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[Reassociate] Don't canonicalize X - undef to X + (-undef).

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Phabricator Revision: http://reviews.llvm.org/D5674
PR21205

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219434 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chad Rosier
2014-10-09 20:06:29 +00:00
parent 07200c4b6c
commit c2bf8fbdf4
2 changed files with 25 additions and 0 deletions
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4
lib/Transforms/Scalar/Reassociate.cpp
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@@ -967,6 +967,10 @@ static bool ShouldBreakUpSubtract(Instruction *Sub) {
if (BinaryOperator::isNeg(Sub) || BinaryOperator::isFNeg(Sub))
return false;
// Don't breakup X - undef.
if (isa<UndefValue>(Sub->getOperand(1)))
return false;
// Don't bother to break this up unless either the LHS is an associable add or
// subtract or if this is only used by one.
Value *V0 = Sub->getOperand(0);