To speed up the taint analysis in `NonConstantFormat.ql` and to remove
FPs that were due to taint spreading from `i` to `a[i]`, this commit
stops the taint tracking in `NonConstantFormat.ql` at every node that
could not possibly contain a string.
I tested performance on Wireshark, and it's fine. Pulling out the
`isSanitizerNode` prevented `isSanitizer` from turning into four
half-slow RA predicates due to both CPE and `#antijoin_rhs`
transformations happening.
It's sometimes faster but sometimes up to 2x slower to use plain
recursion here. On the other hand, plain recursion won't run out of Java
heap space, and it won't make unrelated computation slower by forcing
all RAM data out to disk.
The use of transitive closure for BB index calculation has been the
cause of an out-of-memory error. This commit switches the calculation to
use the `shortestDistances` HOP, which still has the problem that the
result needs to fit in RAM, but at least the RAM requirements are sure
to be linear in the size of the result. The `shortestDistances` HOP is
already used for BB index calculation for the C++ IR and for C#.
We could guard even better against OOM by switching the calculation to
use manual recursion, but that would undo the much-needed performance
improvements we got from #123.
This change improves performance on Wireshark, which is notorious for
having long basic blocks. When I benchmarked `shortestDistances`
for #123, it was slower than TC. With the current evaluator, it looks
like `shortestDistances` is faster. Performance before was:
PrimitiveBasicBlocks::Cached::getMemberIndex#ff ................... 9.7s (executed 8027 times)
#PrimitiveBasicBlocks::Cached::member_step#ffPlus ................. 6.6s
PrimitiveBasicBlocks::Cached::primitive_basic_block_entry_node#f .. 3.5s
PrimitiveBasicBlocks::Cached::primitive_basic_block_member#fff .... 2.3s
Performance with this commit is:
PrimitiveBasicBlocks::Cached::primitive_basic_block_entry_node#f ................................................................... 3.5s
shortestDistances@PrimitiveBasicBlocks::Cached::primitive_basic_block_entry_node#1@PrimitiveBasicBlocks::Cached::member_step#2#fff . 3s
PrimitiveBasicBlocks::Cached::primitive_basic_block_member#fff ..................................................................... 963ms
