[Bug c/112507] New: Missed optimization of strcpy(3) (or stpcpy(3)) with previous strnlen(3)

[Bug c/112507] New: Missed optimization of strcpy(3) (or stpcpy(3)) with previous strnlen(3)

[alx at kernel dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112507

            Bug ID: 112507
           Summary: Missed optimization of strcpy(3) (or stpcpy(3)) with
                    previous strnlen(3)
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alx at kernel dot org
  Target Milestone: ---

The following code can be optimized to use memcpy(3), since the length
of the copy is known (we've just called strnlen(3), and discarded the
possibility of truncated lengths).

$ cat strxcpy.c
#include <stddef.h>
#include <string.h>
#include <sys/types.h>

ssize_t
strxcpy(char *restrict dst, const char *restrict src, size_t dsize)
{
        if (strnlen(src, dsize) == dsize)
                return -1;

        return stpcpy(dst, src) - dst;
}


This compiles to stpcpy(3).  Similar code written with strcpy(3) also
keeps strcpy(3).  But they could be optimized with mempcpy(3) or
memcpy(3).


On Mon, Nov 13, 2023 at 07:56:00AM +0100, Richard Biener wrote:                 
> It looks like a transform for the strlen pass.

[Bug tree-optimization/112507] Missed optimization of strcpy(3) (or stpcpy(3)) with previous strnlen(3)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112507

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement