i386: Require just 32-bit alignment for SLOT_FLOATxFDI_387 -m32 -mpreferred-stack-boundary=2 DImode temporaries [PR109276]

The following testcase ICEs since r11-2259 because assign_386_stack_local
-> assign_stack_local -> ix86_local_alignment now uses 64-bit alignment
for DImode temporaries rather than 32-bit as before.
Most of the spots in the backend which ask for DImode temporaries are during
expansion and those apparently are handled fine with -m32
-mpreferred-stack-boundary=2, we dynamically realign the stack in that case
(most of the spots actually don't need that alignment but at least one
does), then 2 spots are in STV which I assume also work correctly.
But during splitting we can create a DImode slot which doesn't need to be
64-bit alignment (it is nicer for performance though), when we apparently
aren't able to detect it for dynamic stack realignment purposes.

The following patch just makes the slot 32-bit aligned in that rare case.

2023-03-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/109276
	* config/i386/i386.cc (assign_386_stack_local): For DImode
	with SLOT_FLOATxFDI_387 and -m32 -mpreferred-stack-boundary=2 pass
	align 32 rather than 0 to assign_stack_local.

	* gcc.target/i386/pr109276.c: New test.

(cherry picked from commit 4b5ef857f5faf09f274c0a95c67faaa80d198124)

1 files changed, 13 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.target/i386/pr109276.c b/gcc/testsuite/gcc.target/i386/pr109276.c
new file mode 100644
index 0000000..5d0827a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr109276.c
@@ -0,0 +1,13 @@
+/* PR target/109276 */
+/* { dg-do compile } */
+/* { dg-options "-march=x86-64" } */
+/* { dg-additional-options "-mpreferred-stack-boundary=2" { target ia32 } } */
+
+long long a;
+long double b;
+
+void
+foo (void)
+{
+  b += a;
+}