[Bug tree-optimization/59639] New: Code in a cold basic block is not pushed to .text.unlikely

[avi@cloudius-systems.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59639

            Bug ID: 59639
           Summary: Code in a cold basic block is not pushed to
                    .text.unlikely
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: avi@cloudius-systems.com

Consider the code:


  [[gnu::cold]]
  int slow_path();

  int f()
  {
    asm goto ("" : : : : cold);
    return 1;
  cold:
    return slow_path();
  }

since slow_path() is cold, the compiler can infer that the basic block
beginning with the cold: label is also cold, so it should be placed in
.text.unlikely.  Yet it isn't:

0000000000000000 <_Z1fv>:
   0:   b8 01 00 00 00          mov    $0x1,%eax
   5:   c3                      retq   
   6:   e9 00 00 00 00          jmpq   b <_Z1fv+0xb>

Adding a cold attribute to the label doesn't help.

Expected results: the jmpq instruction should be placed in .text.unlikely.