[llvm] [InstCombine] Improve eq/ne by parts to handle ult/ugt equality pattern (PR #69884)

[Yingwei Zheng via llvm-commits]

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@@ -1179,13 +1179,57 @@ Value *InstCombinerImpl::foldEqOfParts(ICmpInst *Cmp0, ICmpInst *Cmp1,
     return nullptr;
 
   CmpInst::Predicate Pred = IsAnd ? CmpInst::ICMP_EQ : CmpInst::ICMP_NE;
-  if (Cmp0->getPredicate() != Pred || Cmp1->getPredicate() != Pred)
+  auto MatchPred = [&](ICmpInst *Cmp) -> std::pair<bool, const APInt *> {
+    if (Pred == Cmp->getPredicate())
+      return {true, nullptr};
+
+    const APInt *C;
+    // (icmp eq (lshr x, C), (lshr y, C)) gets optimized to:
+    // (icmp ult (xor x, y), 1 << C) so also look for that.
+    if (Pred == CmpInst::ICMP_EQ && Cmp->getPredicate() == CmpInst::ICMP_ULT)
+      return {match(Cmp->getOperand(1), m_APInt(C)) && C->isPowerOf2() &&
+                  match(Cmp->getOperand(0), m_Xor(m_Value(), m_Value())),
+              C};
+
+    // (icmp ne (lshr x, C), (lshr y, C)) gets optimized to:
+    // (icmp ugt (xor x, y), (1 << C) - 1) so also look for that.
+    if (Pred == CmpInst::ICMP_NE && Cmp->getPredicate() == CmpInst::ICMP_UGT)
+      return {match(Cmp->getOperand(1), m_APInt(C)) && C->isMask() &&
+                  !C->isAllOnes() &&
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dtcxzyw wrote:

Should we add a negative test for this case? (I guess it will be simplified by `visitICmp`.)


https://github.com/llvm/llvm-project/pull/69884