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

[Matt Arsenault via llvm-commits]

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@@ -3641,6 +3707,22 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
             foldAddLikeCommutative(I.getOperand(1), I.getOperand(0),
                                    /*NSW=*/true, /*NUW=*/true))
       return R;
+
+    auto Decomp0 = matchBitmaskMul(I.getOperand(0));
+    auto Decomp1 = matchBitmaskMul(I.getOperand(1));
+
+    if (Decomp0 && Decomp1) {
+      if (Decomp0->X == Decomp1->X &&
+          (Decomp0->Mask & Decomp1->Mask).isZero() &&
+          Decomp0->Factor == Decomp1->Factor) {
+        auto NewAnd = Builder.CreateAnd(
+            Decomp0->X, ConstantInt::get(Decomp0->X->getType(),
+                                         (Decomp0->Mask + Decomp1->Mask)));
+
+        return BinaryOperator::CreateMul(
+            NewAnd, ConstantInt::get(NewAnd->getType(), Decomp1->Factor));
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arsenm wrote:

It appears you can preserve flags on the muls: https://alive2.llvm.org/ce/z/FYMcPK

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