[Bug tree-optimization/47815] New: Tail call regression with GCC snapshot

[adam at consulting dot net.nz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47815

           Summary: Tail call regression with GCC snapshot
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: adam@consulting.net.nz


$ gcc-snapshot.sh --version
gcc (Debian 20110126-0ubuntu1) 4.6.0 20110126 (experimental) [trunk revision
169285]

If the code below is compiled with Debian sid gcc-snapshot no tail calls are
generated:

#include <assert.h>

__attribute__((noinline)) void tail_call0() {
  assert("tail_call0"=="");
}

__attribute__((noinline)) void tail_call1() {
  assert("tail_call1"=="");
}

void make_tail_calls(int flag) {
  if (flag) tail_call0(); else tail_call1();
}

int main() {
  return 0;
}

$ gcc-snapshot.sh -Os tail_call_regression.c && objdump -d -m i386:x86-64 a.out
|less

0000000000400508 <make_tail_calls>:
  400508:       31 c0                   xor    %eax,%eax
  40050a:       85 ff                   test   %edi,%edi
  40050c:       51                      push   %rcx
  40050d:       74 05                   je     400514 <make_tail_calls+0xc>
  40050f:       e8 c0 ff ff ff          callq  4004d4 <tail_call0>
  400514:       e8 d5 ff ff ff          callq  4004ee <tail_call1>

Expected output:

$ gcc-4.5 -Os tail_call_regression.c && objdump -d -m i386:x86-64 a.out |less

000000000040052e <make_tail_calls>:
  40052e:       85 ff                   test   %edi,%edi
  400530:       74 07                   je     400539 <make_tail_calls+0xb>
  400532:       31 c0                   xor    %eax,%eax
  400534:       e9 bb ff ff ff          jmpq   4004f4 <tail_call0>
  400539:       31 c0                   xor    %eax,%eax
  40053b:       e9 d1 ff ff ff          jmpq   400511 <tail_call1>