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
Based ontop of D104598, which is a NFCI-ish refactoring.
Here, a restriction, that only empty blocks can be merged, is lifted.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D104597
For example:
long long test(long long a, long long b) {
if (a << b > 0)
return b;
if (a << b < 0)
return a;
return a*b;
}
Produces:
sld. 5, 3, 4
ble 0, .LBB0_2
mr 3, 4
blr
.LBB0_2: # %if.end
cmpldi 5, 0
li 5, 1
isel 4, 4, 5, 2
mulld 3, 4, 3
blr
But the compare (cmpldi 5, 0) is redundant and can be removed (CR0 already
contains the result of that comparison).
The root cause of this is that LLVM converts signed comparisons into equality
comparison based on dominance. Equality comparisons are unsigned by default, so
we get either a record-form or cmp (without the l for logical) feeding a cmpl.
That is the situation we want to avoid here.
Differential Revision: https://reviews.llvm.org/D60506
Jason Molenda