[Bug middle-end/24729] New: function calls created by builtins do not make use of inline definitions

["ghazi at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

When doing transformations on builtins, if the builtin results in a function
call that has an inline expansion, GCC emits a library call not the inline
function body.  E.g. glibc defines an inline for fputc_unlocked.  Given this
code:

#define _GNU_SOURCE
#include <stdio.h>
#define MAX 100000000

int main ()
{
  int i;
  for (i=0; i<MAX; i++)
  {
#ifdef FPUTC_DIRECT
    fputc_unlocked('1', stdout);
#else
    fputs_unlocked("1", stdout);
#endif
  }
  return 0;
}


If you compile it on a glibc box (I used x86_64-unknown-linux-gnu) with -O2 and
look at the assembly the fputs_unlocked gets turned into fputc_unlocked as
expected due to a strlen of 1 in the parameter, but nothing is further
optimized.  However if you use -DFPUTC_DIRECT, you should see that GCC inserts
the inline definition of fputc_unlocked and this version of the code runs about
10x faster than the library call to fputc_unlocked.

When expanding function calls created by builtin substitution, GCC should check
if that identifier refers to an inline function and substitute that definition
if possible.


-- 
           Summary: function calls created by builtins do not make use of
                    inline definitions
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ghazi at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24729