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[CodeGen] Simplify ExpandPostRA::LowerSubregToReg. NFC. #179634

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Merged
jayfoad merged 3 commits into from
Feb 4, 2026
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[CodeGen] Simplify ExpandPostRA::LowerSubregToReg. NFC. #179634

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[CodeGen] Simplify ExpandPostRA::LowerSubregToReg. NFC.
jayfoad Feb 4, 2026
386e66b
clang-format
jayfoad Feb 4, 2026
d0d8177
Simplify more
jayfoad Feb 4, 2026
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32 changes: 14 additions & 18 deletions llvm/lib/CodeGen/ExpandPostRAPseudos.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -108,26 +108,22 @@ bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
// Watch out for case like this:
// %rax = SUBREG_TO_REG 0, killed %eax, 3
// We must leave %rax live.
if (DstReg != InsReg) {
MI->setDesc(TII->get(TargetOpcode::KILL));
MI->removeOperand(3); // SubIdx
MI->removeOperand(1); // Imm
LLVM_DEBUG(dbgs() << "subreg: replace by: " << *MI);
return true;
}
LLVM_DEBUG(dbgs() << "subreg: eliminated!");
} else {
TII->copyPhysReg(*MBB, MI, MI->getDebugLoc(), DstSubReg, InsReg,
MI->getOperand(2).isKill());

// Implicitly define DstReg for subsequent uses.
MachineBasicBlock::iterator CopyMI = MI;
--CopyMI;
CopyMI->addRegisterDefined(DstReg);
LLVM_DEBUG(dbgs() << "subreg: " << *CopyMI);
MI->setDesc(TII->get(TargetOpcode::KILL));
MI->removeOperand(3); // SubIdx
MI->removeOperand(1); // Imm
LLVM_DEBUG(dbgs() << "subreg: replaced by: " << *MI);
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@jayfoad jayfoad Feb 4, 2026

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I tweaked the tracing here for consistency ("replace" -> "replaced").

return true;
}

LLVM_DEBUG(dbgs() << '\n');
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@jayfoad jayfoad Feb 4, 2026

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I removed this for consistency.

TII->copyPhysReg(*MBB, MI, MI->getDebugLoc(), DstSubReg, InsReg,
MI->getOperand(2).isKill());

// Implicitly define DstReg for subsequent uses.
MachineBasicBlock::iterator CopyMI = MI;
--CopyMI;
CopyMI->addRegisterDefined(DstReg);
LLVM_DEBUG(dbgs() << "subreg: " << *CopyMI);

MBB->erase(MI);
return true;
}
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