[Bug tree-optimization/103799] New: switch expansion could be smarter

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103799

            Bug ID: 103799
           Summary: switch expansion could be smarter
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
auto f(char c)
{
  int t1;
  switch (c)
    {
       case '1':
         t1 = 1;
         break;
       case '2':
         t1 = 2;
         break;
       case '3':
         t1 = 3;
         break;
       case '\0':
         t1 = 4;
         break;
       default:
         t1 = -1;
    }
   return t1;
}


auto f1(char c)
{
  int t1;
  switch (c)
    {
       case '1':
         t1 = 1;
         break;
       case '2':
         t1 = 2;
         break;
       case '3':
         t1 = 3;
         break;
    default:
      if (c == '\0') t1 = 4; else t1 = -1;
    }
   return t1;
}

f1 produces better code than f.