InstCombine: Fold ((A | B) & C1) ^ (B & C2) -> (A & C1) ^ B if C1^C2=-1

Adapted from a patch by Richard Smith, test-case written by me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216157 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombine.h

@@ -152,6 +152,8 @@ public:
   Value *FoldOrOfFCmps(FCmpInst *LHS, FCmpInst *RHS);
   Instruction *FoldOrWithConstants(BinaryOperator &I, Value *Op, Value *A,
                                    Value *B, Value *C);
+  Instruction *FoldXorWithConstants(BinaryOperator &I, Value *Op, Value *A,
+                                    Value *B, Value *C);
   Instruction *visitOr(BinaryOperator &I);
   Instruction *visitXor(BinaryOperator &I);
   Instruction *visitShl(BinaryOperator &I);

lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -1983,6 +1983,38 @@ Instruction *InstCombiner::FoldOrWithConstants(BinaryOperator &I, Value *Op,
   return nullptr;
 }
 
+/// \brief This helper function folds:
+///
+///     ((A | B) & C1) ^ (B & C2)
+///
+/// into:
+///
+///     (A & C1) ^ B
+///
+/// when the XOR of the two constants is "all ones" (-1).
+Instruction *InstCombiner::FoldXorWithConstants(BinaryOperator &I, Value *Op,
+                                                Value *A, Value *B, Value *C) {
+  ConstantInt *CI1 = dyn_cast<ConstantInt>(C);
+  if (!CI1)
+    return nullptr;
+
+  Value *V1 = nullptr;
+  ConstantInt *CI2 = nullptr;
+  if (!match(Op, m_And(m_Value(V1), m_ConstantInt(CI2))))
+    return nullptr;
+
+  APInt Xor = CI1->getValue() ^ CI2->getValue();
+  if (!Xor.isAllOnesValue())
+    return nullptr;
+
+  if (V1 == A || V1 == B) {
+    Value *NewOp = Builder->CreateAnd(V1 == A ? B : A, CI1);
+    return BinaryOperator::CreateXor(NewOp, V1);
+  }
+
+  return nullptr;
+}
+
 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   bool Changed = SimplifyAssociativeOrCommutative(I);
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@@ -2165,6 +2197,18 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
       Instruction *Ret = FoldOrWithConstants(I, Op0, A, V1, D);
       if (Ret) return Ret;
     }
+    // ((A^B)&1)|(B&-2) -> (A&1) ^ B
+    if (match(A, m_Xor(m_Value(V1), m_Specific(B))) ||
+        match(A, m_Xor(m_Specific(B), m_Value(V1)))) {
+      Instruction *Ret = FoldXorWithConstants(I, Op1, V1, B, C);
+      if (Ret) return Ret;
+    }
+    // (B&-2)|((A^B)&1) -> (A&1) ^ B
+    if (match(B, m_Xor(m_Specific(A), m_Value(V1))) ||
+        match(B, m_Xor(m_Value(V1), m_Specific(A)))) {
+      Instruction *Ret = FoldXorWithConstants(I, Op0, A, V1, D);
+      if (Ret) return Ret;
+    }
   }
 
   // (A ^ B) | ((B ^ C) ^ A) -> (A ^ B) | C

test/Transforms/InstCombine/or-xor.ll

@@ -173,3 +173,11 @@ define i32 @test17(i32 %x, i32 %y) {
 ; CHECK-NEXT: %xor = xor i32 %x, %y
 ; CHECK-NEXT: ret i32 %xor
 }
+
+define i32 @test18(i32 %a, i32 %b) {
+  %or = xor i32 %a, %b
+  %and1 = and i32 %or, 1
+  %and2 = and i32 %b, -2
+  %xor = or i32 %and1, %and2
+  ret i32 %xor
+}