[Bug optimization/11601] New: if-conversion2 gets rid of branch and return when used with builtins

["pinskia at physics dot uc dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11601

           Summary: if-conversion2 gets rid of branch and return when used
                    with builtins
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: critical
          Priority: P1
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at physics dot uc dot edu
                CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: powerpc-*-*

Compile the following code with -O and -maltivec:
void prefetch (void *p, int s)
{
  if (s)
    __builtin_prefetch (p, 1, 1);
}

void t(void *p, int s)
{
  if (s)
    __builtin_altivec_dst (p, 0, 0);
}
resulting asm:
_prefetch:
        dcbtst 0,r3
        blr
_t:
        li r0,0
        dst r3,r0,0
        blr
But compiling:
void g(int *p, int s)
{
  if (s)
    *p=0;
}
results in correct code:
_g:
        cmpwi cr7,r4,0
        beqlr- cr7             <--- branch on equal (cr7eq set) to link reg (aka return).
        li r0,0
        stw r0,0(r3)
        blr