I didn't quite know where to place it for JS, so I tried my best :)
The canonical Python version might be changed in the future, but I wanted to
keep this change small.
This updates C#'s IR to share `TInstruction` across stages the same way C++ does. The only interesting part is that, since we have not yet ported full alias analysis to C#, I stubbed out the required parts of the aliased SSA interface in `AliasedSSAStub.qll`.
Each stage of the IR reuses the majority of the instructions from previous stages. Previously, we've been wrapping each reused old instruction in a branch of the `TInstruction` type for the next stage. This causes use to create roughly three times as many `TInstruction` objects as we actually need.
Now that IPA union types are supported in the compiler, we can share a single `TInstruction` IPA type across stages. We create a single `TInstruction` IPA type, with individual branches of this type for instructions created directly from the AST (`TRawInstruction`) and for instructions added by each stage of SSA construction (`T*PhiInstruction`, `T*ChiInstruction`, `T*UnreachedInstruction`). Each stage then defines a `TStageInstruction` type that is a union of all of the branches that can appear in that particular stage. The public `Instruction` class for each phase extends the `TStageInstruction` type for that stage.
The interface that each stage exposes to the pyrameterized modules in the IR is now split into three pieces:
- The `Raw` module, exposed only by the original IR construction stage. This module identifies which functions have IR, which `TRawInstruction`s exist, and which `IRVariable`s exist.
- The `SSA` module, exposed only by the two SSA construction stages. This identifiers which `Phi`, `Chi`, and `Unreached` instructions exist.
- The global module, exposed by all three stages. This module has all of the predicates whose implementation is different for each stage, like gathering definitions of `MemoryOperand`s.
Similarly, there is now a single `TIRFunction` IPA type that is shared across all three stages. There is a single `IRFunctionBase` class that exposes the stage-indepdendent predicates; the `IRFunction` class for each stage extends `IRFunctionBase`.
Most of the other changes are largely mechanical.
When building SSA, we'll be assuming that stack variables do not escape, at least until we improve our alias analysis. I've added a new `IREscapeAnalysisConfiguration` class to allow the query to control this, and a new `UseSoundEscapeAnalysis.qll` module that can be imported to switch to the sound escape analysis. I've cloned the existing IR and SSA tests to have both sound and unsound versions. There were relatively few diffs in the IR dump tests, and the sanity tests still give the same results after one change described below.
Assuming that stack variables do not escape exposed an existing bug where we do not emit an `Uninitialized` instruction for the temporary variables used by `return` statements and `throw` expressions, even if the initializer is a constructor call or array initializer. I've refactored the code for handling elements that initialize a variable to share a common base class. I added a test case for returning an object initialized by constructor call, and ensured that the IR diffs for the existing `throw` test cases are correct.
This commit removes fields from the responsibilities of `FlowVar.qll`.
The treatment of fields in that file was slow and imprecise.
It then adds another copy of the shared global data flow library, used
only to find local field flow, and it exposes that local field flow
through `localFlow` and `localFlowStep`.
This has a performance cost. It adds two cached stages to any query that
uses `localFlow`: the stage from `DataFlowImplCommon`, which is shared
with all queries that use global data flow, and a new stage just for
`localFlowStep`.
