"H.J. Lu" <hjl.to...@gmail.com> writes:
> Since a backend may ignore user type alignment for arguments passed on
> stack, update alignment for arguments passed on stack when copying MEM's
> memory attributes.
>
> gcc/
>
> PR target/120839
> * emit-rtl.cc (set_mem_attrs): Update alignment for argument on
> stack.
>
> gcc/testsuite/
>
> PR target/120839
> * gcc.target/i386/pr120839-1.c: New test.
> * gcc.target/i386/pr120839-2.c: Likewise.
>
>
> --
> H.J.
>
> From 3f8a9bfb4beae47bfc0da20b517a5b3b06a1cbcc Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.to...@gmail.com>
> Date: Sat, 28 Jun 2025 06:27:25 +0800
> Subject: [PATCH] Update alignment for argument on stack
>
> Since a backend may ignore user type alignment for arguments passed on
> stack, update alignment for arguments passed on stack when copying MEM's
> memory attributes.
>
> gcc/
>
> PR target/120839
> * emit-rtl.cc (set_mem_attrs): Update alignment for argument on
> stack.
>
> gcc/testsuite/
>
> PR target/120839
> * gcc.target/i386/pr120839-1.c: New test.
> * gcc.target/i386/pr120839-2.c: Likewise.
>
> Signed-off-by: H.J. Lu <hjl.to...@gmail.com>
> ---
> gcc/emit-rtl.cc | 14 ++++++++++++++
> gcc/testsuite/gcc.target/i386/pr120839-1.c | 14 ++++++++++++++
> gcc/testsuite/gcc.target/i386/pr120839-2.c | 19 +++++++++++++++++++
> 3 files changed, 47 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/i386/pr120839-1.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr120839-2.c
>
> diff --git a/gcc/emit-rtl.cc b/gcc/emit-rtl.cc
> index f4fc92bb37a..0d1616361ca 100644
> --- a/gcc/emit-rtl.cc
> +++ b/gcc/emit-rtl.cc
> @@ -389,6 +389,20 @@ set_mem_attrs (rtx mem, mem_attrs *attrs)
> {
> MEM_ATTRS (mem) = ggc_alloc<mem_attrs> ();
> memcpy (MEM_ATTRS (mem), attrs, sizeof (mem_attrs));
> + if (MEM_EXPR (mem))
> + {
> + tree base_address = get_base_address (MEM_EXPR (mem));
> + if (base_address && TREE_CODE (base_address) == PARM_DECL)
> + {
> + /* User alignment on type may be ignored for parameter
> + passed on stack. */
> + tree type = TREE_TYPE (base_address);
> + unsigned int alignment
> + = targetm.calls.function_arg_boundary (TYPE_MODE (type),
> + type);
> + set_mem_align (mem, alignment);
> + }
> + }
> }
> }
This doesn't feel like the right place to address this. set_mem_attrs
is just supposed to install the attributes that it has been given,
without second-guessing the contents.
Where does the incorrect alignment ultimately come from? (As in,
which piece of code creates the MEM and fails to give it the correct
alignment?)
Richard
>
> diff --git a/gcc/testsuite/gcc.target/i386/pr120839-1.c
> b/gcc/testsuite/gcc.target/i386/pr120839-1.c
> new file mode 100644
> index 00000000000..74fbf876330
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr120839-1.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +typedef struct
> +{
> + long double a;
> + long double b;
> +} c __attribute__((aligned(32)));
> +extern double d;
> +void
> +bar (c f)
> +{
> + d = f.a;
> +}
> diff --git a/gcc/testsuite/gcc.target/i386/pr120839-2.c
> b/gcc/testsuite/gcc.target/i386/pr120839-2.c
> new file mode 100644
> index 00000000000..e5b711c966f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr120839-2.c
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +/* { dg-final { scan-assembler-not "and\[lq\]?\[\\t \]*\\$-32,\[\\t
> \]*%\[re\]?sp" } } */
> +
> +typedef struct
> +{
> + long double a;
> + long double b;
> +} c __attribute__((aligned(32)));
> +extern c x;
> +extern double d;
> +extern void bar (c);
> +void
> +foo (void)
> +{
> + x.a = d;
> + x.b = d;
> + bar (x);
> +}
