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

[Nikita Popov via llvm-commits]

================
@@ -3675,49 +3742,26 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
                                    /*NSW=*/true, /*NUW=*/true))
       return R;
 
-    Value *Cond0 = nullptr, *Cond1 = nullptr;
-    const APInt *Op0Eq = nullptr, *Op0Ne = nullptr;
-    const APInt *Op1Eq = nullptr, *Op1Ne = nullptr;
-
-    //  (!(A & N) ? 0 : N * C) + (!(A & M) ? 0 : M * C) -> A & (N + M) * C
-    if (match(I.getOperand(0),
-              m_Select(m_Value(Cond0), m_APInt(Op0Eq), m_APInt(Op0Ne))) &&
-        match(I.getOperand(1),
-              m_Select(m_Value(Cond1), m_APInt(Op1Eq), m_APInt(Op1Ne)))) {
-
-      auto LHSDecompose =
-          decomposeBitTest(Cond0, /*LookThruTrunc=*/true,
-                           /*AllowNonZeroC=*/false, /*DecomposeAnd=*/true);
-      auto RHSDecompose =
-          decomposeBitTest(Cond1, /*LookThruTrunc=*/true,
-                           /*AllowNonZeroC=*/false, /*DecomposeAnd=*/true);
-
-      if (LHSDecompose && RHSDecompose && LHSDecompose->X == RHSDecompose->X &&
-          RHSDecompose->Mask.isPowerOf2() && LHSDecompose->Mask.isPowerOf2() &&
-          LHSDecompose->Mask != RHSDecompose->Mask &&
-          LHSDecompose->Mask.getBitWidth() == Op0Ne->getBitWidth() &&
-          RHSDecompose->Mask.getBitWidth() == Op1Ne->getBitWidth()) {
-        assert(Op0Ne->getBitWidth() == Op1Ne->getBitWidth());
-        assert(ICmpInst::isEquality(LHSDecompose->Pred));
-        if (LHSDecompose->Pred == ICmpInst::ICMP_NE)
-          std::swap(Op0Eq, Op0Ne);
-        if (RHSDecompose->Pred == ICmpInst::ICMP_NE)
-          std::swap(Op1Eq, Op1Ne);
-
-        if (!Op0Ne->isZero() && !Op1Ne->isZero() && Op0Eq->isZero() &&
-            Op1Eq->isZero() && Op0Ne->urem(LHSDecompose->Mask).isZero() &&
-            Op1Ne->urem(RHSDecompose->Mask).isZero() &&
-            Op0Ne->udiv(LHSDecompose->Mask) ==
-                Op1Ne->udiv(RHSDecompose->Mask)) {
-          auto NewAnd = Builder.CreateAnd(
-              LHSDecompose->X,
-              ConstantInt::get(LHSDecompose->X->getType(),
-                               (LHSDecompose->Mask + RHSDecompose->Mask)));
-
-          return BinaryOperator::CreateMul(
-              NewAnd, ConstantInt::get(NewAnd->getType(),
-                                       Op0Ne->udiv(LHSDecompose->Mask)));
-        }
+    // (!(A & N) ? 0 : N * C) + (!(A & M) ? 0 : M * C) -> A & (N + M) * C
+    // This also accepts the equivalent mul form of (A & N) ? 0 : N * C)
+    // expressions i.e. (A & N) * C
----------------
nikic wrote:

Here I'd also mention the mul form first. `(A & N) * C + (A & M) * C -> (A & (N + M)) & C` is the simpler case.

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