[gcc r16-9320] aarch64: Extend comment about saving/restoring zt0

https://gcc.gnu.org/g:91f175c187adea112debb4bf415fc1e7447f3127

commit r16-9320-g91f175c187adea112debb4bf415fc1e7447f3127
Author: Alice Carlotti <[email protected]>
Date:   Thu Apr 16 12:37:53 2026 +0100

    aarch64: Extend comment about saving/restoring zt0
    
    Explain why aarch64_start_call_args only needs to save and restore zt0
    if the callee shares ZA state.
    
    gcc/ChangeLog:
    
            * config/aarch64/aarch64.cc (aarch64_start_call_args): Extend
            comment.

Diff:
---
 gcc/config/aarch64/aarch64.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 361b82ccd82d..ab8c6d0dff6e 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -12204,7 +12204,8 @@ aarch64_start_call_args (cumulative_args_t ca_v)
     emit_insn (gen_aarch64_start_private_za_call ());
 
   /* If this is a call to a shared-ZA function that doesn't share ZT0,
-     save and restore ZT0 around the call.  */
+     save and restore ZT0 around the call.  If ZA is not shared, then the
+     save/restore is instead emitted by aarch64_mode_emit_local_sme_state.  */
   if (aarch64_cfun_has_state ("zt0")
       && (ca->isa_mode & AARCH64_ISA_MODE_ZA_ON)
       && ca->shared_zt0_flags == 0)