1 //=== LoongArchDeadRegisterDefinitions.cpp - Replace dead defs w/ zero reg ===//
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 // This pass rewrites Rd to r0 for instrs whose return values are unused.
10 //
11 //===---------------------------------------------------------------------===//
12
13 #include "LoongArch.h"
14 #include "LoongArchInstrInfo.h"
15 #include "LoongArchSubtarget.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/CodeGen/LiveDebugVariables.h"
18 #include "llvm/CodeGen/LiveIntervals.h"
19 #include "llvm/CodeGen/LiveStacks.h"
20 #include "llvm/CodeGen/MachineFunctionPass.h"
21 #include "llvm/CodeGen/MachineRegisterInfo.h"
22
23 using namespace llvm;
24 #define DEBUG_TYPE "loongarch-dead-defs"
25 #define LoongArch_DEAD_REG_DEF_NAME "LoongArch Dead register definitions"
26
27 STATISTIC(NumDeadDefsReplaced, "Number of dead definitions replaced");
28
29 namespace {
30 class LoongArchDeadRegisterDefinitions : public MachineFunctionPass {
31 public:
32 static char ID;
33
LoongArchDeadRegisterDefinitions()34 LoongArchDeadRegisterDefinitions() : MachineFunctionPass(ID) {}
35 bool runOnMachineFunction(MachineFunction &MF) override;
getAnalysisUsage(AnalysisUsage & AU) const36 void getAnalysisUsage(AnalysisUsage &AU) const override {
37 AU.setPreservesCFG();
38 AU.addRequired<LiveIntervalsWrapperPass>();
39 AU.addPreserved<LiveIntervalsWrapperPass>();
40 AU.addRequired<LiveIntervalsWrapperPass>();
41 AU.addPreserved<SlotIndexesWrapperPass>();
42 AU.addPreserved<LiveDebugVariables>();
43 AU.addPreserved<LiveStacks>();
44 MachineFunctionPass::getAnalysisUsage(AU);
45 }
46
getPassName() const47 StringRef getPassName() const override { return LoongArch_DEAD_REG_DEF_NAME; }
48 };
49 } // end anonymous namespace
50
51 char LoongArchDeadRegisterDefinitions::ID = 0;
INITIALIZE_PASS(LoongArchDeadRegisterDefinitions,DEBUG_TYPE,LoongArch_DEAD_REG_DEF_NAME,false,false)52 INITIALIZE_PASS(LoongArchDeadRegisterDefinitions, DEBUG_TYPE,
53 LoongArch_DEAD_REG_DEF_NAME, false, false)
54
55 FunctionPass *llvm::createLoongArchDeadRegisterDefinitionsPass() {
56 return new LoongArchDeadRegisterDefinitions();
57 }
58
runOnMachineFunction(MachineFunction & MF)59 bool LoongArchDeadRegisterDefinitions::runOnMachineFunction(
60 MachineFunction &MF) {
61 if (skipFunction(MF.getFunction()))
62 return false;
63
64 const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
65 const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
66 LiveIntervals &LIS = getAnalysis<LiveIntervalsWrapperPass>().getLIS();
67 LLVM_DEBUG(dbgs() << "***** LoongArchDeadRegisterDefinitions *****\n");
68
69 bool MadeChange = false;
70 for (MachineBasicBlock &MBB : MF) {
71 for (MachineInstr &MI : MBB) {
72 // We only handle non-computational instructions.
73 const MCInstrDesc &Desc = MI.getDesc();
74 if (!Desc.mayLoad() && !Desc.mayStore() &&
75 !Desc.hasUnmodeledSideEffects())
76 continue;
77 for (int I = 0, E = Desc.getNumDefs(); I != E; ++I) {
78 MachineOperand &MO = MI.getOperand(I);
79 if (!MO.isReg() || !MO.isDef() || MO.isEarlyClobber())
80 continue;
81 // Be careful not to change the register if it's a tied operand.
82 if (MI.isRegTiedToUseOperand(I)) {
83 LLVM_DEBUG(dbgs() << " Ignoring, def is tied operand.\n");
84 continue;
85 }
86 Register Reg = MO.getReg();
87 if (!Reg.isVirtual() || !MO.isDead())
88 continue;
89 LLVM_DEBUG(dbgs() << " Dead def operand #" << I << " in:\n ";
90 MI.print(dbgs()));
91 const TargetRegisterClass *RC = TII->getRegClass(Desc, I, TRI, MF);
92 if (!(RC && RC->contains(LoongArch::R0))) {
93 LLVM_DEBUG(dbgs() << " Ignoring, register is not a GPR.\n");
94 continue;
95 }
96 assert(LIS.hasInterval(Reg));
97 LIS.removeInterval(Reg);
98 MO.setReg(LoongArch::R0);
99 LLVM_DEBUG(dbgs() << " Replacing with zero register. New:\n ";
100 MI.print(dbgs()));
101 ++NumDeadDefsReplaced;
102 MadeChange = true;
103 }
104 }
105 }
106
107 return MadeChange;
108 }
109