[llvm] r299384 - [InstCombine] Remove canonicalization for (X & C1) | C2 --> (X | C2) & (C1|C2) when C1 & C2 have common bits.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Mon Apr  3 15:41:47 2017
New Revision: 299384

URL: http://llvm.org/viewvc/llvm-project?rev=299384&view=rev
Log:
[InstCombine] Remove canonicalization for (X & C1) | C2 --> (X | C2) & (C1|C2) when C1 & C2 have common bits.

It turns out that SimplifyDemandedInstructionBits will get called earlier and remove bits from C1 first. Effectively doing (X & (C1&C2)) | C2. So by the time it got to this check there could be no common bits.

I think the DAGCombiner has the same check but its check can be executed because it handles demanded bits later. I'll look at it next.


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=299384&r1=299383&r2=299384&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Mon Apr  3 15:41:47 2017
@@ -2122,17 +2122,6 @@ Instruction *InstCombiner::visitOr(Binar
 
   if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
     ConstantInt *C1 = nullptr; Value *X = nullptr;
-    // (X & C1) | C2 --> (X | C2) & (C1|C2)
-    // iff (C1 & C2) != 0.
-    if (match(Op0, m_And(m_Value(X), m_ConstantInt(C1))) &&
-        (RHS->getValue() & C1->getValue()) != 0 &&
-        Op0->hasOneUse()) {
-      Value *Or = Builder->CreateOr(X, RHS);
-      Or->takeName(Op0);
-      return BinaryOperator::CreateAnd(Or,
-                             Builder->getInt(RHS->getValue() | C1->getValue()));
-    }
-
     // (X ^ C1) | C2 --> (X | C2) ^ (C1&~C2)
     if (match(Op0, m_Xor(m_Value(X), m_ConstantInt(C1))) &&
         Op0->hasOneUse()) {