[Bug middle-end/124697] Unnecessary stack realignment

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124697

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to H.J. Lu from comment #3)
> [hjl@gnu-tgl-3 pr124697]$ cat foo.c
> typedef double v4df __attribute__((vector_size(32)));
> typedef double v2df __attribute__((vector_size(16)));
> typedef struct {
>   v2df a[2];
> } c __attribute__((aligned(32)));
> extern v4df d;
> void
> e (float a1, float a2, float a3, float a4, float a5, float a6, c f)
> {
>   d = *(v4df *) &f;
> }
> [hjl@gnu-tgl-3 pr124697]$ make foo.s
> /export/build/gnu/tools-build/gcc-gitlab-debug/build-x86_64-linux/gcc/xgcc
> -B/export/build/gnu/tools-build/gcc-gitlab-debug/build-x86_64-linux/gcc/ -O2
> -march=x86-64-v4 -S foo.c
> [hjl@gnu-tgl-3 pr124697]$ cat foo.s
> 	.file	"foo.c"
> 	.text
> 	.p2align 4
> 	.globl	e
> 	.type	e, @function
> e:
> .LFB0:
> 	.cfi_startproc
> 	pushq	%rbp
> 	.cfi_def_cfa_offset 16
> 	.cfi_offset 6, -16
> 	movq	%rsp, %rbp
> 	.cfi_def_cfa_register 6
> 	vmovapd	16(%rbp), %ymm0  <<<<<<< f is aligned at 16 bytes.

Yes.  This is wrong code.  My patch would have fixed it, doing
effectively (but restricted to x86 at this point)

diff --git a/gcc/function.cc b/gcc/function.cc
index 46c0d8b54c2..d44815afc16 100644
--- a/gcc/function.cc
+++ b/gcc/function.cc
@@ -2840,7 +2840,7 @@ assign_parm_adjust_stack_rtl (tree parm, struct
assign_parm_data_one *data)
                                                 MEM_ALIGN (stack_parm))))
          || (data->nominal_type
              && TYPE_ALIGN (data->nominal_type) > MEM_ALIGN (stack_parm)
-             && (MEM_ALIGN (stack_parm) < PREFERRED_STACK_BOUNDARY
+             && (MEM_ALIGN (stack_parm) < BIGGEST_ALIGNMENT 
                  /* If its address is taken, make a local copy whose
                     maximum alignment is MAX_SUPPORTED_STACK_ALIGNMENT.
                   */


> 	vmovapd	%ymm0, d(%rip)
> 	vzeroupper
> 	popq	%rbp
> 	.cfi_def_cfa 7, 8
> 	ret
> 	.cfi_endproc
> .LFE0:
> 	.size	e, .-e
> 	.ident	"GCC: (GNU) 16.0.1 20260331 (experimental)"
> 	.section	.note.GNU-stack,"",@progbits
> [hjl@gnu-tgl-3 pr124697]$