[Bug tree-optimization/61056] New: strchr (x, 0) is not converted to strlen (x)

[Bug tree-optimization/61056] New: strchr (x, 0) is not converted to strlen (x)

[olegendo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61056

            Bug ID: 61056
           Summary: strchr (x, 0) is not converted to strlen (x)
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
            Target: sh*-*-*

At least on SH and r210026 the following:

extern "C" const char* strchr (const char*,int);

const char* test (const char* x)
{
  return strrchr (x, 0);
}

does not get converted to a strlen (x).  It seems that tree-ssa-strlen is
trying to do something but always fails.

[Bug tree-optimization/61056] strchr (x, 0) is not converted to strlen (x)

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61056

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> ---
1) your testcase uses strrchr rather than strchr
2) why do you think it is desirable to convert strchr (x, 0) to x + strlen (x)?
Unless you have good library implementation for the latter and bad for the
former, strchr (x, 0) should be a win.
What the strlen pass does is that if you e.g. use strchr (x, 0) or strlen (x)
several times when the lengths of the strings actually can't change in between,
it can avoid the second and following call.  And, it is able to deal even with
strlen (x) used in one place and strchr (x, 0) in another or vice versa etc.
(plus various other optimizations).

[Bug tree-optimization/61056] strchr (x, 0) is not converted to strlen (x)

[olegendo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61056

--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> 1) your testcase uses strrchr rather than strchr

Sorry, typo/pasto.  It was meant to be "strchr".

> 2) why do you think it is desirable to convert strchr (x, 0) to x + strlen
> (x)?

On SH we have a builtin strlen implementation.  I was just expecting strchr (x,
0) to utilize it, that's all.

> Unless you have good library implementation for the latter and bad for the
> former, strchr (x, 0) should be a win.
> What the strlen pass does is that if you e.g. use strchr (x, 0) or strlen
> (x) several times when the lengths of the strings actually can't change in
> between, it can avoid the second and following call.  And, it is able to
> deal even with strlen (x) used in one place and strchr (x, 0) in another or
> vice versa etc. (plus various other optimizations).

Ah, thanks for the explanation.
BTW, are there any plans to add true builtin strchr support so that it can be
expanded by the target code in the same way as strlen?