[AArch64][SME] Disable tail calls in new ZA/ZT0 functions#177152
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Allowing this can result in invalid tail calls to shared ZA functions. It may be possible to limit this to the case where the caller is private ZA and the callee shares ZA, but for now it is generally disabled.
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@llvm/pr-subscribers-backend-aarch64 Author: Benjamin Maxwell (MacDue) ChangesAllowing this can result in invalid tail calls to shared ZA functions. It may be possible to limit this to the case where the caller is private ZA and the callee shares ZA, but for now it is generally disabled. 2 Files Affected:
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 2e96abfce72df..f16aa0188f9d5 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -9359,7 +9359,8 @@ bool AArch64TargetLowering::isEligibleForTailCallOptimization(
if (CallAttrs.requiresSMChange() || CallAttrs.requiresLazySave() ||
CallAttrs.requiresPreservingAllZAState() ||
CallAttrs.requiresPreservingZT0() ||
- CallAttrs.caller().hasStreamingBody())
+ CallAttrs.caller().hasStreamingBody() || CallAttrs.caller().isNewZA() ||
+ CallAttrs.caller().isNewZT0())
return false;
// Functions using the C or Fast calling convention that have an SVE signature
diff --git a/llvm/test/CodeGen/AArch64/sme-new-za-zt0-no-tail-call.ll b/llvm/test/CodeGen/AArch64/sme-new-za-zt0-no-tail-call.ll
new file mode 100644
index 0000000000000..3c76132556600
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/sme-new-za-zt0-no-tail-call.ll
@@ -0,0 +1,78 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sme2 -O3 -verify-machineinstrs < %s | FileCheck %s
+
+declare void @inout_za_zt0() "aarch64_inout_za" "aarch64_inout_zt0"
+
+define void @new_za_zt0() "aarch64_new_za" "aarch64_new_zt0" {
+; CHECK-LABEL: new_za_zt0:
+; CHECK: // %bb.0: // %entry
+; CHECK-NEXT: str x30, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-NEXT: .cfi_def_cfa_offset 16
+; CHECK-NEXT: .cfi_offset w30, -16
+; CHECK-NEXT: mrs x8, TPIDR2_EL0
+; CHECK-NEXT: cbz x8, .LBB0_2
+; CHECK-NEXT: // %bb.1: // %entry
+; CHECK-NEXT: bl __arm_tpidr2_save
+; CHECK-NEXT: msr TPIDR2_EL0, xzr
+; CHECK-NEXT: zero {za}
+; CHECK-NEXT: zero { zt0 }
+; CHECK-NEXT: .LBB0_2: // %entry
+; CHECK-NEXT: smstart za
+; CHECK-NEXT: bl inout_za_zt0
+; CHECK-NEXT: smstop za
+; CHECK-NEXT: ldr x30, [sp], #16 // 8-byte Folded Reload
+; CHECK-NEXT: ret
+entry:
+ tail call void @inout_za_zt0()
+ ret void
+}
+
+declare void @inout_za() "aarch64_inout_za"
+
+define void @new_za() "aarch64_new_za" {
+; CHECK-LABEL: new_za:
+; CHECK: // %bb.0: // %entry
+; CHECK-NEXT: str x30, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-NEXT: .cfi_def_cfa_offset 16
+; CHECK-NEXT: .cfi_offset w30, -16
+; CHECK-NEXT: mrs x8, TPIDR2_EL0
+; CHECK-NEXT: cbz x8, .LBB1_2
+; CHECK-NEXT: // %bb.1: // %entry
+; CHECK-NEXT: bl __arm_tpidr2_save
+; CHECK-NEXT: msr TPIDR2_EL0, xzr
+; CHECK-NEXT: zero {za}
+; CHECK-NEXT: .LBB1_2: // %entry
+; CHECK-NEXT: smstart za
+; CHECK-NEXT: bl inout_za
+; CHECK-NEXT: smstop za
+; CHECK-NEXT: ldr x30, [sp], #16 // 8-byte Folded Reload
+; CHECK-NEXT: ret
+entry:
+ tail call void @inout_za()
+ ret void
+}
+
+declare void @inout_zt0() "aarch64_inout_zt0"
+
+define void @new_zt0() "aarch64_new_zt0" {
+; CHECK-LABEL: new_zt0:
+; CHECK: // %bb.0: // %entry
+; CHECK-NEXT: str x30, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-NEXT: .cfi_def_cfa_offset 16
+; CHECK-NEXT: .cfi_offset w30, -16
+; CHECK-NEXT: mrs x8, TPIDR2_EL0
+; CHECK-NEXT: cbz x8, .LBB2_2
+; CHECK-NEXT: // %bb.1: // %entry
+; CHECK-NEXT: bl __arm_tpidr2_save
+; CHECK-NEXT: msr TPIDR2_EL0, xzr
+; CHECK-NEXT: zero { zt0 }
+; CHECK-NEXT: .LBB2_2: // %entry
+; CHECK-NEXT: smstart za
+; CHECK-NEXT: bl inout_zt0
+; CHECK-NEXT: smstop za
+; CHECK-NEXT: ldr x30, [sp], #16 // 8-byte Folded Reload
+; CHECK-NEXT: ret
+entry:
+ tail call void @inout_zt0()
+ ret void
+}
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sdesmalen-arm
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Jan 21, 2026
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Good find! I hope this was the last of them.
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/cherry-pick 10aca26 |
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/pull-request #177169 |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/59/builds/30443 Here is the relevant piece of the build log for the reference |
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Jan 22, 2026
Allowing this can result in invalid tail calls to shared ZA functions. It may be possible to limit this to the case where the caller is private ZA and the callee shares ZA, but for now it is generally disabled. (cherry picked from commit 10aca26)
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Allowing this can result in invalid tail calls to shared ZA functions.
It may be possible to limit this to the case where the caller is private ZA and the callee shares ZA, but for now it is generally disabled.