[Bug middle-end/21265] New: [4.0,4.1 regression] GCC fails to optimize tail call to memset

[ghazi at gcc dot gnu dot org]

Given the code below, GCC fails to optimize the tail call to memset into a jmp 
on x86_64-unknown-linux-gnu as of 4.0 or 4.1 mainline.  Versions 3.4 and 3.3 
perform the transformation so it is a regression.  All GCC versions on x86_64 
manage to optimize the call to my_memset so it may be related to builtin 
handling.  FYI none of the above versions of gcc optimize either memset or 
my_memset on x86.  So on x86 it's consistently failing, I'm not sure if that's 
intentional or not.  But x86_64 is a regression.

Compile with -O2 -S:

#include <stddef.h>
extern void *memset (void *, int, size_t);
extern void *my_memset (void *, int, size_t);

void
foo (void *to, size_t count)
{
  memset (to, 0, count);
}

void
bar (void *to, size_t count)
{
  my_memset (to, 0, count);
}

-- 
           Summary: [4.0,4.1 regression] GCC fails to optimize tail call to
                    memset
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ghazi at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21265