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[AArch64] Fix missing register definitions in homogeneous epilog lowering #171118

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Merged
kyulee-com merged 1 commit into from
Dec 9, 2025
Merged

[AArch64] Fix missing register definitions in homogeneous epilog lowering #171118

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27 changes: 17 additions & 10 deletions llvm/lib/Target/AArch64/AArch64LowerHomogeneousPrologEpilog.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -483,27 +483,28 @@ bool AArch64LowerHomogeneousPE::lowerEpilog(
assert(MI.getOpcode() == AArch64::HOM_Epilog);

auto Return = NextMBBI;
MachineInstr *HelperCall = nullptr;
if (shouldUseFrameHelper(MBB, NextMBBI, Regs, FrameHelperType::EpilogTail)) {
// When MBB ends with a return, emit a tail-call to the epilog helper
auto *EpilogTailHelper =
getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::EpilogTail);
BuildMI(MBB, MBBI, DL, TII->get(AArch64::TCRETURNdi))
.addGlobalAddress(EpilogTailHelper)
.addImm(0)
.setMIFlag(MachineInstr::FrameDestroy)
.copyImplicitOps(MI)
.copyImplicitOps(*Return);
HelperCall = BuildMI(MBB, MBBI, DL, TII->get(AArch64::TCRETURNdi))
.addGlobalAddress(EpilogTailHelper)
.addImm(0)
.setMIFlag(MachineInstr::FrameDestroy)
.copyImplicitOps(MI)
.copyImplicitOps(*Return);
NextMBBI = std::next(Return);
Return->removeFromParent();
} else if (shouldUseFrameHelper(MBB, NextMBBI, Regs,
FrameHelperType::Epilog)) {
// The default epilog helper case.
auto *EpilogHelper =
getOrCreateFrameHelper(M, MMI, Regs, FrameHelperType::Epilog);
BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
.addGlobalAddress(EpilogHelper)
.setMIFlag(MachineInstr::FrameDestroy)
.copyImplicitOps(MI);
HelperCall = BuildMI(MBB, MBBI, DL, TII->get(AArch64::BL))
.addGlobalAddress(EpilogHelper)
.setMIFlag(MachineInstr::FrameDestroy)
.copyImplicitOps(MI);
} else {
// Fall back to no-helper.
for (int I = 0; I < Size - 2; I += 2)
Expand All @@ -512,6 +513,12 @@ bool AArch64LowerHomogeneousPE::lowerEpilog(
emitLoad(MF, MBB, MBBI, *TII, Regs[Size - 2], Regs[Size - 1], Size, true);
}

// Make sure all explicit definitions are preserved in the helper call;
// implicit ones are already handled by copyImplicitOps.
if (HelperCall)
for (auto &Def : MBBI->defs())
HelperCall->addRegisterDefined(Def.getReg(),
MF.getRegInfo().getTargetRegisterInfo());
MBBI->removeFromParent();
return true;
}
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28 changes: 28 additions & 0 deletions llvm/test/CodeGen/AArch64/arm64-homogeneous-prolog-epilog-tail-call.mir
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@@ -0,0 +1,28 @@
# RUN: llc -verify-machineinstrs -mtriple=arm64-applie-ios7.0 -start-before=aarch64-lower-homogeneous-prolog-epilog -homogeneous-prolog-epilog %s
#
# This test ensures defined registers are preserved after lowering homogeneous
# epilog into helper calls. Without the fix, the verifier would complain about
# X20 being used by use_x20 without being defined.
--- |
define void @foo() {
entry:
ret void
}
declare void @use_x20()
...
---
name: foo
alignment: 4
tracksRegLiveness: true
liveins:
- { reg: '$x0' }
- { reg: '$x20' }
body: |
bb.0:
liveins: $x0, $x20, $lr, $x19, $x20
frame-setup HOM_Prolog $lr, $fp, $x19, $x20, 16
$sp = frame-setup SUBXri $sp, 32, 0
bb.1:
$sp = frame-destroy ADDXri $sp, 32, 0
$lr, $fp, $x19, $x20 = frame-destroy HOM_Epilog
TCRETURNdi @use_x20, 0, csr_aarch64_aapcs, implicit $sp, implicit $x20
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