- Split up the `last` predicate into a non-recursive part `lastNonRec` and a recursive
part `last`.
- Almost all syntactic constructs have a very simple `last` definition; a set of
disjuncts with exactly one recursive call -- those are defined in `lastNonRec`.
- `try` statements and (last) `catch` clauses require multiple recursive calls in
the same disjunct, and are therefore handled in the `last` predicate (as before).
- The benefit is that we only need to take care of the join order in the recursive
call (for non-`try`/`catch` statements) in one place (the predicate `lastRec`),
so we can get rid of many `nomagic`'ed `last`-specialisations.
- Add `Caching.qll` for controlling caching across multiple files.
- Move `isUncertainRefCall()` out of cached module in `Assignable.qll` to avoid
collapsing with CFG stage.
- Remove dependency on `AlwaysNullExpr` in `NullValue::getAnExpr()` to avoid
collapsing with CFG stage.
- Avoid caching pre-SSA library as it should only be used during the CFG construction
stage.
For methods compiled without optimization (and possibly also with optimization),
it is possible for a variable update to have multiple possible assigned values.
For example, the non-optimized CIL for
```
return cond ? null : "not null"
```
is
```
0: nop
1: ldarg.0
2: ldfld cond
3: brtrue.s 6:
4: ldstr "not null"
5: br.s 7:
6: ldnull
7: stloc.0 L0 // stores either `null` or "not null"
8: br.s 9:
9: ldloc.0
10: ret
```
Consequently, an existential in `CallableReturns.qll` must be a `forex`.
- Extract names of properties in a propery match, using the `exprorstmt_name` relation.
- Simplify extraction of properties by not distinguishing between top-level patterns
and nested patterns.
- Introduce `PatternExpr` to capture patterns in `is` expressions, `case` statements,
and `switch` expression arms.
- Generalize `IsTypeExpr`, `IsPatternExpr`, `IsRecursivePatternExpr`, and `IsConstantExpr`
to just `IsExpr` with a member predicate `PatternExpr getPattern()`.
- Generalize `TypeCase`, `RecursivePatternCase`, and `ConstCase` to just `CaseStmt` with
a member predicate `PatternExpr getPattern()`.
- Introduce classes `Switch` and `Case` as base classes of switch statements/expressions
and case statements/switch expression arms, respectively.
- Simplify CFG logic using the generalized classes.
- Generalize guards library to cover `switch` expressions tests.
- Generalize data flow library to cover `switch` expression assignments.
