[Bug target/44474] GCC inserts redundant "test" instruction due to incorrect clobber

[astrange at ithinksw dot com]

------- Comment #1 from astrange at ithinksw dot com  2010-07-01 03:43 -------
The problem is combine.

This:

int test2( int *b )
{
        int b_ = *b;
    b_--;
    if( b_ == 0 ) {
        *b = b_;
        return foo();
    }
    *b = b_;
    return 0;
}

works:
_test2:
LFB1:
        movl    (%rdi), %eax
        decl    %eax
        je      L7 <- uses decl
        movl    %eax, (%rdi)
        xorl    %eax, %eax
        ret
        .align 4,0x90
L7:
        movl    $0, (%rdi)
        xorl    %eax, %eax
        jmp     _foo

The original turns (*b)-- into load/dec/store/cmp - combine tries to combine
dec/store which fails, but doesn't try dec/cmp.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44474