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.
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.
This test used `getAQlClass`, which caused it to break when new classes
were added anywhere in the libraries. That's now avoided by switching to
`getCanonicalQLClass`. It turns out that `getCanonicalQLClass` didn't
support arithmetic expressions on complex numbers, so that support had
to be added.
Hopefully it does not make a difference in practice whether
uninstantiated template functions are considered to have control flow
through initializers of their static variables.
The C++ IR currently has a very clunky way of specifying the type of an IR entity (`Instruction`, `Operand`, `IRVariable`, etc.). There are three separate predicates: `getType()`, `isGLValue()`, and `getSize()`. All three are necessary, rather than just having a `getType()` predicate, because some IR entities have types that are not represented via an existing `Type` object in the AST. Examples include the type for an lvalue returned from a `VariableAddress` instruction, the type for an array slice being zero-initialized in a variable initializer, and several others. It is very easy for QL code to just check the `getType()` predicate, while forgetting to use `isGLValue()` to determine if that type is the actual type of the entity (the prvalue case) or the type referred to by a glvalue entity. Furthermore, the C++ type system creates potentially many different `Type` objects for the same underlying type (e.g. typedefs, using declarations, `const`/`volatile` qualifiers, etc.), making it more difficult to tell when two entities have semantically equivalent types.
In addition, other languages for which we want to enable the IR have somewhat different type systems. The various language type systems differ in their structure, although they tend to share the basic building blocks necessary for the IR.
To address all of the above problems, I've introduced a new class hierarchy, rooted at the class `IRType`, that represents a bare-bones type system that is independent of source language (at least across C/C++/C#/Java). A type's identity is based on its kind (signed integer, unsigned integer, floating-point, Boolean, blob, etc.), size and in the case of blob types, a "tag" to differentiate between different classes and structs. No distinction is made between, say `signed int` and plain `int`, or between different language integer types that have the same signedness and size (e.g. `unsigned int` vs. `wchar_t` on Linux). `IRType` is intended for use by language-agnostic IR-based analyses, including range analysis, dataflow, SSA construction, and alias analysis. The set of available `IRType`s is determined by predicate provided by the language library implementation (e.g. `hasSignedIntegerType(int byteSize)`.
In addition to `IRType`, each language now defines a type alias named `LanguageType`, representing the type of an IR entity in more language-specific terms. The only predicate requried on `LanguageType` is `getIRType()`, which returns the single `IRType` object for the language-neutral representation of that `LanguageType`. All other predicates on and subclasses of `LanguageType` are language-specific. There may be many instances of `LanguageType` that map to a given `IRType`, to allow for typedefs, etc.
Most of the changes are mechanical changes in the IR construction code, to return the correct type for each IR entity. SSA construction has also been updated to avoid dependencies on language-specific types.
I have not yet removed the original `getType()` predicates that just return `Type`. These can be removed once we move the remaining existing libraries to use `IRType`.
Test results are, by design, pretty much unchanged. Once case changed for inline asm, because the previously IR generation for it played a little fast and loose with the input/output expressions. The test case now includes both input and output variables. The generated IR for `Conditional_LValue` is now more correct, because we now have a way to represent an lvalue of an lvalue. `syntax-zoo` is still a hot mess. Most of the changed outputs are due to wobble from having multiple functions with the same name, but with a slightly different order of evaluation due to the type changes. Others are wobble from already-invalid IR. A couple non-wobbly places have improved slightly, though.
The C# part of this change is waiting for #2005 to be merged, since that has some of the necessary C# implementation.
Generation of IDs for namespace members has been fixed to generate
unique IDs for variables of the same name but in different namespaces.
Update the same_name test to validate this.
