We now output literals for accesses to members of template parameters:
So for `foo` in the following example:
```
template<typename T> void bar(T& t) {
T.foo(1)
}
```
This predicate was taking 39s on a snapshot of Facebook Fizz because it
had disjuncts like this:
43685 ~0% {1} r34 = JOIN Type::FunctionPointerIshType#f AS L WITH Type::Type::getUnspecifiedType_dispred#ff_10#join_rhs AS R ON FIRST 1 OUTPUT R.<1>
43685 ~1% {2} r35 = JOIN r34 WITH CppType::getTypeSize#ff AS R ON FIRST 1 OUTPUT R.<1>, r34.<0>
170371500 ~2% {2} r36 = JOIN r35 WITH IRType::IRSizedType#ff_10#join_rhs AS R ON FIRST 1 OUTPUT R.<1>, r35.<1>
43685 ~6% {2} r37 = JOIN r36 WITH IRType::IRFunctionAddressType#class#ff AS R ON FIRST 1 OUTPUT r36.<1>, r36.<0>
Instead of fixing the joins in `getIRTypeForPRValue` itself, I've
changed the `IRType::getByteSize` predicate such that the optimiser
knows how to join with it efficiently.
The disjunct shown above now looks like this instead:
43685 ~0% {1} r26 = JOIN Type::FunctionPointerIshType#f AS L WITH Type::Type::getUnspecifiedType_dispred#ff_10#join_rhs AS R ON FIRST 1 OUTPUT R.<1>
43685 ~1% {2} r27 = JOIN r26 WITH CppType::getTypeSize#ff AS R ON FIRST 1 OUTPUT R.<1>, r26.<0>
43685 ~6% {2} r28 = JOIN r27 WITH IRType::IRFunctionAddressType::getByteSize#ff_10#join_rhs AS R ON FIRST 1 OUTPUT r27.<1>, R.<1>
This is just good enough to cause no performance regressions and pass
the virtual-dispatch tests we have for `security.TaintTracking`. In
particular, it fixes the tests for `UncontrolledProcessOperation.ql`
when enabling `DefaultTaintTracking.qll`.
Note that Declaration::getTemplateArgumentType() and
Declaration::getTemplateArgumentValue() need to be public so that they
can be overriden in derived classes.
This was the minimal amount of predicates I could easily cache without
introducing extra cached stages. The predicates that are not cached
here, like `CppType::getTypeSize` and `getCanonicalLanguageType`, appear
to be cheap.
I've tested that this avoids recomputation of the IR type system by
running
grep -c 'Starting to evaluate predicate CppType::CppType::getIRType_dispred'
on the evaluator log for `IRSanity.ql`. It drops from 4 to 1. The
pretty-printed DIL drops from 79,175 lines to 76,326 lines.
