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.
The `AliasedUse` instruction is supposed to represent future uses of aliased memory after the function returns. Since local variables from that function are no longer allocated after the function returns, the `AliasedUse` instruction should access only the set of aliased locations that does not include locals from the current stack frame.
This new instruction is the dual of the existing `AliasedDefinition` instruction. Whereas that instruction defines the contents of aliased memory before the function was called, `AliasedUse` represents the potential use of all aliased memory after the function returns. This ensures that writes to aliased memory do not appear "dead", even if there are no further reads from aliased memory within the function itself.
Expressions like the `e` in `e;` or `e, e2`, whose result is immediately
discarded, should not get a synthetic `CopyValue`. This removes a lot of
redundancy from the IR.
To prevent these expressions from being confused with the expressions
from which they get their result, the predicate
`getInstructionConvertedResultExpression` now suppresses results for
expressions that don't produce their own result. This should fix the
mapping between expressions and IR data-flow nodes.
The one interesting piece that needed to be fixed up was the type of an `Indirect[Read|Write]SideEffect` operand/result. If the parameter type is a pointer or reference to an incomplete type, we need to set the type of the side effect memory access to `Unknown`, because we don't model incomplete types in the IR type system.
I also added minimal support for `__assume` (generated as a `NoOp`), because lack of `__assume` support got in the way of debugging the other issue above.
