[InstCombine] simplify code for xor folds; NFCI

This is just a cleanup step. The TODO comments show
what is wrong with the 'and' version of the fold.
Fixing this should be part of recommitting:
rL300977

llvm-svn: 341405

1 files changed, 23 insertions, 40 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 8fa012d214e..19322dd6f5b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2769,46 +2769,29 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
   if (Instruction *FoldedLogic = foldBinOpIntoSelectOrPhi(I))
     return FoldedLogic;
 
-  {
-    Value *A, *B;
-    if (match(Op1, m_OneUse(m_Or(m_Value(A), m_Value(B))))) {
-      if (A == Op0) {                                      // A^(A|B) == A^(B|A)
-        cast<BinaryOperator>(Op1)->swapOperands();
-        std::swap(A, B);
-      }
-      if (B == Op0) {                                      // A^(B|A) == (B|A)^A
-        I.swapOperands();     // Simplified below.
-        std::swap(Op0, Op1);
-      }
-    } else if (match(Op1, m_OneUse(m_And(m_Value(A), m_Value(B))))) {
-      if (A == Op0) {                                      // A^(A&B) -> A^(B&A)
-        cast<BinaryOperator>(Op1)->swapOperands();
-        std::swap(A, B);
-      }
-      if (B == Op0) {                                      // A^(B&A) -> (B&A)^A
-        I.swapOperands();     // Simplified below.
-        std::swap(Op0, Op1);
-      }
-    }
-  }
-
-  {
-    Value *A, *B;
-    if (match(Op0, m_OneUse(m_Or(m_Value(A), m_Value(B))))) {
-      if (A == Op1)                                  // (B|A)^B == (A|B)^B
-        std::swap(A, B);
-      if (B == Op1)                                  // (A|B)^B == A & ~B
-        return BinaryOperator::CreateAnd(A, Builder.CreateNot(Op1));
-    } else if (match(Op0, m_OneUse(m_And(m_Value(A), m_Value(B))))) {
-      if (A == Op1)                                        // (A&B)^A -> (B&A)^A
-        std::swap(A, B);
-      const APInt *C;
-      if (B == Op1 &&                                      // (B&A)^A == ~B & A
-          !match(Op1, m_APInt(C))) {  // Canonical form is (B&C)^C
-        return BinaryOperator::CreateAnd(Builder.CreateNot(A), Op1);
-      }
-    }
-  }
+  // Y ^ (X | Y) --> X & ~Y
+  // Y ^ (Y | X) --> X & ~Y
+  if (match(Op1, m_OneUse(m_c_Or(m_Value(X), m_Specific(Op0)))))
+    return BinaryOperator::CreateAnd(X, Builder.CreateNot(Op0));
+  // (X | Y) ^ Y --> X & ~Y
+  // (Y | X) ^ Y --> X & ~Y
+  if (match(Op0, m_OneUse(m_c_Or(m_Value(X), m_Specific(Op1)))))
+    return BinaryOperator::CreateAnd(X, Builder.CreateNot(Op1));
+
+  // Y ^ (X & Y) --> ~X & Y
+  // Y ^ (Y & X) --> ~X & Y
+  if (match(Op1, m_OneUse(m_c_And(m_Value(X), m_Specific(Op0)))))
+    return BinaryOperator::CreateAnd(Op0, Builder.CreateNot(X));
+  // (X & Y) ^ Y --> ~X & Y
+  // (Y & X) ^ Y --> ~X & Y
+  // Canonical form with a non-splat constant is (X & C) ^ C; don't touch that.
+  // TODO: Why do we treat arbitrary vector constants differently?
+  // TODO: A 'not' op is better for analysis and codegen, but demanded bits must
+  //       be fixed to prefer that (otherwise we get infinite looping).
+  const APInt *Unused;
+  if (!match(Op1, m_APInt(Unused)) &&
+      match(Op0, m_OneUse(m_c_And(m_Value(X), m_Specific(Op1)))))
+    return BinaryOperator::CreateAnd(Op1, Builder.CreateNot(X));
 
   {
     Value *A, *B, *C, *D;