C++: Optimize SubBasicBlocks library #1824
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geoffw0
reviewed
Aug 26, 2019
| pragma[nomagic] | ||
| private int outerPosToInnerPos(BasicBlock bb, int posInBB) { | ||
| posInBB = result + this.getIndexInBasicBlock(bb) and | ||
| result = [ 0 .. this.getNumberOfNodes() - 1 ] |
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How confident are we that this isn't quadratic? Naively, it seems that for any particular node bb, posInBB, every possible this in bb must be checked.
Other than this question, FWIW, these changes LGTM also.
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This is the DIL we generate for this predicate:
noinline nomagic
SubBasicBlocks::SubBasicBlock::outerPosToInnerPos#ffff(/* SubBasicBlocks::SubBasicBlock */ cached entity this,
/* BasicBlocks::BasicBlock */ cached entity bb,
int posInBB, int result) :-
exists(cached int call_result |
exists(int range#high |
exists(int Sub#lhs |
SubBasicBlocks::SubBasicBlock::getIndexInBasicBlock#fff(this, bb,
call_result),
SubBasicBlocks::SubBasicBlock::getNumberOfNodes#ff(this, Sub#lhs),
Minus(Sub#lhs, 1, range#high)
),
range(0, range#high, result)
),
PlusInt(result, call_result, posInBB)
)
.
It first joins in the two getters (functional relations), so the tuple count will be the number of SubBasicBlock. It then joins with the range, which multiplies that tuple count by the average number of nodes per SubBasicBlock. All together, this predicate should have the same number of tuples as there are ControlFlowNodes.
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Great, that gives me a bit more confidence.
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Some predicates in this library had performance that was quadratic in the number of sub-basic-blocks per basic block. After field flow was added, that has become a problem on two projects: intel/mkl-dnn and laurentkneip/opengv. This PR should fix the join order and make these predicates faster on all projects.