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

[Yingwei Zheng via llvm-commits]

================
@@ -1146,13 +1146,41 @@ 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)
-    return nullptr;
+  auto GetMatchPart = [&](ICmpInst *Cmp,
+                          unsigned OpNo) -> std::optional<IntPart> {
+    if (Pred == Cmp->getPredicate())
+      return matchIntPart(Cmp->getOperand(OpNo));
+
+    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) {
+      if (!match(Cmp->getOperand(1), m_Power2(C)) ||
+          !match(Cmp->getOperand(0), m_Xor(m_Value(), m_Value())))
+        return std::nullopt;
+    }
+
+    // (icmp ne (lshr x, C), (lshr y, C)) gets optimized to:
+    // (icmp ugt (xor x, y), (1 << C) - 1) so also look for that.
+    else if (Pred == CmpInst::ICMP_NE &&
+             Cmp->getPredicate() == CmpInst::ICMP_UGT) {
+      if (!match(Cmp->getOperand(1), m_LowBitMask(C)) ||
+          !match(Cmp->getOperand(0), m_Xor(m_Value(), m_Value())))
+        return std::nullopt;
+    } else {
+      return std::nullopt;
+    }
+
+    unsigned From = Pred == CmpInst::ICMP_NE ? C->popcount() : C->countr_zero();
+    Instruction *I = cast<Instruction>(Cmp->getOperand(0));
+    return {{I->getOperand(OpNo), From,
+             Cmp->getOperand(0)->getType()->getScalarSizeInBits() - From}};
----------------
dtcxzyw wrote:

```suggestion
             C->getBitWidth() - From}};
```
It would be simpler :)


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