Add a comment when there is a shifted value,
add x9, x0, #291, lsl #12 ; =1191936
but not when the immediate value is unshifted,
subs x9, x0, #256 ; =256
when the comment adds nothing additional to the reader.
Differential Revision: https://reviews.llvm.org/D107196
ICMP & SELECT patterns extracting the sign of a value can be simplified
to OR & ASR (see https://alive2.llvm.org/ce/z/Xx4iZ0).
This does not save any instructions in IR, but it is profitable on
AArch64, because we need at least 2 extra instructions to materialize 1
and -1 for the SELECT.
The improvements result in ~5% speedups on loops of the form
static int sign_of(int x) {
if (x < 0) return -1;
return 1;
}
void foo(const int *x, int *res, int cnt) {
for (int i=0;i<cnt;i++)
res[i] = sign_of(x[i]);
}
Reviewed By: dmgreen
Differential Revision: https://reviews.llvm.org/D96596
Jason Molenda