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

[via llvm-commits]

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@@ -4082,23 +4172,37 @@ 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) {
-  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))))
+static Value *foldICmpWithLowBitMaskedVal(ICmpInst::Predicate Pred, Value *Op0,
+                                          Value *Op1, const SimplifyQuery &Q,
+                                          InstCombiner &IC) {
+
+  Value *X, *M;
+  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());
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goldsteinn wrote:

They seem about the same to me, happy to change.

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