[compiler-rt] 012097d - [compiler-rt][AArch64] Exit early from __arm_za_disable. (#174942)

[via llvm-commits]

Author: Sander de Smalen
Date: 2026-01-08T15:00:25Z
New Revision: 012097d4fe7f300a59f9d2b89e528e1bd449d4c1

URL: https://github.com/llvm/llvm-project/commit/012097d4fe7f300a59f9d2b89e528e1bd449d4c1
DIFF: https://github.com/llvm/llvm-project/commit/012097d4fe7f300a59f9d2b89e528e1bd449d4c1.diff

LOG: [compiler-rt][AArch64] Exit early from __arm_za_disable. (#174942)

Because `__arm_za_disable` is a private-ZA function, it's only ever
entered with ZA state `off` or `dormant`. If the state is `off` then we
can safely return and there is no need to call `__arm_tpidr2_save` or to
explicitly set PSTATE.ZA or TPIDR2_EL0 to zero.

Added: 
    

Modified: 
    compiler-rt/lib/builtins/aarch64/sme-abi.S

Removed: 
    


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diff  --git a/compiler-rt/lib/builtins/aarch64/sme-abi.S b/compiler-rt/lib/builtins/aarch64/sme-abi.S
index 1713a5969459a..465f1c763c0d3 100644
--- a/compiler-rt/lib/builtins/aarch64/sme-abi.S
+++ b/compiler-rt/lib/builtins/aarch64/sme-abi.S
@@ -161,6 +161,13 @@ DEFINE_COMPILERRT_FUNCTION(__arm_za_disable)
   ldr x14, [x14, CPU_FEATS_SYMBOL_OFFSET]
   tbz x14, #FEAT_SME_BIT, 0f
 
+  // If TPIDR2_EL0 is zero then nothing needs doing because
+  // __arm_za_disable is a private-ZA function and is only
+  // ever entered with ZA state 'off' or 'dormant', so
+  // we can assume PSTATE.ZA=0.
+  mrs x14, TPIDR2_EL0
+  cbz x14, 0f
+
   // Otherwise, the subroutine behaves as if it did the following:
   // * Call __arm_tpidr2_save.
   stp x29, x30, [sp, #-16]!