[Bug tree-optimization/95821] New: Failure to optimize strchr to use memchr for string constant

[Bug tree-optimization/95821] New: Failure to optimize strchr to use memchr for string constant

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821

            Bug ID: 95821
           Summary: Failure to optimize strchr to use memchr for string
                    constant
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

auto f(char c)
{
    return strchr("123", c);
}

This can be optimized to `return memchr("123", c, 4)`. This transformation is
done by LLVM, but not by GCC.

[Bug tree-optimization/95821] Failure to optimize strchr to use memchr for string constant

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For -Os that is an undesirable change because it makes the code larger.  But
otherwise yes, seems useful.

[Bug tree-optimization/95821] Failure to optimize strchr to use memchr for string constant

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Severity|normal                      |enhancement
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-12-22

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
Though for small strings it might even make sense to inline it, eg.:
auto f(char c)
{
    return strchr("123", c);
}
to
auto f(char c)
{
  auto t = "123";
  int t1;
  switch (c)
    {
       case '1':
         t1 = 1;
       case '2':
         t1 = 2;
       case '3':
         t1 = 3;
       default:
         t = 0;
         return t;
    }
   return t+t1;
}

[Bug tree-optimization/95821] Failure to optimize strchr to use memchr for string constant

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Confirmed.
> auto f(char c)
> {
>   auto t = "123";
>   int t1;
>   switch (c)
>     {
>        case '1':
>          t1 = 1;
>        case '2':
>          t1 = 2;
>        case '3':
>          t1 = 3;
>        default:
>          t = 0;
>          return t;
>     }
>    return t+t1;
> }

I missed '\0' (and break's):

auto f(char c)
{
  auto t = "123";
  int t1;
  switch (c)
    {
       case '1':
         t1 = 1;
         break;
       case '2':
         t1 = 2;
         break;
       case '3':
         t1 = 3;
         break;
       case '\0':
         t1 = 4;
         break;
       default:
         t = 0;
         return t;
    }
   return t+t1;
}

[Bug tree-optimization/95821] Failure to optimize strchr to use memchr for string constant

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95821

--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 53157
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53157&action=edit
A patch