Re: [PATCH] Optimize var = STRING_CST

["Richard Guenther" <richard.guenther@gmail.com>]

On 8/23/07, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> The following patch optimizes initialization of an array from a STRING_CST.
> Without this patch store_expr will always force the STRING_CST into memory
> and then do a block move from there, followed by optional clear_storage
> if the STRING_CST is shorter than the array.  This patch uses
> store_by_pieces if possible.
> With the patch:
> struct A { char c[10]; };
>
> void
> foo (void)
> {
>   struct A a = { "abcdefghi" };
>   baz (&a);
> }
>
> void
> bar (void)
> {
>   struct A a;
>   __builtin_strcpy (&a.c[0], "abcdefghi");
>   baz (&a);
> }
> both routines are the same on x86_64 except for
> slightly different register allocation, without that patch
> for foo a .LC0 constant with the string literal is emitted and foo
> copies over from that string into a.c array.
>
> Tested on x86_64-linux, ok for trunk?

This is ok if you add a testcase.  I also bet we have a PR  somewhere
for this one...

Thanks,
Richard.

> 2007-08-23  Jakub Jelinek  <jakub@redhat.com>
>
>         * expr.c (store_expr): Optimize initialization of an array
>         with STRING_CST.
>         * expr.h (builtin_strncpy_read_str): New prototype.
>         * builtins.c (builtin_strncpy_read_str): Remove prototype.
>         No longer static.