[InstCombine] not(sub X, Y) --> add (not X), Y
The tests with constants show a missing optimization.
Analysis for adds is better than subs, so this can also
help with other transforms. And codegen is better with
adds for targets like x86 (destructive ops, no sub-from).
https://rise4fun.com/Alive/llK
llvm-svn: 338118
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index d1922cc..372bc41 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2545,6 +2545,10 @@
}
}
+ // ~(X - Y) --> ~X + Y
+ if (match(NotVal, m_OneUse(m_Sub(m_Value(X), m_Value(Y)))))
+ return BinaryOperator::CreateAdd(Builder.CreateNot(X), Y);
+
// ~(~X >>s Y) --> (X >>s Y)
if (match(NotVal, m_AShr(m_Not(m_Value(X)), m_Value(Y))))
return BinaryOperator::CreateAShr(X, Y);