Post-recursion we can filter the forward cons-candidates to only include
those that met a read step, and similarly restrict the reverse flow
cons-candidates to those that met a store step.
This commit is a little bit risky, as it allows for some potentially bad
join-orders. The best order starts with the delta and proceeds with the
then functional `mid.getEnclosingCallable()` and `getLocalCallContext`.
In this order `localFlowEntry` becomes superfluous. The standard order
is however somewhat unwilling to choose this. If it picks
`getLocalCallContext` and `getEnclosingCallable` as the first join, the
result is really bad, but it appears that the existence of
`localFlowEntry` at least means that it'll do `localFlowEntry`,
`getEnclosingCallable`, `getLocalCallContext` in that order, which
appears to be acceptable, although it isn't optimal. Without the
`localFlowEntry` conjunct we end up with the worst case. We'll need to
watch this particular join-ordering until we get better join-ordering
directives.
A performance regression in `definitionByReferenceNodeFromArgument#ff`
was ultimately caused by a join on parameter indexes in
`DefinitionByReferenceNode.getArgument`. Joining on numbers in QL is
always fragile, and somehow the changes in #4432 had caused the join
order here to break.
Instead of tweaking the join order in the slow predicate itself, I added
`pragma[noinline]` to one of the predicates involved in the join on
parameter indexes. This should prevent us from getting similar
performance problems in the future when we write code that joins on
parameter numbers. Joining on indexes is always risky, but it's even
more risky when one of the predicates in the join is inlined by the
compiler and expands to further joins.
I tested performance by running `CgiXss.ql` on a ChakraCore snapshot.
Tuple counts before (I interrupted execution after five minutes or so):
(626s) Tuple counts for DataFlowUtil::definitionByReferenceNodeFromArgument#ff:
58162 ~0% {3} r1 = SCAN DataFlowUtil::DefinitionByReferenceNode#class#ff AS I OUTPUT I.<1>, -1, I.<0>
26934 ~0% {2} r2 = JOIN r1 WITH Instruction::IndexedInstruction#ff AS R ON FIRST 2 OUTPUT r1.<0>, r1.<2>
26934 ~1% {2} r3 = JOIN r2 WITH Instruction::SideEffectInstruction::getPrimaryInstruction_dispred#3#ff AS R ON FIRST 1 OUTPUT R.<1>, r2.<1>
26850 ~1% {2} r4 = JOIN r3 WITH Instruction::CallInstruction::getThisArgumentOperand_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r3.<1>
26850 ~0% {2} r5 = JOIN r4 WITH Operand::Operand::getDef_dispred#3#ff AS R ON FIRST 1 OUTPUT R.<1>, r4.<1>
26850 ~1% {2} r6 = JOIN r5 WITH Instruction::Instruction::getUnconvertedResultExpression_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r5.<1>
58162 ~0% {2} r7 = SCAN DataFlowUtil::DefinitionByReferenceNode#class#ff AS I OUTPUT I.<1>, I.<0>
58162 ~4% {3} r8 = JOIN r7 WITH Instruction::IndexedInstruction#ff AS R ON FIRST 1 OUTPUT R.<1>, r7.<1>, r7.<0>
4026581120 ~0% {4} r9 = JOIN r8 WITH Instruction::CallInstruction::getPositionalArgumentOperand_dispred#fff_102#join_rhs AS R ON FIRST 1 OUTPUT r8.<2>, R.<1>, r8.<1>, R.<2>
31154 ~4% {2} r10 = JOIN r9 WITH Instruction::SideEffectInstruction::getPrimaryInstruction_dispred#3#ff AS R ON FIRST 2 OUTPUT r9.<3>, r9.<2>
31154 ~8% {2} r11 = JOIN r10 WITH Operand::Operand::getDef_dispred#3#ff AS R ON FIRST 1 OUTPUT R.<1>, r10.<1>
31154 ~0% {2} r12 = JOIN r11 WITH Instruction::Instruction::getUnconvertedResultExpression_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r11.<1>
58004 ~0% {2} r13 = r6 \/ r12
return r13
Tuple counts after:
(0s) Tuple counts for DataFlowUtil::definitionByReferenceNodeFromArgument#ff:
385785 ~6% {2} r1 = SCAN DataFlowUtil::DefinitionByReferenceNode#class#ff AS I OUTPUT I.<1>, I.<0>
385785 ~0% {3} r2 = JOIN r1 WITH Instruction::IndexedInstruction#ff AS R ON FIRST 1 OUTPUT r1.<0>, r1.<1>, R.<1>
385785 ~1% {3} r3 = JOIN r2 WITH Instruction::SideEffectInstruction::getPrimaryInstruction_dispred#3#ff AS R ON FIRST 1 OUTPUT R.<1>, r2.<2>, r2.<1>
198736 ~4% {2} r4 = JOIN r3 WITH Instruction::CallInstruction::getPositionalArgument#fff AS R ON FIRST 2 OUTPUT R.<2>, r3.<2>
198736 ~0% {2} r5 = JOIN r4 WITH Instruction::Instruction::getUnconvertedResultExpression_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r4.<1>
385785 ~1% {3} r6 = SCAN DataFlowUtil::DefinitionByReferenceNode#class#ff AS I OUTPUT I.<1>, -1, I.<0>
186891 ~1% {2} r7 = JOIN r6 WITH Instruction::IndexedInstruction#ff AS R ON FIRST 2 OUTPUT r6.<0>, r6.<2>
186891 ~2% {2} r8 = JOIN r7 WITH Instruction::SideEffectInstruction::getPrimaryInstruction_dispred#3#ff AS R ON FIRST 1 OUTPUT R.<1>, r7.<1>
183201 ~3% {2} r9 = JOIN r8 WITH Instruction::CallInstruction::getThisArgumentOperand_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r8.<1>
183201 ~0% {2} r10 = JOIN r9 WITH Operand::Operand::getDef_dispred#3#ff AS R ON FIRST 1 OUTPUT R.<1>, r9.<1>
175449 ~8% {2} r11 = JOIN r10 WITH Instruction::Instruction::getUnconvertedResultExpression_dispred#ff AS R ON FIRST 1 OUTPUT R.<1>, r10.<1>
374185 ~3% {2} r12 = r5 \/ r11
return r12
