[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 +3593,78 @@ static Value *foldOrOfInversions(BinaryOperator &I,
   return nullptr;
 }
 
+// A decomposition of ((A & N) ? 0 : N * C) . Where X = A, Factor = C, Mask = N.
+// The NUW / NSW bools
+// Note that we can decompose equivalent forms of this expression (e.g. ((A & N)
+// * C))
+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;
+
+  Value *MulOp = nullptr;
+  const APInt *MulConst = nullptr;
+
+  // Decompose (A & N) * C) into BitMaskMul
+  if (match(Op, m_Mul(m_Value(MulOp), m_APInt(MulConst)))) {
+    Value *Original = nullptr;
+    const APInt *Mask = nullptr;
+    if (MulConst->isZero())
+      return std::nullopt;
+
+    if (match(MulOp, m_And(m_Value(Original), m_APInt(Mask)))) {
+      if (Mask->isZero())
+        return std::nullopt;
+      return std::optional<DecomposedBitMaskMul>(
+          {Original, *MulConst, *Mask,
+           cast<BinaryOperator>(Op)->hasNoUnsignedWrap(),
+           cast<BinaryOperator>(Op)->hasNoSignedWrap()});
+    }
+    return std::nullopt;
+  }
+
+  Value *Cond = nullptr;
+  const APInt *EqZero = nullptr, *NeZero = nullptr;
+
+  // Decompose ((A & N) ? 0 : N * C) into BitMaskMul
+  if (match(Op, m_Select(m_Value(Cond), m_APInt(EqZero), m_APInt(NeZero)))) {
+    auto ICmpDecompose =
+        decomposeBitTest(Cond, /*LookThruTrunc=*/true,
+                         /*AllowNonZeroC=*/false, /*DecomposeBitMask=*/true);
+    if (!ICmpDecompose.has_value())
+      return std::nullopt;
+
+    if (ICmpDecompose->Pred == ICmpInst::ICMP_NE)
+      std::swap(EqZero, NeZero);
+
+    if (!EqZero->isZero() || NeZero->isZero())
+      return std::nullopt;
+
+    if (!ICmpInst::isEquality(ICmpDecompose->Pred) ||
----------------
nikic wrote:

Can assert this.

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