This removes a lot of flow steps, but it all seems to be flow that was
present twice: both exiting a `PartialDefNode` and a
`DefinitionByReferenceNode`. All `DefinitionByReferenceNode`s are now
`PartialDefNode`s.
There were two problems here.
1. The inline predicates `isInitialized` and `isValueInitialized` on
`ArrayAggregateLiteral` caused their callers to materialize every
`int` that was a valid index into the array. This was slow on huge
value-initialized arrays.
2. The `isInitialized` predicate was used in the `TInstructionTag` IPA
type, creating a numbered tuple for each integer in it. This seemed
to be entirely unnecessary since the `TranslatedElement`s using those
tags were already indexed appropriately.
My original fix in https://github.com/Semmle/ql/pull/1661 fixed my minimal test case, but did not fix the original failure in a Linux snapshot. The real fix is to simply not create a `TranslatedDeclarationEntry` for an extern declaration, and have `TranslatedDeclStmt` skip any such declarations. I've added a regression test for that case (multiple extern declarations with same location in a macro expansion, with control flow between them). I did verify that it generates correct IR, and that it fixes all of the "use not dominated by definition" failures in Linux.
The underlying extractor bug, that caused the above issue also caused PrintAST to print garbage. I've worked around the bug in PrintAST.qll.
I've also fixed a bug in the control flow for `try`/`catch`, where there was missing flow from the `CatchByType` of the last handler of a `try` to the enclosing handler (or `Unwind`). Hat tip to @AndreiDiaconu1 for spotting this bug.
Previously, where we had a function-scoped `DeclarationEntry` for an extern variable or function, we would generate a `NoOp` instruction for it. There's nothing wrong with this by itself, although it was unnecessary. However, I've hit an extractor issue (Jira ticket already opened) that commonly causes multiple `DeclStmt`s to share a single `DeclarationEntry` child on extern declarations, so removing the `NoOp` instructions is an easy way to work around the extractor issue.
