[Bug c/18750] New: i386/amd64 -O1 faulty assembly code

["vlad902 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

I've found that when using -O1 on a default install FreeBSD 5.3/i386 system with
gcc 3.4.2 (default) that using -O1 causes. I've been able to reproduce on a Red
Hat Linux/amd64 system with gcc 3.3.3. Specifically I've found that on i386 a
code statement of "while(mutex);" (where mutex is a global volatile int) without
-O1 specified gcc produces:
.L4:
        cmpl    $0, mutex
        jne     .L5
        jmp     .L4
.L5:
On the other hand gcc with -O1 specified produces:
        cmpl    $0, mutex
        .p2align 2,,3
.L4:
        je      .L4
In this case the "je" instruction loops forever if mutex is initially 0 causing
unwanted behavior. I have attached a test case.

Use of higher values as arguments to -O also cause a freeze in the test case.

-- 
           Summary: i386/amd64 -O1 faulty assembly code
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: vlad902 at gmail dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-fbsdproj-freebsd
  GCC host triplet: i386-fbsdproj-freebsd
GCC target triplet: i386-fbsdproj-freebsd


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18750