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[AArch64][SME] Disable tail calls for callees that require saving ZT0 #165371

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Merged
merged 2 commits into from
Oct 28, 2025
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[AArch64][SME] Disable tail calls for callees that require saving ZT0 #165371

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MacDue Oct 28, 2025
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[AArch64][SME] Disable tail calls for callees that require saving ZT0
MacDue Oct 28, 2025
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3 changes: 2 additions & 1 deletion llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -9028,11 +9028,12 @@ bool AArch64TargetLowering::isEligibleForTailCallOptimization(
CallingConv::ID CallerCC = CallerF.getCallingConv();

// SME Streaming functions are not eligible for TCO as they may require
// the streaming mode or ZA to be restored after returning from the call.
// the streaming mode or ZA/ZT0 to be restored after returning from the call.
SMECallAttrs CallAttrs =
getSMECallAttrs(CallerF, getRuntimeLibcallsInfo(), CLI);
if (CallAttrs.requiresSMChange() || CallAttrs.requiresLazySave() ||
CallAttrs.requiresPreservingAllZAState() ||
CallAttrs.requiresPreservingZT0() ||
CallAttrs.caller().hasStreamingBody())
return false;

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18 changes: 18 additions & 0 deletions llvm/test/CodeGen/AArch64/sme-zt0-state.ll
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Expand Up @@ -426,3 +426,21 @@ define void @zt0_multiple_private_za_calls(ptr %callee) "aarch64_in_zt0" nounwin
call void %callee()
ret void
}

define void @disable_tailcallopt(ptr %callee) "aarch64_inout_zt0" nounwind {
; CHECK-COMMON-LABEL: disable_tailcallopt:
; CHECK-COMMON: // %bb.0:
; CHECK-COMMON-NEXT: sub sp, sp, #80
; CHECK-COMMON-NEXT: stp x30, x19, [sp, #64] // 16-byte Folded Spill
; CHECK-COMMON-NEXT: mov x19, sp
; CHECK-COMMON-NEXT: str zt0, [x19]
; CHECK-COMMON-NEXT: smstop za
; CHECK-COMMON-NEXT: blr x0
; CHECK-COMMON-NEXT: smstart za
; CHECK-COMMON-NEXT: ldr zt0, [x19]
; CHECK-COMMON-NEXT: ldp x30, x19, [sp, #64] // 16-byte Folded Reload
; CHECK-COMMON-NEXT: add sp, sp, #80
; CHECK-COMMON-NEXT: ret
tail call void %callee()
ret void
}