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

[Matt Arsenault via llvm-commits]

================
@@ -3560,6 +3560,72 @@ static Value *foldOrOfInversions(BinaryOperator &I,
   return nullptr;
 }
 
+struct DecomposedBitMaskMul {
+  Value *X;
+  APInt Factor;
+  APInt Mask;
+};
+
+static std::optional<DecomposedBitMaskMul> matchBitmaskMul(Value *V) {
+  Instruction *Op = dyn_cast<Instruction>(V);
+  if (!Op)
+    return std::nullopt;
+
+  Value *MulOp = nullptr;
+  const APInt *MulConst = nullptr;
+  if (match(Op, m_Mul(m_Value(MulOp), m_APInt(MulConst)))) {
+    Value *Original = nullptr;
+    const APInt *Mask = nullptr;
+    if (!MulConst->isStrictlyPositive())
+      return std::nullopt;
+
+    if (match(MulOp, m_And(m_Value(Original), m_APInt(Mask)))) {
+      if (!Mask->isStrictlyPositive())
+        return std::nullopt;
+      DecomposedBitMaskMul Ret;
+      Ret.X = Original;
+      Ret.Mask = *Mask;
+      Ret.Factor = *MulConst;
+      return Ret;
----------------
arsenm wrote:

```suggestion
      return { Original, *Mask, *MulConst};
```

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