From: Alice Carlotti <alice.carlotti@arm.com>
Date: Thu, 16 Apr 2026 12:02:35 +0000 (+0100)
Subject: aarch64: Fix ZA state transition [PR119210]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=960c8597962a9816fd992072bcb911566dbb58ea;p=thirdparty%2Fgcc.git

aarch64: Fix ZA state transition [PR119210]

In the INACTIVE_CALLER -> INACTIVE LOCAL transition, ensure ZA is active
and zeroed before setting tpidr2_el0.

gcc/ChangeLog:

	PR target/119210
	* config/aarch64/aarch64.cc (aarch64_mode_emit_local_sme_state):
	Add PSTATE.ZA enablement, and zero it if already enabled.

gcc/testsuite/ChangeLog:

	PR target/119210
	* gcc.target/aarch64/sme/za_state_8.c: New test.
---

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 62194b96450..693ce8b4d25 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -31951,7 +31951,8 @@ aarch64_mode_emit_local_sme_state (aarch64_local_sme_state mode,
       emit_insn (gen_aarch64_tpidr2_save ());
       emit_insn (gen_aarch64_clear_tpidr2 ());
       if (mode == aarch64_local_sme_state::ACTIVE_LIVE
-	  || mode == aarch64_local_sme_state::ACTIVE_DEAD)
+	  || mode == aarch64_local_sme_state::ACTIVE_DEAD
+	  || mode == aarch64_local_sme_state::INACTIVE_LOCAL)
 	{
 	  if (aarch64_cfun_has_state ("za"))
 	    emit_insn (gen_aarch64_initial_zero_za ());
@@ -32033,6 +32034,16 @@ aarch64_mode_emit_local_sme_state (aarch64_local_sme_state mode,
 
   if (mode == aarch64_local_sme_state::INACTIVE_LOCAL)
     {
+      if (prev_mode == aarch64_local_sme_state::INACTIVE_CALLER)
+	/* Enable ZA (if it wasn't already enabled on entry).  Enabling ZA has
+	   the side-effect of zeroing ZA.
+
+	   A functionally correct alternative would be to leave TPIDR2_EL0 null
+	   and zero the save buffer.  However, zeroing the save buffer would require
+	   more code and would optimize for the case in which a callee also
+	   initialises private ZA state (which should be a rare event).  */
+	emit_insn (gen_aarch64_smstart_za ());
+
       if (prev_mode == aarch64_local_sme_state::ACTIVE_LIVE
 	  || prev_mode == aarch64_local_sme_state::ACTIVE_DEAD
 	  || prev_mode == aarch64_local_sme_state::INACTIVE_CALLER)
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/za_state_8.c b/gcc/testsuite/gcc.target/aarch64/sme/za_state_8.c
new file mode 100644
index 00000000000..9b7a6ffa69c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sme/za_state_8.c
@@ -0,0 +1,25 @@
+// { dg-options "-O -fomit-frame-pointer -fno-optimize-sibling-calls" }
+// { dg-final { check-function-bodies "**" "" } }
+
+#include <arm_sme.h>
+
+void callee_ns();
+__arm_streaming __arm_inout("za") void callee_s();
+
+/*
+** foo:
+**	...
+**	smstart	za
+**	...
+**	msr	tpidr2_el0, x\d+
+**	...
+*/
+__arm_locally_streaming __arm_new("za") const float * foo(const float* x) {
+    callee_ns ();
+    const float32_t *x_f_in = x;
+    svzero_za();
+    callee_s ();
+    return x_f_in;
+}
+
+