[InstCombine] (A + 1) + (B ^ -1) --> A - B
Turn canonicalized subtraction back into (-1 - B) and combine it with (A + 1) into (A - B).
This is similar to the folding already done for (B ^ -1) + Const into (-1 + Const) - B.
Differential Revision: https://reviews.llvm.org/D48535
llvm-svn: 335579
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 1101f72..330db9e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1212,6 +1212,11 @@
if (Value *V = checkForNegativeOperand(I, Builder))
return replaceInstUsesWith(I, V);
+ // (A + 1) + ~B --> A - B
+ // ~B + (A + 1) --> A - B
+ if (match(&I, m_c_BinOp(m_Add(m_Value(A), m_One()), m_Not(m_Value(B)))))
+ return BinaryOperator::CreateSub(A, B);
+
// X % C0 + (( X / C0 ) % C1) * C0 => X % (C0 * C1)
if (Value *V = SimplifyAddWithRemainder(I)) return replaceInstUsesWith(I, V);