The recent change to `AccessorCall` on dd99525566 resulted
in some bad join-orders, so I have (partly) reverted them. This means that the issues
orignally addressed by that change are now reintroduced, and I plan to instead apply a
fix to the CFG, which--unlike the original fix--should be able to handle multi-property-tuple
assignments.
This doesn't make it much faster, but it reduces the debug output
volume. It also simplifies the code.
I've found this change necessary when I compute the full IR on a
Wireshark snapshot in QL4E. Without it, Eclipse runs out of memory
because the console log is too large.
The new predicate `isOrphan` gets inlined into
`ignoreExprAndDescendants`, whose performance improves from
TranslatedElement::ignoreExprAndDescendants#f .. 23.4s (executed 9 times)
to
TranslatedElement::ignoreExprAndDescendants#f ... 4.3s (executed 9 times)
This dramatic improvement is not only due to eliminating a type check in
the recursive case. Removing the type check from the other base cases
also enabled them to get better join orders.
The previous reccomentation changed the behaviour of the code.
A user following the advice might have broken her/his code:
With call-by-value, the original parameter is not changed.
With a call-by-reference, however, it may be changed. To be sure,
nothing breaks by blindly following the advice, suggest to pass a
const reference.
The `SSAConstruction.getNewIRVariable` was very slow on Wireshark. This
was probably because it couldn't join on multiple columns
simultaneously. Instead of improving the join, I observed that the
`TIRVariable` type was the same between all three IR stages except for a
few occurrences of `FunctionIR` that could easily be changed to
`Function`. By sharing `TIRVariable` between all the stages, we avoid
recomputing it and translating it between every stage, turning the slow
`getNewIRVariable` predicate into a no-op.
This change means that later stages of the IR can't introduce new
variables, but that was already the case because
`config/identical-files.json` forced all three `IRVariable.qll` files to
be identical.
This predicate computed a local CP between all defs and uses of the same
virtual variable in a basic block. This wasn't a problem in
`unaliased_ssa`, but it became a huge problem in `aliased_ssa`, probably
because many variables can be modelled with a single virtual variable
there.
Before this commit, evaluation of `aliased_ssa`'s
`variableLiveOnEntryToBlock#ff#antijoin_rhs` on Wireshark took 80
_minutes_. After this commit, that predicate and its immediate
dependencies take around 5 _seconds_.
