Why can't this information be used to optimize comparisons?
My patch caused GCC to infer that x & 7 > 7 is false. But I couldn't
think of a quick way to use this to optimize away the check, because
then GCC crashed.
Does it work only for consecutive ands?
Or is it just an early constant
?
Piotr
- Original Message -
From: "Paolo Bonzini" <[EMAIL PROTECTED]>
To: "GCC Development" ; <[EMAIL PROTECTED]>; "Diego Novillo"
<[EMAIL PROTECTED]>; "Giovanni Bajo" <[EMAIL PROTECTED]>
Sent: Monday, Au
void Switch4(int x) {
switch (x & 7) {
}
}
>>
.globl _Switch4
.def _Switch4; .scl 2; .type 32; .endef
_Switch4:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
andl $7, %eax
cmpl $7, %eax
ja L12
jmp *L11(,%eax,4)
cmpl+ja are redundant in both cases.
Do you think it is possible for gcc t
Piotr Fusik <[EMAIL PROTECTED]> wrote:
> void Switch4(int x) {
> switch (x & 7) {
> case 0: printf("0\n"); break;
> case 1: printf("1\n"); break;
> case 2: printf("2\n"); break;
> case 3: printf("3\n"); break;
> case 4: printf("4\n"); break;
> case 5: printf("5\n"); bre
