Optimize bitwise even/odd test (-x&1 -> x&1) to not use negation.

Summary: We know that -x & 1 is equivalent to x & 1, avoid using negation for testing if a negative integer is even or odd.

Reviewers: majnemer

Subscribers: junbuml, mssimpso, gberry, mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D12156

llvm-svn: 245569

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -1273,6 +1273,10 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
         if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS, true, I))
           return BinaryOperator::CreateAnd(V, AndRHS);
 
+        // -x & 1 -> x & 1
+        if (AndRHSMask == 1 && match(Op0LHS, m_Zero()))
+          return BinaryOperator::CreateAnd(Op0RHS, AndRHS);
+
         // (A - N) & AndRHS -> -N & AndRHS iff A&AndRHS==0 and AndRHS
         // has 1's for all bits that the subtraction with A might affect.
         if (Op0I->hasOneUse() && !match(Op0LHS, m_Zero())) {

llvm/test/Transforms/InstCombine/and2.ll

@@ -77,3 +77,28 @@ define i1 @test8(i32 %i) {
   %cond = and i1 %cmp1, %cmp2
   ret i1 %cond
 }
+
+; combine -x & 1 into x & 1
+define i64 @test9(i64 %x) {
+; CHECK-LABEL: @test9(
+; CHECK-NOT: %sub = sub nsw i64 0, %x
+; CHECK-NOT: %and = and i64 %sub, 1
+; CHECK-NEXT: %and = and i64 %x, 1
+; CHECK-NEXT: ret i64 %and
+  %sub = sub nsw i64 0, %x
+  %and = and i64 %sub, 1
+  ret i64 %and
+}
+
+define i64 @test10(i64 %x) {
+; CHECK-LABEL: @test10(
+; CHECK-NOT: %sub = sub nsw i64 0, %x
+; CHECK-NEXT: %and = and i64 %x, 1
+; CHECK-NOT: %add = add i64 %sub, %and
+; CHECK-NEXT: %add = sub i64 %and, %x
+; CHECK-NEXT: ret i64 %add
+  %sub = sub nsw i64 0, %x
+  %and = and i64 %sub, 1
+  %add = add i64 %sub, %and
+  ret i64 %add
+}