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[reassociate] Switch two std::sort calls into std::stable_sort calls as

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their inputs come from std::stable_sort and they are not total orders.

I'm not a huge fan of this, but the really bad std::stable_sort is right
at the beginning of Reassociate. After we commit to stable-sort based
consistent respect of source order, the downstream sorts shouldn't undo
that unless they have a total order or they are used in an
order-insensitive way. Neither appears to be true for these cases.
I don't have particularly good test cases, but this jumped out by
inspection when looking for output instability in this pass due to
changes in the ordering of std::sort.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202196 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-02-25 21:54:50 +00:00
parent 431e9f0310
commit 9c256eccb3
1 changed files with 2 additions and 2 deletions
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4
lib/Transforms/Scalar/Reassociate.cpp
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@ -1292,7 +1292,7 @@ Value *Reassociate::OptimizeXor(Instruction *I,
// the same symbolic value cluster together. For instance, the input operand
// sequence ("x | 123", "y & 456", "x & 789") will be sorted into:
// ("x | 123", "x & 789", "y & 456").
std::sort(OpndPtrs.begin(), OpndPtrs.end(), XorOpnd::PtrSortFunctor());
std::stable_sort(OpndPtrs.begin(), OpndPtrs.end(), XorOpnd::PtrSortFunctor());
// Step 3: Combine adjacent operands
XorOpnd *PrevOpnd = 0;
@ -1618,7 +1618,7 @@ bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops,
// below our mininum of '4'.
assert(FactorPowerSum >= 4);
std::sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
std::stable_sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter());
return true;
}