[Bug target/28946] [4.0/4.1/4.2 Regression] assembler shifts set the flag ZF, no need to re-test to zero

[uros at kss-loka dot si]

------- Comment #7 from uros at kss-loka dot si  2006-09-05 13:43 -------
Hm, proposed patch now generates worse code for following test:

extern int fnc1(void);
extern int fnc2(void);

int test(int x)
{
        if (x & 0x02)
         return fnc1();
        else if (x & 0x01)
         return fnc2();
        else
         return 0;
}

It generates:

test:
        movl 4(%esp), %edx
        movl %edx, %eax
        andl $2, %eax
        jne .L10
        andl $1, %edx
        jne .L11
        xorl %eax, %eax
        ret
        .p2align 4,,7
.L11:
        .p2align 4,,8
        jmp fnc2
        .p2align 4,,7
.L10:
        .p2align 4,,7
        jmp fnc1

due to marking %eax live in first comparison, "and" is used instead of "test",
and a regmove is emitted before comparison. Ideally gcc should generate:

test:
        movl 4(%esp), %eax
        testl  $2, %eax
        jne .L6
        andl $1, %eax
        jne .L7
        xorl %eax, %eax
        ret
        .p2align 2,,3
.L7:
        jmp fnc2
        .p2align 2,,3
.L6:
        jmp fnc1


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28946