[llvm] [InstCombine] Combine or-disjoint (and->mul), (and->mul) to and->mul (PR #136013)

[Nikita Popov via llvm-commits]

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@@ -3593,6 +3593,73 @@ static Value *foldOrOfInversions(BinaryOperator &I,
   return nullptr;
 }
 
+// A decomposition of ((X & Mask) ? 0 : Mask * Factor) . The NUW / NSW bools
+// track these properities for preservation. Note that we can decompose
+// equivalent forms of this expression (e.g. ((X & Mask) * Factor))
+struct DecomposedBitMaskMul {
+  Value *X;
+  APInt Factor;
+  APInt Mask;
+  bool NUW;
+  bool NSW;
+};
+
+static std::optional<DecomposedBitMaskMul> matchBitmaskMul(Value *V) {
+  Instruction *Op = dyn_cast<Instruction>(V);
+  if (!Op)
+    return std::nullopt;
+
+  const APInt *MulConst = nullptr;
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nikic wrote:

nit: Move this closer to `const APInt *Mask`.

https://github.com/llvm/llvm-project/pull/136013