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/MachineFunctionPass.h"
15#include "llvm/CodeGen/MachineInstr.h"
16#include "llvm/CodeGen/Passes.h"
17#include "llvm/CodeGen/TargetInstrInfo.h"
18#include "llvm/CodeGen/TargetRegisterInfo.h"
19#include "llvm/CodeGen/TargetSubtargetInfo.h"
20#include "llvm/InitializePasses.h"
21#include "llvm/Support/Debug.h"
22#include "llvm/Support/raw_ostream.h"
23
24using namespace llvm;
25
26#define DEBUG_TYPE "postrapseudos"
27
28namespace {
29struct ExpandPostRA : public MachineFunctionPass {
30private:
31 const TargetRegisterInfo *TRI = nullptr;
32 const TargetInstrInfo *TII = nullptr;
33
34public:
35 static char ID; // Pass identification, replacement for typeid
36 ExpandPostRA() : MachineFunctionPass(ID) {}
37
38 void getAnalysisUsage(AnalysisUsage &AU) const override {
39 AU.setPreservesCFG();
40 AU.addPreservedID(ID&: MachineLoopInfoID);
41 AU.addPreservedID(ID&: MachineDominatorsID);
42 MachineFunctionPass::getAnalysisUsage(AU);
43 }
44
45 /// runOnMachineFunction - pass entry point
46 bool runOnMachineFunction(MachineFunction&) override;
47
48private:
49 bool LowerSubregToReg(MachineInstr *MI);
50};
51} // end anonymous namespace
52
53char ExpandPostRA::ID = 0;
54char &llvm::ExpandPostRAPseudosID = ExpandPostRA::ID;
55
56INITIALIZE_PASS(ExpandPostRA, DEBUG_TYPE,
57 "Post-RA pseudo instruction expansion pass", false, false)
58
59bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
60 MachineBasicBlock *MBB = MI->getParent();
61 assert((MI->getOperand(0).isReg() && MI->getOperand(0).isDef()) &&
62 MI->getOperand(1).isImm() &&
63 (MI->getOperand(2).isReg() && MI->getOperand(2).isUse()) &&
64 MI->getOperand(3).isImm() && "Invalid subreg_to_reg");
65
66 Register DstReg = MI->getOperand(i: 0).getReg();
67 Register InsReg = MI->getOperand(i: 2).getReg();
68 assert(!MI->getOperand(2).getSubReg() && "SubIdx on physreg?");
69 unsigned SubIdx = MI->getOperand(i: 3).getImm();
70
71 assert(SubIdx != 0 && "Invalid index for insert_subreg");
72 Register DstSubReg = TRI->getSubReg(Reg: DstReg, Idx: SubIdx);
73
74 assert(DstReg.isPhysical() &&
75 "Insert destination must be in a physical register");
76 assert(InsReg.isPhysical() &&
77 "Inserted value must be in a physical register");
78
79 LLVM_DEBUG(dbgs() << "subreg: CONVERTING: " << *MI);
80
81 if (MI->allDefsAreDead()) {
82 MI->setDesc(TII->get(Opcode: TargetOpcode::KILL));
83 MI->removeOperand(OpNo: 3); // SubIdx
84 MI->removeOperand(OpNo: 1); // Imm
85 LLVM_DEBUG(dbgs() << "subreg: replaced by: " << *MI);
86 return true;
87 }
88
89 if (DstSubReg == InsReg) {
90 // No need to insert an identity copy instruction.
91 // Watch out for case like this:
92 // %rax = SUBREG_TO_REG 0, killed %eax, 3
93 // We must leave %rax live.
94 if (DstReg != InsReg) {
95 MI->setDesc(TII->get(Opcode: TargetOpcode::KILL));
96 MI->removeOperand(OpNo: 3); // SubIdx
97 MI->removeOperand(OpNo: 1); // Imm
98 LLVM_DEBUG(dbgs() << "subreg: replace by: " << *MI);
99 return true;
100 }
101 LLVM_DEBUG(dbgs() << "subreg: eliminated!");
102 } else {
103 TII->copyPhysReg(MBB&: *MBB, MI, DL: MI->getDebugLoc(), DestReg: DstSubReg, SrcReg: InsReg,
104 KillSrc: MI->getOperand(i: 2).isKill());
105
106 // Implicitly define DstReg for subsequent uses.
107 MachineBasicBlock::iterator CopyMI = MI;
108 --CopyMI;
109 CopyMI->addRegisterDefined(Reg: DstReg);
110 LLVM_DEBUG(dbgs() << "subreg: " << *CopyMI);
111 }
112
113 LLVM_DEBUG(dbgs() << '\n');
114 MBB->erase(I: MI);
115 return true;
116}
117
118/// runOnMachineFunction - Reduce subregister inserts and extracts to register
119/// copies.
120///
121bool ExpandPostRA::runOnMachineFunction(MachineFunction &MF) {
122 LLVM_DEBUG(dbgs() << "Machine Function\n"
123 << "********** EXPANDING POST-RA PSEUDO INSTRS **********\n"
124 << "********** Function: " << MF.getName() << '\n');
125 TRI = MF.getSubtarget().getRegisterInfo();
126 TII = MF.getSubtarget().getInstrInfo();
127
128 bool MadeChange = false;
129
130 for (MachineBasicBlock &MBB : MF) {
131 for (MachineInstr &MI : llvm::make_early_inc_range(Range&: MBB)) {
132 // Only expand pseudos.
133 if (!MI.isPseudo())
134 continue;
135
136 // Give targets a chance to expand even standard pseudos.
137 if (TII->expandPostRAPseudo(MI)) {
138 MadeChange = true;
139 continue;
140 }
141
142 // Expand standard pseudos.
143 switch (MI.getOpcode()) {
144 case TargetOpcode::SUBREG_TO_REG:
145 MadeChange |= LowerSubregToReg(MI: &MI);
146 break;
147 case TargetOpcode::COPY:
148 TII->lowerCopy(MI: &MI, TRI);
149 MadeChange = true;
150 break;
151 case TargetOpcode::DBG_VALUE:
152 continue;
153 case TargetOpcode::INSERT_SUBREG:
154 case TargetOpcode::EXTRACT_SUBREG:
155 llvm_unreachable("Sub-register pseudos should have been eliminated.");
156 }
157 }
158 }
159
160 return MadeChange;
161}
162