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

[Yingwei Zheng via llvm-commits]

================
@@ -4068,11 +4068,117 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
   return nullptr;
 }
 
+// Returns whether 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;
+  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:
+    if (match(V, m_Not(m_Value(X))))
+      return isMaskOrZero(X, !Not, Q, Depth);
+
+    // (X ^ (X - 1)) is a Mask
+    return !Not &&
+           match(V, m_c_Xor(m_Value(X), m_Add(m_Deferred(X), m_AllOnes())));
+  case Instruction::Select:
+    // c ? Mask0 : Mask1 is a Mask.
+    return isMaskOrZero(I->getOperand(1), Not, Q, Depth) &&
+           isMaskOrZero(I->getOperand(2), Not, Q, Depth);
+  case Instruction::Shl:
+    if (Not) {
+      // (-1 >> X) << X is ~Mask
+      if (match(I->getOperand(0),
+                m_Shr(m_AllOnes(), m_Specific(I->getOperand(1)))))
+        return true;
+
+      // (~Mask) << X is a ~Mask.
+      return isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+    }
+    break;
+  case Instruction::LShr:
+    if (!Not) {
+      // (-1 << X) >> X is a Mask
+      if (match(I->getOperand(0),
+                m_Shl(m_AllOnes(), m_Specific(I->getOperand(1)))))
+        return true;
+      // Mask >> X is a Mask.
+      return isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+    }
+    return false;
+  case Instruction::AShr:
+    // Mask s>> X is a Mask.
+    // ~Mask s>> X is a ~Mask.
+    return isMaskOrZero(I->getOperand(0), Not, Q, Depth);
+  case Instruction::Add:
+    // Pow2 - 1 is a Mask.
+    if (!Not && match(I->getOperand(1), m_AllOnes()))
+      return isKnownToBeAPowerOfTwo(I->getOperand(0), Q.DL, /*OrZero*/ true,
+                                    Depth, Q.AC, Q.CxtI, Q.DT);
+    break;
+  case Instruction::Sub:
+    // -Pow2 is a ~Mask.
+    if (Not && match(I->getOperand(0), m_Zero()))
+      return isKnownToBeAPowerOfTwo(I->getOperand(1), Q.DL, /*OrZero*/ true,
+                                    Depth, Q.AC, Q.CxtI, Q.DT);
+    break;
+  case Instruction::Invoke:
----------------
dtcxzyw wrote:

All the following intrinsics are `nounwind`.

```suggestion
```



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