1 //===-- ExpandPostRAPseudos.cpp - Pseudo instruction expansion pass -------===//
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 file defines a pass that expands COPY and SUBREG_TO_REG pseudo
10 // instructions after register allocation.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/CodeGen/ExpandPostRAPseudos.h"
15 #include "llvm/CodeGen/MachineDominators.h"
16 #include "llvm/CodeGen/MachineFunctionPass.h"
17 #include "llvm/CodeGen/MachineInstr.h"
18 #include "llvm/CodeGen/MachineLoopInfo.h"
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/CodeGen/TargetInstrInfo.h"
21 #include "llvm/CodeGen/TargetRegisterInfo.h"
22 #include "llvm/CodeGen/TargetSubtargetInfo.h"
23 #include "llvm/InitializePasses.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/raw_ostream.h"
26
27 using namespace llvm;
28
29 #define DEBUG_TYPE "postrapseudos"
30
31 namespace {
32 struct ExpandPostRA {
33 bool run(MachineFunction &);
34
35 private:
36 const TargetRegisterInfo *TRI = nullptr;
37 const TargetInstrInfo *TII = nullptr;
38
39 bool LowerSubregToReg(MachineInstr *MI);
40 };
41
42 struct ExpandPostRALegacy : public MachineFunctionPass {
43 static char ID;
ExpandPostRALegacy__anon00dfe2d00111::ExpandPostRALegacy44 ExpandPostRALegacy() : MachineFunctionPass(ID) {
45 initializeExpandPostRALegacyPass(*PassRegistry::getPassRegistry());
46 }
47
getAnalysisUsage__anon00dfe2d00111::ExpandPostRALegacy48 void getAnalysisUsage(AnalysisUsage &AU) const override {
49 AU.setPreservesCFG();
50 AU.addPreservedID(MachineLoopInfoID);
51 AU.addPreservedID(MachineDominatorsID);
52 MachineFunctionPass::getAnalysisUsage(AU);
53 }
54
55 /// runOnMachineFunction - pass entry point
56 bool runOnMachineFunction(MachineFunction &) override;
57 };
58 } // end anonymous namespace
59
60 PreservedAnalyses
run(MachineFunction & MF,MachineFunctionAnalysisManager & MFAM)61 ExpandPostRAPseudosPass::run(MachineFunction &MF,
62 MachineFunctionAnalysisManager &MFAM) {
63 if (!ExpandPostRA().run(MF))
64 return PreservedAnalyses::all();
65
66 return getMachineFunctionPassPreservedAnalyses()
67 .preserveSet<CFGAnalyses>()
68 .preserve<MachineLoopAnalysis>()
69 .preserve<MachineDominatorTreeAnalysis>();
70 }
71
72 char ExpandPostRALegacy::ID = 0;
73 char &llvm::ExpandPostRAPseudosID = ExpandPostRALegacy::ID;
74
75 INITIALIZE_PASS(ExpandPostRALegacy, DEBUG_TYPE,
76 "Post-RA pseudo instruction expansion pass", false, false)
77
LowerSubregToReg(MachineInstr * MI)78 bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
79 MachineBasicBlock *MBB = MI->getParent();
80 assert((MI->getOperand(0).isReg() && MI->getOperand(0).isDef()) &&
81 MI->getOperand(1).isImm() &&
82 (MI->getOperand(2).isReg() && MI->getOperand(2).isUse()) &&
83 MI->getOperand(3).isImm() && "Invalid subreg_to_reg");
84
85 Register DstReg = MI->getOperand(0).getReg();
86 Register InsReg = MI->getOperand(2).getReg();
87 assert(!MI->getOperand(2).getSubReg() && "SubIdx on physreg?");
88 unsigned SubIdx = MI->getOperand(3).getImm();
89
90 assert(SubIdx != 0 && "Invalid index for insert_subreg");
91 Register DstSubReg = TRI->getSubReg(DstReg, SubIdx);
92
93 assert(DstReg.isPhysical() &&
94 "Insert destination must be in a physical register");
95 assert(InsReg.isPhysical() &&
96 "Inserted value must be in a physical register");
97
98 LLVM_DEBUG(dbgs() << "subreg: CONVERTING: " << *MI);
99
100 if (MI->allDefsAreDead()) {
101 MI->setDesc(TII->get(TargetOpcode::KILL));
102 MI->removeOperand(3); // SubIdx
103 MI->removeOperand(1); // Imm
104 LLVM_DEBUG(dbgs() << "subreg: replaced by: " << *MI);
105 return true;
106 }
107
108 if (DstSubReg == InsReg) {
109 // No need to insert an identity copy instruction.
110 // Watch out for case like this:
111 // %rax = SUBREG_TO_REG 0, killed %eax, 3
112 // We must leave %rax live.
113 if (DstReg != InsReg) {
114 MI->setDesc(TII->get(TargetOpcode::KILL));
115 MI->removeOperand(3); // SubIdx
116 MI->removeOperand(1); // Imm
117 LLVM_DEBUG(dbgs() << "subreg: replace by: " << *MI);
118 return true;
119 }
120 LLVM_DEBUG(dbgs() << "subreg: eliminated!");
121 } else {
122 TII->copyPhysReg(*MBB, MI, MI->getDebugLoc(), DstSubReg, InsReg,
123 MI->getOperand(2).isKill());
124
125 // Implicitly define DstReg for subsequent uses.
126 MachineBasicBlock::iterator CopyMI = MI;
127 --CopyMI;
128 CopyMI->addRegisterDefined(DstReg);
129 LLVM_DEBUG(dbgs() << "subreg: " << *CopyMI);
130 }
131
132 LLVM_DEBUG(dbgs() << '\n');
133 MBB->erase(MI);
134 return true;
135 }
136
runOnMachineFunction(MachineFunction & MF)137 bool ExpandPostRALegacy::runOnMachineFunction(MachineFunction &MF) {
138 return ExpandPostRA().run(MF);
139 }
140
141 /// runOnMachineFunction - Reduce subregister inserts and extracts to register
142 /// copies.
143 ///
run(MachineFunction & MF)144 bool ExpandPostRA::run(MachineFunction &MF) {
145 LLVM_DEBUG(dbgs() << "Machine Function\n"
146 << "********** EXPANDING POST-RA PSEUDO INSTRS **********\n"
147 << "********** Function: " << MF.getName() << '\n');
148 TRI = MF.getSubtarget().getRegisterInfo();
149 TII = MF.getSubtarget().getInstrInfo();
150
151 bool MadeChange = false;
152
153 for (MachineBasicBlock &MBB : MF) {
154 for (MachineInstr &MI : llvm::make_early_inc_range(MBB)) {
155 // Only expand pseudos.
156 if (!MI.isPseudo())
157 continue;
158
159 // Give targets a chance to expand even standard pseudos.
160 if (TII->expandPostRAPseudo(MI)) {
161 MadeChange = true;
162 continue;
163 }
164
165 // Expand standard pseudos.
166 switch (MI.getOpcode()) {
167 case TargetOpcode::SUBREG_TO_REG:
168 MadeChange |= LowerSubregToReg(&MI);
169 break;
170 case TargetOpcode::COPY:
171 TII->lowerCopy(&MI, TRI);
172 MadeChange = true;
173 break;
174 case TargetOpcode::DBG_VALUE:
175 continue;
176 case TargetOpcode::INSERT_SUBREG:
177 case TargetOpcode::EXTRACT_SUBREG:
178 llvm_unreachable("Sub-register pseudos should have been eliminated.");
179 }
180 }
181 }
182
183 return MadeChange;
184 }
185