From: Spencer Abson <spencer.abson@arm.com>
Date: Thu, 31 Jul 2025 14:07:31 +0000 (+0000)
Subject: aarch64: Prevent streaming-compatible code from assembler rejection [PR121028]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b3da1801bef08c75f69f4376ffa05f1de2591ca8;p=thirdparty%2Fgcc.git

aarch64: Prevent streaming-compatible code from assembler rejection [PR121028]

Streaming-compatible functions can be compiled without SME enabled, but need
to use "SMSTART SM" and "SMSTOP SM" to temporarily switch into the streaming
state of a callee.  These switches are conditional on the current mode being
opposite to the target mode, so no SME instructions are executed if SME is not
available.

However, in GAS, "SMSTART SM" and "SMSTOP SM" always require +sme.  A call
from a streaming-compatible function, compiled without SME enabled, to a non
-streaming function will be rejected as:

Error: selected processor does not support `smstop sm'..

To work around this, we make use of the .inst directive to insert the literal
encodings of "SMSTART SM" and "SMSTOP SM".

gcc/ChangeLog:
	PR target/121028
	* config/aarch64/aarch64-sme.md (aarch64_smstart_sm): Use the .inst
	directive if !TARGET_SME.
	(aarch64_smstop_sm): Likewise.

gcc/testsuite/ChangeLog:
	PR target/121028
	* gcc.target/aarch64/sme/call_sm_switch_1.c: Tell check-function
	-bodies not to ignore .inst directives, and replace the test for
	"smstart sm" with one for it's encoding.
	* gcc.target/aarch64/sme/call_sm_switch_11.c: Likewise.
	* gcc.target/aarch64/sme/pr121028.c: New test.

(cherry picked from commit d52e9ef98bb30872482a46e7a2ec6a20c3ca4a4c)
---

diff --git a/gcc/config/aarch64/aarch64-sme.md b/gcc/config/aarch64/aarch64-sme.md
index f7958c90eae..3673941ab86 100644
--- a/gcc/config/aarch64/aarch64-sme.md
+++ b/gcc/config/aarch64/aarch64-sme.md
@@ -61,6 +61,10 @@
 ;; (b) they are sometimes used conditionally, particularly in streaming-
 ;; compatible code.
 ;;
+;; To prevent the latter from upsetting the assembler, we emit the literal
+;; encodings of "SMSTART SM" and "SMSTOP SM" when compiling without
+;; TARGET_SME.
+;;
 ;; =========================================================================
 
 ;; -------------------------------------------------------------------------
@@ -160,7 +164,9 @@
    (clobber (reg:VNx16BI P14_REGNUM))
    (clobber (reg:VNx16BI P15_REGNUM))]
   ""
-  "smstart\tsm"
+  {
+    return TARGET_SME ? "smstart\tsm" : ".inst 0xd503437f // smstart sm";
+  }
 )
 
 ;; Turn off streaming mode.  This clobbers all SVE state.
@@ -195,7 +201,9 @@
    (clobber (reg:VNx16BI P14_REGNUM))
    (clobber (reg:VNx16BI P15_REGNUM))]
   ""
-  "smstop\tsm"
+  {
+    return TARGET_SME ? "smstop\tsm" : ".inst 0xd503427f // smstop sm";
+  }
 )
 
 ;; -------------------------------------------------------------------------
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
index 98922aaeae0..3a63da7439c 100644
--- a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
@@ -1,5 +1,5 @@
 // { dg-options "-O -fomit-frame-pointer -fno-optimize-sibling-calls -funwind-tables" }
-// { dg-final { check-function-bodies "**" "" } }
+// { dg-final { check-function-bodies "**" "" "" { target "*-*-*" } {\t\.inst} } }
 
 void ns_callee ();
  void s_callee () [[arm::streaming]];
@@ -218,7 +218,7 @@ sc_caller_x1 (int *ptr, int a) [[arm::streaming_compatible]]
 **	bl	ns_callee_stack
 **	ldr	x16, \[x29, #?16\]
 **	tbz	x16, 0, .*
-**	smstart	sm
+**	.inst 0xd503437f // smstart sm
 **	...
 */
 void
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
index ee6f98737d9..c72d03f33b9 100644
--- a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
+++ b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
@@ -1,5 +1,6 @@
 // { dg-options "-O -fomit-frame-pointer -fno-optimize-sibling-calls -funwind-tables -mtrack-speculation" }
-// { dg-final { check-function-bodies "**" "" } }
+// { dg-final { check-function-bodies "**" "" "" { target "*-*-*" } {\t\.inst} } }
+
 
 void ns_callee ();
  void s_callee () [[arm::streaming]];
@@ -196,7 +197,7 @@ sc_caller_x1 (int *ptr, int a) [[arm::streaming_compatible]]
 **	tst	x16, #?1
 **	beq	[^\n]*
 **	csel	x15, x15, xzr, ne
-**	smstart	sm
+**	.inst 0xd503437f // smstart sm
 **	...
 */
 void
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/pr121028.c b/gcc/testsuite/gcc.target/aarch64/sme/pr121028.c
new file mode 100644
index 00000000000..a6aa11900f2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sme/pr121028.c
@@ -0,0 +1,46 @@
+// PR121028
+// { dg-do assemble { target aarch64_asm_sme_ok } }
+// { dg-options "-O --save-temps" }
+// { dg-final { check-function-bodies "**" "" "" { target "*-*-*" } {\t\.inst} } }
+
+void ns_callee ();
+
+/*
+** sc_caller_sme:
+**	...
+**	mrs	x16, svcr
+**	str	x16, \[x29, #?16\]
+**	ldr	x16, \[x29, #?16\]
+**	tbz	x16, 0, .*
+**	smstop	sm
+**	bl	ns_callee
+**	ldr	x16, \[x29, #?16\]
+**	tbz	x16, 0, .*
+**	smstart	sm
+**	...
+*/
+void sc_caller_sme() __arm_streaming_compatible
+{
+    ns_callee ();
+}
+
+#pragma GCC target "+nosme"
+
+/*
+** sc_caller_nosme:
+**	...
+**	bl	__arm_sme_state
+**	str	x0, \[x29, #?16\]
+**	ldr	x16, \[x29, #?16\]
+**	tbz	x16, 0, .*
+**	.inst 0xd503427f // smstop sm
+**	bl	ns_callee
+**	ldr	x16, \[x29, #?16\]
+**	tbz	x16, 0, .*
+**	.inst 0xd503437f // smstart sm
+**	...
+*/
+void sc_caller_nosme() __arm_streaming_compatible
+{
+    ns_callee ();
+}