[InstCombine] try to fold 'sub' to 'not'
https://rise4fun.com/Alive/jDd
Patterns with add/sub combos can be improved using
'not' ops. This is better for analysis and may lead
to follow-on transforms because 'xor' and 'add' are
commutative/associative. It can also help codegen.
llvm-svn: 338200
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index aa31e0d..e79bdf7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -926,7 +926,13 @@
if (Instruction *NV = foldBinOpIntoSelectOrPhi(Add))
return NV;
- Value *X;
+ Value *X, *Y;
+
+ // add (sub X, Y), -1 --> add (not Y), X
+ if (match(Op0, m_OneUse(m_Sub(m_Value(X), m_Value(Y)))) &&
+ match(Op1, m_AllOnes()))
+ return BinaryOperator::CreateAdd(Builder.CreateNot(Y), X);
+
// zext(bool) + C -> bool ? C + 1 : C
if (match(Op0, m_ZExt(m_Value(X))) &&
X->getType()->getScalarSizeInBits() == 1)