llvm-project/llvm/lib/CodeGen/LowerSubregs.cpp

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//===-- LowerSubregs.cpp - Subregister Lowering instruction pass ----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines a MachineFunction pass which runs after register
// allocation that turns subreg insert/extract instructions into register
// copies, as needed. This ensures correct codegen even if the coalescer
// isn't able to remove all subreg instructions.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "lowersubregs"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
namespace {
struct LowerSubregsInstructionPass : public MachineFunctionPass {
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private:
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
public:
static char ID; // Pass identification, replacement for typeid
LowerSubregsInstructionPass() : MachineFunctionPass(&ID) {}
const char *getPassName() const {
return "Subregister lowering instruction pass";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - pass entry point
bool runOnMachineFunction(MachineFunction&);
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private:
bool LowerExtract(MachineInstr *MI);
bool LowerInsert(MachineInstr *MI);
bool LowerSubregToReg(MachineInstr *MI);
void TransferDeadFlag(MachineInstr *MI, unsigned DstReg,
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const TargetRegisterInfo *TRI);
void TransferKillFlag(MachineInstr *MI, unsigned SrcReg,
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const TargetRegisterInfo *TRI,
bool AddIfNotFound = false);
};
char LowerSubregsInstructionPass::ID = 0;
}
FunctionPass *llvm::createLowerSubregsPass() {
return new LowerSubregsInstructionPass();
}
/// TransferDeadFlag - MI is a pseudo-instruction with DstReg dead,
/// and the lowered replacement instructions immediately precede it.
/// Mark the replacement instructions with the dead flag.
void
LowerSubregsInstructionPass::TransferDeadFlag(MachineInstr *MI,
unsigned DstReg,
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const TargetRegisterInfo *TRI) {
for (MachineBasicBlock::iterator MII =
prior(MachineBasicBlock::iterator(MI)); ; --MII) {
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if (MII->addRegisterDead(DstReg, TRI))
break;
assert(MII != MI->getParent()->begin() &&
"copyRegToReg output doesn't reference destination register!");
}
}
/// TransferKillFlag - MI is a pseudo-instruction with SrcReg killed,
/// and the lowered replacement instructions immediately precede it.
/// Mark the replacement instructions with the kill flag.
void
LowerSubregsInstructionPass::TransferKillFlag(MachineInstr *MI,
unsigned SrcReg,
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const TargetRegisterInfo *TRI,
bool AddIfNotFound) {
for (MachineBasicBlock::iterator MII =
prior(MachineBasicBlock::iterator(MI)); ; --MII) {
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if (MII->addRegisterKilled(SrcReg, TRI, AddIfNotFound))
break;
assert(MII != MI->getParent()->begin() &&
"copyRegToReg output doesn't reference source register!");
}
}
bool LowerSubregsInstructionPass::LowerExtract(MachineInstr *MI) {
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MachineBasicBlock *MBB = MI->getParent();
LowerSubregsInstructionPass::LowerExtract should not extend the live range of registers. When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the kill flag to the place where the sub-register is killed. This can accidentally overlap with the use of a sibling sub-register, and we have trouble. In the test case we have this code: Live Ins: %R0 %R1 %R2 %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] %R1L<def> = EXTRACT_SUBREG %R1<kill>, 1 %R0L<def> = EXTRACT_SUBREG %R0<kill>, 1 %R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: eliminated! subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H: *** Bad machine code: Redefining a live physical register *** - function: f - basic block: 0x18358c0 (#0) - instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] Register R2H was defined but already live. The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating it completely: subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill> Note that these IMPLICIT_DEF instructions survive to the asm output. It is necessary to fix the stack-color-with-reg test case because of that. llvm-svn: 78093
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assert(MI->getOperand(0).isReg() && MI->getOperand(0).isDef() &&
MI->getOperand(1).isReg() && MI->getOperand(1).isUse() &&
MI->getOperand(2).isImm() && "Malformed extract_subreg");
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unsigned DstReg = MI->getOperand(0).getReg();
unsigned SuperReg = MI->getOperand(1).getReg();
unsigned SubIdx = MI->getOperand(2).getImm();
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unsigned SrcReg = TRI->getSubReg(SuperReg, SubIdx);
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assert(TargetRegisterInfo::isPhysicalRegister(SuperReg) &&
"Extract supperg source must be a physical register");
assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
"Extract destination must be in a physical register");
assert(SrcReg && "invalid subregister index for register");
LowerSubregsInstructionPass::LowerExtract should not extend the live range of registers. When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the kill flag to the place where the sub-register is killed. This can accidentally overlap with the use of a sibling sub-register, and we have trouble. In the test case we have this code: Live Ins: %R0 %R1 %R2 %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] %R1L<def> = EXTRACT_SUBREG %R1<kill>, 1 %R0L<def> = EXTRACT_SUBREG %R0<kill>, 1 %R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: eliminated! subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H: *** Bad machine code: Redefining a live physical register *** - function: f - basic block: 0x18358c0 (#0) - instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] Register R2H was defined but already live. The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating it completely: subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill> Note that these IMPLICIT_DEF instructions survive to the asm output. It is necessary to fix the stack-color-with-reg test case because of that. llvm-svn: 78093
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DEBUG(errs() << "subreg: CONVERTING: " << *MI);
if (SrcReg == DstReg) {
LowerSubregsInstructionPass::LowerExtract should not extend the live range of registers. When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the kill flag to the place where the sub-register is killed. This can accidentally overlap with the use of a sibling sub-register, and we have trouble. In the test case we have this code: Live Ins: %R0 %R1 %R2 %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] %R1L<def> = EXTRACT_SUBREG %R1<kill>, 1 %R0L<def> = EXTRACT_SUBREG %R0<kill>, 1 %R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: eliminated! subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H: *** Bad machine code: Redefining a live physical register *** - function: f - basic block: 0x18358c0 (#0) - instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] Register R2H was defined but already live. The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating it completely: subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill> Note that these IMPLICIT_DEF instructions survive to the asm output. It is necessary to fix the stack-color-with-reg test case because of that. llvm-svn: 78093
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// No need to insert an identity copy instruction.
if (MI->getOperand(1).isKill()) {
// We must make sure the super-register gets killed. Replace the
// instruction with KILL.
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MI->setDesc(TII->get(TargetInstrInfo::KILL));
LowerSubregsInstructionPass::LowerExtract should not extend the live range of registers. When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the kill flag to the place where the sub-register is killed. This can accidentally overlap with the use of a sibling sub-register, and we have trouble. In the test case we have this code: Live Ins: %R0 %R1 %R2 %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] %R1L<def> = EXTRACT_SUBREG %R1<kill>, 1 %R0L<def> = EXTRACT_SUBREG %R0<kill>, 1 %R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: eliminated! subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H: *** Bad machine code: Redefining a live physical register *** - function: f - basic block: 0x18358c0 (#0) - instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] Register R2H was defined but already live. The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating it completely: subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill> Note that these IMPLICIT_DEF instructions survive to the asm output. It is necessary to fix the stack-color-with-reg test case because of that. llvm-svn: 78093
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MI->RemoveOperand(2); // SubIdx
DEBUG(errs() << "subreg: replace by: " << *MI);
LowerSubregsInstructionPass::LowerExtract should not extend the live range of registers. When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the kill flag to the place where the sub-register is killed. This can accidentally overlap with the use of a sibling sub-register, and we have trouble. In the test case we have this code: Live Ins: %R0 %R1 %R2 %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] %R1L<def> = EXTRACT_SUBREG %R1<kill>, 1 %R0L<def> = EXTRACT_SUBREG %R0<kill>, 1 %R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: eliminated! subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H: *** Bad machine code: Redefining a live physical register *** - function: f - basic block: 0x18358c0 (#0) - instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] Register R2H was defined but already live. The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating it completely: subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill> Note that these IMPLICIT_DEF instructions survive to the asm output. It is necessary to fix the stack-color-with-reg test case because of that. llvm-svn: 78093
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return true;
}
DEBUG(errs() << "subreg: eliminated!");
} else {
// Insert copy
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const TargetRegisterClass *TRCS = TRI->getPhysicalRegisterRegClass(DstReg);
const TargetRegisterClass *TRCD = TRI->getPhysicalRegisterRegClass(SrcReg);
bool Emitted = TII->copyRegToReg(*MBB, MI, DstReg, SrcReg, TRCD, TRCS);
(void)Emitted;
assert(Emitted && "Subreg and Dst must be of compatible register class");
// Transfer the kill/dead flags, if needed.
if (MI->getOperand(0).isDead())
TransferDeadFlag(MI, DstReg, TRI);
if (MI->getOperand(1).isKill())
TransferKillFlag(MI, SuperReg, TRI, true);
DEBUG({
MachineBasicBlock::iterator dMI = MI;
errs() << "subreg: " << *(--dMI);
});
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}
DEBUG(errs() << '\n');
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MBB->erase(MI);
return true;
}
bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
MachineBasicBlock *MBB = MI->getParent();
assert((MI->getOperand(0).isReg() && MI->getOperand(0).isDef()) &&
MI->getOperand(1).isImm() &&
(MI->getOperand(2).isReg() && MI->getOperand(2).isUse()) &&
MI->getOperand(3).isImm() && "Invalid subreg_to_reg");
unsigned DstReg = MI->getOperand(0).getReg();
unsigned InsReg = MI->getOperand(2).getReg();
unsigned InsSIdx = MI->getOperand(2).getSubReg();
unsigned SubIdx = MI->getOperand(3).getImm();
assert(SubIdx != 0 && "Invalid index for insert_subreg");
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unsigned DstSubReg = TRI->getSubReg(DstReg, SubIdx);
assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
"Insert destination must be in a physical register");
assert(TargetRegisterInfo::isPhysicalRegister(InsReg) &&
"Inserted value must be in a physical register");
DEBUG(errs() << "subreg: CONVERTING: " << *MI);
if (DstSubReg == InsReg && InsSIdx == 0) {
// No need to insert an identify copy instruction.
// Watch out for case like this:
// %RAX<def> = ...
// %RAX<def> = SUBREG_TO_REG 0, %EAX:3<kill>, 3
// The first def is defining RAX, not EAX so the top bits were not
// zero extended.
DEBUG(errs() << "subreg: eliminated!");
} else {
// Insert sub-register copy
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const TargetRegisterClass *TRC0= TRI->getPhysicalRegisterRegClass(DstSubReg);
const TargetRegisterClass *TRC1= TRI->getPhysicalRegisterRegClass(InsReg);
bool Emitted = TII->copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
(void)Emitted;
assert(Emitted && "Subreg and Dst must be of compatible register class");
// Transfer the kill/dead flags, if needed.
if (MI->getOperand(0).isDead())
TransferDeadFlag(MI, DstSubReg, TRI);
if (MI->getOperand(2).isKill())
TransferKillFlag(MI, InsReg, TRI);
DEBUG({
MachineBasicBlock::iterator dMI = MI;
errs() << "subreg: " << *(--dMI);
});
}
DEBUG(errs() << '\n');
MBB->erase(MI);
return true;
}
bool LowerSubregsInstructionPass::LowerInsert(MachineInstr *MI) {
MachineBasicBlock *MBB = MI->getParent();
assert((MI->getOperand(0).isReg() && MI->getOperand(0).isDef()) &&
(MI->getOperand(1).isReg() && MI->getOperand(1).isUse()) &&
(MI->getOperand(2).isReg() && MI->getOperand(2).isUse()) &&
MI->getOperand(3).isImm() && "Invalid insert_subreg");
unsigned DstReg = MI->getOperand(0).getReg();
#ifndef NDEBUG
unsigned SrcReg = MI->getOperand(1).getReg();
#endif
unsigned InsReg = MI->getOperand(2).getReg();
unsigned SubIdx = MI->getOperand(3).getImm();
assert(DstReg == SrcReg && "insert_subreg not a two-address instruction?");
assert(SubIdx != 0 && "Invalid index for insert_subreg");
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unsigned DstSubReg = TRI->getSubReg(DstReg, SubIdx);
assert(DstSubReg && "invalid subregister index for register");
assert(TargetRegisterInfo::isPhysicalRegister(SrcReg) &&
"Insert superreg source must be in a physical register");
assert(TargetRegisterInfo::isPhysicalRegister(InsReg) &&
"Inserted value must be in a physical register");
DEBUG(errs() << "subreg: CONVERTING: " << *MI);
if (DstSubReg == InsReg) {
// No need to insert an identity copy instruction. If the SrcReg was
// <undef>, we need to make sure it is alive by inserting a KILL
if (MI->getOperand(1).isUndef() && !MI->getOperand(0).isDead()) {
MachineInstrBuilder MIB = BuildMI(*MBB, MI, MI->getDebugLoc(),
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TII->get(TargetInstrInfo::KILL), DstReg);
if (MI->getOperand(2).isUndef())
MIB.addReg(InsReg, RegState::Undef);
else
MIB.addReg(InsReg, RegState::Kill);
} else {
DEBUG(errs() << "subreg: eliminated!\n");
MBB->erase(MI);
return true;
}
} else {
// Insert sub-register copy
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const TargetRegisterClass *TRC0= TRI->getPhysicalRegisterRegClass(DstSubReg);
const TargetRegisterClass *TRC1= TRI->getPhysicalRegisterRegClass(InsReg);
if (MI->getOperand(2).isUndef())
// If the source register being inserted is undef, then this becomes a
// KILL.
BuildMI(*MBB, MI, MI->getDebugLoc(),
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TII->get(TargetInstrInfo::KILL), DstSubReg);
else {
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bool Emitted = TII->copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
(void)Emitted;
assert(Emitted && "Subreg and Dst must be of compatible register class");
}
MachineBasicBlock::iterator CopyMI = MI;
--CopyMI;
// INSERT_SUBREG is a two-address instruction so it implicitly kills SrcReg.
if (!MI->getOperand(1).isUndef())
CopyMI->addOperand(MachineOperand::CreateReg(DstReg, false, true, true));
// Transfer the kill/dead flags, if needed.
if (MI->getOperand(0).isDead()) {
TransferDeadFlag(MI, DstSubReg, TRI);
} else {
// Make sure the full DstReg is live after this replacement.
CopyMI->addOperand(MachineOperand::CreateReg(DstReg, true, true));
}
// Make sure the inserted register gets killed
if (MI->getOperand(2).isKill() && !MI->getOperand(2).isUndef())
TransferKillFlag(MI, InsReg, TRI);
}
DEBUG({
MachineBasicBlock::iterator dMI = MI;
errs() << "subreg: " << *(--dMI) << "\n";
});
MBB->erase(MI);
return true;
}
/// runOnMachineFunction - Reduce subregister inserts and extracts to register
/// copies.
///
bool LowerSubregsInstructionPass::runOnMachineFunction(MachineFunction &MF) {
DEBUG(errs() << "Machine Function\n"
<< "********** LOWERING SUBREG INSTRS **********\n"
<< "********** Function: "
<< MF.getFunction()->getName() << '\n');
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TRI = MF.getTarget().getRegisterInfo();
TII = MF.getTarget().getInstrInfo();
bool MadeChange = false;
for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end();
mbbi != mbbe; ++mbbi) {
for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
mi != me;) {
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MachineBasicBlock::iterator nmi = next(mi);
MachineInstr *MI = mi;
if (MI->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG) {
MadeChange |= LowerExtract(MI);
} else if (MI->getOpcode() == TargetInstrInfo::INSERT_SUBREG) {
MadeChange |= LowerInsert(MI);
} else if (MI->getOpcode() == TargetInstrInfo::SUBREG_TO_REG) {
MadeChange |= LowerSubregToReg(MI);
}
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mi = nmi;
}
}
return MadeChange;
}