`Instruction.getDefinitionOverlap()` depends on `SSAConstruction::getMemoryOperandDefinition()`, which in turn depends on `SSAConstruction::hasMemoryOperandDefinition()`. When the definition in question came from a `Chi` instruction, `hasMemoryOperandDefinition()` incorrectly bound `overlap` to the overlap relationship between the original (non-`Chi`) instruction and the use. The fix is to make use of the `actualDefLocation` parameter to `getDefinitionOrChiInstruction()`, which specifies the location for the result of the `Chi` in that case.
The result of `getDefinitionOverlap()` should never be `MayPartiallyOverlap`, because if that were the case, we should have inserted as `Chi` instruction and hooked the definition up to that instead.
There are quite a few existing failures.
This adds a taint step from `pred` to (the post-update node) of `succ` in `succ[idx] = pred` and its syntactic variants.
Unlike for structs, where partially tainted values are quite common, the theory is that arrays, maps, and slices are usually either completely tainted or completely clean.
This predicate replaces `isChiForAllAliasedMemory`, which was always
intended to be temporary. A test is added to `IRSanity.qll` to verify
that the new predicate corresponds exactly with (a fixed version of) the
old one.
The implementation of the new predicate,
`Cached::hasConflatedMemoryResult` in `SSAConstruction.qll`, is faster
to compute than the old `isChiForAllAliasedMemory` because it uses
information that's readily available during SSA construction.
In the Unix ABI, `std::va_list` is defined as `typedef struct __va_list_tag { ... } va_list[1];`, which means that any `std::va_list` used as a function parameter decays to `struct __va_list_tag*`. Handling this actually made the QL code slightly cleaner. The only tricky bit is that we have to determine what type to use as the actual `va_list` type when loading, storing, or modifying a `std::va_list`. To do this, we look at the type of the argument to the `va_*` macro. A detailed QLDoc comment explains the details.
I added a test case for passing a `va_list` as an argument, and then manipulating that `va_list` in the callee.
