From: Alice Carlotti <alice.carlotti@arm.com>
Date: Wed, 14 Jan 2026 13:48:35 +0000 (+0000)
Subject: aarch64: Disable shrink-wrap for locally-streaming functions [PR 123624]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1ced019ad9de965971d6fafe0d6fa4af2ddf54ac;p=thirdparty%2Fgcc.git

aarch64: Disable shrink-wrap for locally-streaming functions [PR 123624]

The meaning of poly_int values changes depending on whether we are in
streaming or non-streaming mode, but this dependency is not explicitly
tracked.  Locally-streaming functions can change streaming state in the
prologue and epilogue, so it is unsafe to apply shrink wrapping to these
functions, as doing so could change the mode seen by instructions like
cntd.

gcc/ChangeLog:

	PR target/123624
	* config/aarch64/aarch64-protos.h
	(aarch64_use_simple_return_insn_p): New.
	* config/aarch64/aarch64.cc
	(aarch64_use_simple_return_insn_p): New, used...
	* config/aarch64/aarch64.md (simple_return): ...here.

gcc/testsuite/ChangeLog:

	PR target/123624
	* gcc.target/aarch64/sme/sme-shrinkwrap.c: New test.
---

diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index 48d3a3de235..d1f2873f208 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -984,6 +984,7 @@ bool aarch64_uimm12_shift (unsigned HOST_WIDE_INT);
 int aarch64_movk_shift (const wide_int_ref &, const wide_int_ref &);
 bool aarch64_is_mov_xn_imm (unsigned HOST_WIDE_INT);
 bool aarch64_use_return_insn_p (void);
+bool aarch64_use_simple_return_insn_p (void);
 const char *aarch64_output_casesi (rtx *);
 const char *aarch64_output_load_tp (rtx);
 const char *aarch64_output_sme_zero_za (rtx);
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 57aa83de3fb..00e619f26c5 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -10794,6 +10794,20 @@ aarch64_use_return_insn_p (void)
   return known_eq (cfun->machine->frame.frame_size, 0);
 }
 
+/* Return false for locally streaming functions in order to avoid
+   shrink-wrapping them.  Shrink-wrapping is unsafe when the function prologue
+   and epilogue contain streaming state change, because these implicitly change
+   the meaning of poly_int values.  */
+
+bool
+aarch64_use_simple_return_insn_p (void)
+{
+  if (aarch64_cfun_enables_pstate_sm ())
+    return false;
+
+  return true;
+}
+
 /* Generate the epilogue instructions for returning from a function.
    This is almost exactly the reverse of the prolog sequence, except
    that we need to insert barriers to avoid scheduling loads that read
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 70a64a6c0ed..e44b1cd9eef 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -1435,7 +1435,7 @@
 
 (define_insn "simple_return"
   [(simple_return)]
-  ""
+  "aarch64_use_simple_return_insn_p ()"
   {
     output_asm_insn ("ret", operands);
     return aarch64_sls_barrier (aarch64_harden_sls_retbr_p ());
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/sme-shrinkwrap.c b/gcc/testsuite/gcc.target/aarch64/sme/sme-shrinkwrap.c
new file mode 100644
index 00000000000..b8dfd5f92f6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sme/sme-shrinkwrap.c
@@ -0,0 +1,78 @@
+/* { dg-options "-O3 -fshrink-wrap" } */
+/* { dg-do run { target { aarch64_sme_hw && aarch64_sve_hw } } } */
+/* { dg-do compile { target { ! { aarch64_sme_hw && aarch64_sve_hw } } } } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+#include <arm_sme.h>
+
+#pragma GCC target "+sve"
+
+[[gnu::noipa]]
+__arm_streaming
+int callee (int x)
+{
+  return 0;
+}
+
+/*
+** foo:
+**	cbnz	w0, [^\n]*
+**	cntd	x0
+**	ret
+**	...
+*/
+__arm_streaming
+int foo(int x)
+{
+    if (x)
+        return callee(3);
+    return svcntd();
+}
+
+/*
+** bar:
+**	...
+**	smstart	[^\n]*
+**	...
+** (
+**	cntd	[^\n]*
+**	...
+**	cbn?z	[^\n]*
+** |
+**	cbn?z	[^\n]*
+**	...
+**	cntd	[^\n]*
+** )
+**	...
+*/
+
+__arm_locally_streaming
+int bar(int x)
+{
+    if (x)
+        return callee(3);
+    return svcntd();
+}
+
+/*
+** baz:
+**	cbnz	w0, [^\n]*
+**	cntd	x0
+**	ret
+**	...
+*/
+__arm_streaming
+int baz(int x)
+{
+    if (x)
+        return callee(3);
+    return svcntd();
+}
+
+[[gnu::noipa]]
+int main()
+{
+  if (bar(0) != svcntsd())
+    __builtin_abort();
+  return 0;
+}