[llvm] [InstCombine] fold `(icmp eq/ne (or disjoint x, C0), C1)` -> `(icmp eq/ne x, C0^C1)` (PR #87734)

[Nikita Popov via llvm-commits]

================
@@ -2049,6 +2050,16 @@ Instruction *InstCombinerImpl::foldICmpOrConstant(ICmpInst &Cmp,
   }
 
   Value *OrOp0 = Or->getOperand(0), *OrOp1 = Or->getOperand(1);
+
+  // (icmp eq/ne (or disjoint x, C0), C1)
+  //    -> (icmp eq/ne x, C0^C1)
+  if (Cmp.isEquality() && match(OrOp1, m_ImmConstant()) &&
+      cast<PossiblyDisjointInst>(Or)->isDisjoint()) {
+    Constant *NewC = ConstantExpr::getXor(
+        cast<Constant>(OrOp1), ConstantInt::get(OrOp1->getType(), C));
----------------
nikic wrote:

Use IRBuilder for this please, to save me the trouble of replacing it later.

https://github.com/llvm/llvm-project/pull/87734