Hi!
The following testcase shows a regression caused by the r10-577 change
made for cris. Before that change, the MEM holding (in this case 3 byte)
struct parameter was BITS_PER_WORD aligned, now it is just BITS_PER_UNIT
aligned and that causes significantly worse generated code.
So, the MAX (DECL_ALIGN (parm), BITS_PER_WORD) extra alignment clearly
doesn't help just STRICT_ALIGNMENT targets, but other targets as well.
Of course, it isn't worth doing stack realignment in the rare case of
MAX_SUPPORTED_STACK_ALIGNMENT < BITS_PER_WORD targets like cris, so the
patch only bumps the alignment if it won't go the
> MAX_SUPPORTED_STACK_ALIGNMENT path because of that optimization.
The change on the testcase is:
bar:
- movl %edi, %eax
- movzbl %dil, %r8d
- movl %esi, %ecx
- movzbl %sil, %r10d
- movl %edx, %r9d
- movzbl %dl, %r11d
- shrl $16, %edi
- andl $65280, %ecx
- shrl $16, %esi
- shrl $16, %edx
- andl $65280, %r9d
- orq %r10, %rcx
- movzbl %dl, %edx
- movzbl %sil, %esi
- andl $65280, %eax
- movzbl %dil, %edi
- salq $16, %rdx
- orq %r11, %r9
- salq $16, %rsi
- orq %r8, %rax
- salq $16, %rdi
- orq %r9, %rdx
- orq %rcx, %rsi
- orq %rax, %rdi
jmp foo
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-06-18 Jakub Jelinek <ja...@redhat.com>
PR target/120689
* function.cc (assign_parm_setup_block): Align parm to at least
word alignment even on !STRICT_ALIGNMENT targets, as long as
BITS_PER_WORD is not larger than MAX_SUPPORTED_STACK_ALIGNMENT.
* gcc.target/i386/pr120689.c: New test.
--- gcc/function.cc.jj 2025-05-20 08:14:06.105410349 +0200
+++ gcc/function.cc 2025-06-18 10:25:53.841280559 +0200
@@ -2937,7 +2937,7 @@ assign_parm_setup_block (struct assign_p
if (stack_parm == 0)
{
HOST_WIDE_INT parm_align
- = (STRICT_ALIGNMENT
+ = ((STRICT_ALIGNMENT || BITS_PER_WORD <= MAX_SUPPORTED_STACK_ALIGNMENT)
? MAX (DECL_ALIGN (parm), BITS_PER_WORD) : DECL_ALIGN (parm));
SET_DECL_ALIGN (parm, parm_align);
--- gcc/testsuite/gcc.target/i386/pr120689.c.jj 2025-06-18 10:29:39.744346367
+0200
+++ gcc/testsuite/gcc.target/i386/pr120689.c 2025-06-18 10:33:53.504111156
+0200
@@ -0,0 +1,17 @@
+/* PR target/120689 */
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -mtune=generic -fno-stack-protector -masm=att" } */
+/* { dg-final { scan-assembler-not "\t\(movzbl\|shrl\|salq\|orq\)\t" } } */
+
+struct S { char a, b, c; };
+
+[[gnu::noipa]]
+void foo (struct S x, struct S y, struct S z)
+{
+}
+
+void
+bar (struct S x, struct S y, struct S z)
+{
+ [[gnu::musttail]] return foo (x, y, z);
+}
Jakub
