[Bug tree-optimization/26144] with -O3 and pointer casts, gcc skips if

[devin at freeshell dot org]

------- Comment #2 from devin at freeshell dot org  2006-02-07 17:07 -------
I could reproduce it with that dated build.  And it isn't just debian but also
the buildroot gcc.  Here is the assembly produced from -O3.  Following that is
the assembly from -O2.  What seems to happen is that with -O3 foo() is
optimized out and in it's place .LC0 is stored on the stack.  Seems fine.  But
then the original value of "ptr" is used for calling printf instead of the
updated value from the stack.

        .file   "test.c"
        .section        .rodata.str1.1,"aMS",@progbits,1
.LC0:
        .string ""
        .text
        .p2align 4,,15
.globl foo
        .type   foo, @function
foo:
        pushl   %ebp
        movl    %esp, %ebp
        movl    8(%ebp), %eax
        movl    $.LC0, (%eax)
        popl    %ebp
        ret
        .size   foo, .-foo
        .section        .rodata.str1.1
.LC1:
        .string "%p"
        .text
        .p2align 4,,15
.globl main
        .type   main, @function
main:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $24, %esp
        movl    12(%ebp), %eax
        andl    $-16, %esp
        subl    $16, %esp
        movl    4(%eax), %eax
        testl   %eax, %eax
        movl    %eax, -4(%ebp)
        je      .L8
        movl    %eax, 4(%esp)
        movl    $.LC1, (%esp)
        call    printf
        xorl    %eax, %eax
        leave
        ret
        .p2align 4,,7
.L8:
        movl    $.LC0, -4(%ebp)
        movl    %eax, 4(%esp)
        movl    $.LC1, (%esp)
        call    printf
        xorl    %eax, %eax
        leave
        ret
        .size   main, .-main
        .ident  "GCC: (GNU) 4.0.3 20060128 (prerelease) (Debian 4.0.2-8)"
        .section        .note.GNU-stack,"",@progbits

############## Correct Version #########################

        .file   "test.c"
        .section        .rodata.str1.1,"aMS",@progbits,1
.LC0:
        .string ""
        .text
        .p2align 4,,15
.globl foo
        .type   foo, @function
foo:
        pushl   %ebp
        movl    %esp, %ebp
        movl    8(%ebp), %eax
        movl    $.LC0, (%eax)
        popl    %ebp
        ret
        .size   foo, .-foo
        .section        .rodata.str1.1
.LC1:
        .string "%p"
        .text
        .p2align 4,,15
.globl main
        .type   main, @function
main:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $24, %esp
        movl    12(%ebp), %eax
        andl    $-16, %esp
        subl    $16, %esp
        movl    4(%eax), %eax
        testl   %eax, %eax
        movl    %eax, -4(%ebp)
        je      .L8
        movl    -4(%ebp), %eax
        movl    $.LC1, (%esp)
        movl    %eax, 4(%esp)
        call    printf
        xorl    %eax, %eax
        leave
        ret
        .p2align 4,,7
.L8:
        leal    -4(%ebp), %eax
        movl    %eax, (%esp)
        call    foo
        movl    -4(%ebp), %eax
        movl    $.LC1, (%esp)
        movl    %eax, 4(%esp)
        call    printf
        xorl    %eax, %eax
        leave
        ret
        .size   main, .-main
        .ident  "GCC: (GNU) 4.0.3 20060128 (prerelease) (Debian 4.0.2-8)"
        .section        .note.GNU-stack,"",@progbits


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26144