[llvm] [InstCombine] Improve folding of `icmp pred (and X, Mask/~Mask), Y)` (PR #81562)

[Yingwei Zheng via llvm-commits]

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@@ -4068,11 +4068,115 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
   return nullptr;
 }
 
+// Returns of V is a Mask ((X + 1) & X == 0) or ~Mask (-Pow2OrZero)
+static bool isMaskOrZero(const Value *V, bool Not, const SimplifyQuery &Q,
+                         unsigned Depth = 0) {
+  if (Not ? match(V, m_NegatedPower2OrZero()) : match(V, m_LowBitMaskOrZero()))
+    return true;
+  if (V->getType()->getScalarSizeInBits() == 1)
+    return true;
+  if (Depth++ >= MaxAnalysisRecursionDepth)
+    return false;
+  Value *X;
+  if (match(V, m_Not(m_Value(X))))
+    return isMaskOrZero(X, !Not, Q, Depth);
+  const Operator *I = dyn_cast<Operator>(V);
+  if (I == nullptr)
+    return false;
+  switch (I->getOpcode()) {
+  case Instruction::ZExt:
+    // ZExt(Mask) is a Mask.
+    return !Not && isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::SExt:
+    // SExt(Mask) is a Mask.
+    // SExt(~Mask) is a ~Mask.
+    return isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::And:
+  case Instruction::Or:
+    // Mask0 | Mask1 is a Mask.
+    // Mask0 & Mask1 is a Mask.
+    // ~Mask0 | ~Mask1 is a ~Mask.
+    // ~Mask0 & ~Mask1 is a ~Mask.
+    return isMaskOrZero(I->getOperand(1), Not, Q, Depth) &&
+           isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::Xor:
+    // (X ^ (X - 1)) is a Mask
----------------
dtcxzyw wrote:

Is it a Mask or a ~Mask?

https://github.com/llvm/llvm-project/pull/81562