[InstCombine] fold add(zext(xor X, C), C) --> sext X when C is INT_MIN in the source type
The pattern may look more obviously like a sext if written as:
define i32 @g(i16 %x) {
%zext = zext i16 %x to i32
%xor = xor i32 %zext, 32768
%add = add i32 %xor, -32768
ret i32 %add
}
We already have that fold in visitAdd().
Differential Revision: https://reviews.llvm.org/D22477
llvm-svn: 276035
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 221a220..8cb124d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1047,6 +1047,16 @@
// X + (signbit) --> X ^ signbit
if (Val->isSignBit())
return BinaryOperator::CreateXor(LHS, RHS);
+
+ // Is this add the last step in a convoluted sext?
+ Value *X;
+ const APInt *C;
+ if (match(LHS, m_ZExt(m_Xor(m_Value(X), m_APInt(C)))) &&
+ C->isMinSignedValue() &&
+ C->sext(LHS->getType()->getScalarSizeInBits()) == *Val) {
+ // add(zext(xor i16 X, -32768), -32768) --> sext X
+ return CastInst::Create(Instruction::SExt, X, LHS->getType());
+ }
}
// FIXME: Use the match above instead of dyn_cast to allow these transforms