionPass *llvm::createNVPTXProxyRegErasurePass() {
102 return new NVPTXProxyRegErasure();
103}
104