[Bug rtl-optimization/31313] New: consecutive strcmps are not merged

[tobi at gcc dot gnu dot org]

I just ran into some code which did something like

int strcmp(const char *, const char *);

int f (const char *c)
{
  return (strcmp (c, "aaa") == 0 || strcmp (c, "aab") == 0);
}

It would be possible to optimize this into something like (hopefully I get it
right)
int f (const char *c)
{
  if (strncmp (c, "aa", 2))
    return 0;
  return ((c[2] == 'a' || c[2] == 'b') && !c[3]);
}

Instead, we scan through the whole string twice, as can be seen in the
assembly.

Likewise, more complicated combinations of comparisons could be reduced into an
optimal matching sequence.  Putting this into component rtl-optimization,
because the strcmp calls survive all of the tree optimizers unchanged.


-- 
           Summary: consecutive strcmps are not merged
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tobi at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31313