[llvm] [InstCombine] Add combines for `(icmp eq/ne (and X, P2), (and X, -P2))` (PR #94867)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Sun Jun 9 12:08:12 PDT 2024
================
@@ -5570,10 +5570,35 @@ Instruction *InstCombinerImpl::foldICmpEquality(ICmpInst &I) {
Z = B;
}
- if (X) { // Build (X^Y) & Z
- Op1 = Builder.CreateXor(X, Y);
- Op1 = Builder.CreateAnd(Op1, Z);
- return new ICmpInst(Pred, Op1, Constant::getNullValue(Op1->getType()));
+ if (X) {
+ // (X&P2) == (X&-P2)
+ // -> X u< P2*2
+ // (X&P2) != (X&-P2)
+ // -> X u>= P2*2
+ // iff P2 is not INT_MIN
----------------
nikic wrote:
I don't understand why you need the specific high mask + low mask pattern. Why is my suggestion to check that `X^Y` is a high mask (or as @dtcxzyw pointed out, a negative power of two) and then fold to `<= ~(X^Y)` not sufficient?
This covers the case where X is a high mask and Y is a low mask of the high mask as a special case, but also covers other cases. E.g. `X = 0b1010, Y = 0b0100, X^Y = 0b1110` is also valid for this transform, does not have X or Y being a high mask themselves.
https://github.com/llvm/llvm-project/pull/94867
More information about the llvm-commits
mailing list