[InstCombine] remove fold that swaps xor/or with constants; NFCI

// (X ^ C1) | C2 --> (X | C2) ^ (C1&~C2)

This canonicalization was added at:
https://reviews.llvm.org/rL7264 

By moving xors out/down, we can more easily combine constants. I'm adding
tests that do not change with this patch, so we can verify that those kinds
of transforms are still happening.

This is no-functional-change-intended because there's a later fold:
// (X^C)|Y -> (X|Y)^C iff Y&C == 0
...and demanded-bits appears to guarantee that any fold that would have
hit the fold we're removing here would be caught by that 2nd fold.

Similar reasoning was used in:
https://reviews.llvm.org/rL299384

The larger motivation for removing this code is that it could interfere with 
the fix for PR32706:
https://bugs.llvm.org/show_bug.cgi?id=32706

Ie, we're not checking if the 'xor' is actually a 'not', so we could reverse
a 'not' optimization and cause an infinite loop by altering an 'xor X, -1'. 

Differential Revision: https://reviews.llvm.org/D33050

llvm-svn: 302733

1 files changed, 0 insertions, 12 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index f7d9558ad27..629f9be8a0a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1986,18 +1986,6 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   if (Value *V = SimplifyBSwap(I))
     return replaceInstUsesWith(I, V);
 
-  if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
-    ConstantInt *C1 = nullptr; Value *X = nullptr;
-    // (X ^ C1) | C2 --> (X | C2) ^ (C1&~C2)
-    if (match(Op0, m_Xor(m_Value(X), m_ConstantInt(C1))) &&
-        Op0->hasOneUse()) {
-      Value *Or = Builder->CreateOr(X, RHS);
-      Or->takeName(Op0);
-      return BinaryOperator::CreateXor(Or,
-                            Builder->getInt(C1->getValue() & ~RHS->getValue()));
-    }
-  }
-
   if (isa<Constant>(Op1))
     if (Instruction *FoldedLogic = foldOpWithConstantIntoOperand(I))
       return FoldedLogic;