https://gcc.gnu.org/g:14dd61736fee45b2a83502bafa1c969a2610dd1c
commit r16-1577-g14dd61736fee45b2a83502bafa1c969a2610dd1c
Author: Jakub Jelinek <ja...@redhat.com>
Date: Thu Jun 19 14:48:00 2025 +0200
expand: Align PARM_DECLs again to at least BITS_PER_WORD if possible
[PR120689]
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 patch keeps the gcc 15 behavior for avr, pru, m68k and cris (at
least some options for those) and restores the behavior before r10-577 on
other targets.
The change on the testcase on x86_64 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
2025-06-19 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.
Diff:
---
gcc/function.cc | 2 +-
gcc/testsuite/gcc.target/i386/pr120689.c | 17 +++++++++++++++++
2 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/gcc/function.cc b/gcc/function.cc
index a5b245a98e91..a3a74b44b916 100644
--- a/gcc/function.cc
+++ b/gcc/function.cc
@@ -2937,7 +2937,7 @@ assign_parm_setup_block (struct assign_parm_data_all *all,
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);
diff --git a/gcc/testsuite/gcc.target/i386/pr120689.c
b/gcc/testsuite/gcc.target/i386/pr120689.c
new file mode 100644
index 000000000000..cd10cdb487df
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr120689.c
@@ -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);
+}
