This trick for excluding elements from macro bodies but not macro
arguments looks promising and should probably be used much more. With
this commit, it's now easy to use from any query.
Performance is still good because the new predicate gets appropriately
magiced.
It's a bit crude to suppress all results in instantiations, but we're
already using this kind of suppression in `PointlessComparison.ql`
(without the `Self`) because there is no convenient alternative. It
means we lose some good results but also suppress a new false positive
in Boost that surfaced after we added support for non-type template
parameters.
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)
}
```
Previously, we didn't track string literals as known memory locations at all, so they all just got marked as `UnknownMemoryLocation`, just like an aribtrary read from a random pointer. This led to some confusing def-use chains, where it would look like the contents of a string literal were being written to by the side effect of an earlier function call, which of course is impossible.
To fix this, I've made two changes. First, each string literal is now given a corresponding `IRVariable` (specifically `IRStringLiteral`), since a string literal behaves more or less as a read-only global variable. Second, the `IRVariable` for each string literal is now marked `isReadOnly()`, which the alias analysis uses to determine that an arbitrary write to aliased memory will not overwrite the contents of a string literal.
I originally planned to treat all string literals with the same value as being the same memory location, since this is the usual behavior of modern compilers. However, this made implementing `IRVariable.getAST()` tricky for string literals, so I left them unpooled.
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.
