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

[via llvm-commits]

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@@ -4081,21 +4171,45 @@ Instruction *InstCombinerImpl::foldSelectICmp(ICmpInst::Predicate Pred,
 /// The Mask can be a constant, too.
 /// For some predicates, the operands are commutative.
 /// For others, x can only be on a specific side.
-static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
-                                          InstCombiner::BuilderTy &Builder) {
+static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I, const SimplifyQuery &Q,
+                                          InstCombiner &IC) {
+
+  Value *X, *M;
+  ICmpInst::Predicate Pred = I.getPredicate();
   ICmpInst::Predicate SrcPred;
-  Value *X, *M, *Y;
-  auto m_VariableMask = m_CombineOr(
-      m_CombineOr(m_Not(m_Shl(m_AllOnes(), m_Value())),
-                  m_Add(m_Shl(m_One(), m_Value()), m_AllOnes())),
-      m_CombineOr(m_LShr(m_AllOnes(), m_Value()),
-                  m_LShr(m_Shl(m_AllOnes(), m_Value(Y)), m_Deferred(Y))));
-  auto m_Mask = m_CombineOr(m_VariableMask, m_LowBitMask());
-  if (!match(&I, m_c_ICmp(SrcPred,
-                          m_c_And(m_CombineAnd(m_Mask, m_Value(M)), m_Value(X)),
-                          m_Deferred(X))))
-    return nullptr;
+  bool NeedsNot = false;
+
+  auto CheckMask = [&](Value *V, bool Not) {
+    if (!ICmpInst::isSigned(Pred))
+      return isMaskOrZero(V, Not, Q);
+    return Not ? match(V, m_NegatedPower2OrZero())
+               : match(V, m_LowBitMaskOrZero());
+  };
+
+  auto TryMatch = [&](unsigned OpNo) {
+    SrcPred = Pred;
+    if (match(I.getOperand(OpNo),
+              m_c_And(m_Specific(I.getOperand(1 - OpNo)), m_Value(M)))) {
+      X = I.getOperand(1 - OpNo);
+      if (OpNo)
+        SrcPred = ICmpInst::getSwappedPredicate(Pred);
+      return CheckMask(M, /*Not*/ false);
+    }
+    if (OpNo == 1 && match(I.getOperand(1), m_Zero()) &&
+        ICmpInst::isEquality(Pred) &&
+        match(I.getOperand(0), m_OneUse(m_And(m_Value(X), m_Value(M))))) {
+      NeedsNot = true;
+      if (IC.isFreeToInvert(X, X->hasOneUse()) && CheckMask(X, /*Not*/ true)) {
+        std::swap(X, M);
+        return true;
+      }
+      return IC.isFreeToInvert(M, M->hasOneUse()) && CheckMask(M, /*Not*/ true);
+    }
+    return false;
+  };
 
+  if (!TryMatch(0) && !TryMatch(1))
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goldsteinn wrote:

Done, commit to do so is split into NFC.

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