[Bug tree-optimization/65412] New: missing control flow optimisation

[skvadrik at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65412

            Bug ID: 65412
           Summary: missing control flow optimisation
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: skvadrik at gmail dot com

Created attachment 35023
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35023&action=edit
files 1.c (source), 1.s (gcc assembly), 2.s (clang assembly)

Consider the following code:

void f(int x)
{
   if (x == 0) f0();
   else if (x == 1) f1();
   else if (x == 2) f2();
   else if (x == 3) f3();
   else if (x == 4) f4();
   else if (x == 5) f5();
}

gcc-4.9.2 doesn't optimize ifs to decision tree, jump table or something (see
1.s in attach). clang does (2.s in attach, jump table).

Maybe you could improve that?