aarch64: Stack-clash prologues and VG saves [PR113995]

This patch fixes an ICE for a combination of:

- -fstack-clash-protection
- a frame that has SVE save slots
- a frame that has no GPR save slots
- a frame that has a VG save slot

The allocation code was folding the SVE save slot allocation into
the initial frame allocation, so that we had one allocation of
size <size of SVE registers> + 16.  But the VG save code itself
expected the allocations to remain separate, since it wants to
store at a constant offset from SP or FP.

The VG save isn't shrink-wrapped and so acts as a probe of the
initial allocations.  It should therefore be safe to keep separate
allocations in this case.

The scans in locally_streaming_1.c expect no stack clash protection,
so the patch forces that and adds a separate compile-only test for
when protection is enabled.

gcc/
	PR target/113995
	* config/aarch64/aarch64.cc (aarch64_expand_prologue): Don't
	fold the SVE allocation into the initial allocation if the
	initial allocation includes a VG save.

gcc/testsuite/
	PR target/113995
	* gcc.target/aarch64/sme/locally_streaming_1.c: Require
	-fno-stack-clash-protection.
	* gcc.target/aarch64/sme/locally_streaming_1_scp.c: New test.

3 files changed, 11 insertions, 3 deletions

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 104f7e1..6a39ed8 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -9523,7 +9523,9 @@ aarch64_expand_prologue (void)
   if (aarch64_cfun_enables_pstate_sm ())
     force_isa_mode = AARCH64_FL_SM_ON;
 
-  if (flag_stack_clash_protection && known_eq (callee_adjust, 0))
+  if (flag_stack_clash_protection
+      && known_eq (callee_adjust, 0)
+      && known_lt (frame.reg_offset[VG_REGNUM], 0))
     {
       /* Fold the SVE allocation into the initial allocation.
 	 We don't do this in aarch64_layout_arg to avoid pessimizing
@@ -9651,7 +9653,10 @@ aarch64_expand_prologue (void)
   if (maybe_ne (sve_callee_adjust, 0))
     {
       gcc_assert (!flag_stack_clash_protection
-		  || known_eq (initial_adjust, 0));
+		  || known_eq (initial_adjust, 0)
+		  /* The VG save isn't shrink-wrapped and so serves as
+		     a probe of the initial allocation.  */
+		  || known_eq (frame.reg_offset[VG_REGNUM], bytes_below_sp));
       aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx,
 					      sve_callee_adjust,
 					      force_isa_mode,
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1.c b/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1.c
index 4bb637f..cb235f5 100644
--- a/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1.c
@@ -1,4 +1,4 @@
-// { dg-options "-O -fomit-frame-pointer" }
+// { dg-options "-O -fomit-frame-pointer -fno-stack-clash-protection" }
 // { dg-final { check-function-bodies "**" "" } }
 
 void consume_za () [[arm::streaming, arm::inout("za")]];
diff --git a/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1_scp.c b/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1_scp.c
new file mode 100644
index 0000000..6b7f47d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sme/locally_streaming_1_scp.c
@@ -0,0 +1,3 @@
+// { dg-options "-O -fomit-frame-pointer -fstack-clash-protection" }
+
+#include "locally_streaming_1.c"