[PATCH] D145545: [clang][Interp] Fix local variable (destructor) management in loop bodies

[Timm Bäder via Phabricator via cfe-commits]

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Ok, let me explain.

PREVIOUSLY:

When generating bytecode for a loop, we `visitStmt(Body)`, which will create its own local scope (that makes sense) and at the end of said scope, it will emit `Destroy` ops for all local variables, as well as emit code for the destructors of those local variables. However, the `Destroy` op calls the destructor for all data in the `Block`, and converts the blocks to `DeadBlock`s. That means the contents aren't usable anymore after it, and when we jump to the beginning of the loop and try to assign something to the block, we might end up trying to use the unusable data. This happens in the copy constructor of our `Pointer` class for example.

In pseudo code:

  loop {
      create locals...
  
     local destructors
     Destroy
     jump to beginning
  }

NOW:

I've split emitting the destructors for locals and emitting the `Destroy` op for a scope up into two separate parts. They are mostly still the same, i.e.when using a `AutoScope` or any of its subclasses, which emits the destructors and the `Destroy` op in its own destructor.

When visiting a loop, we create our own `LocalScope` to manage the lifetimes of locals created within the body and then call `emitDestructors` of that scope right before the `jmp` to the beginning of the loop. The `Destroy` op for the scope is emitted in the `LocalScope` destructor, so will only be emitted once.

In pseudo code:

  loop {
      create locals...
  
     local destructors
     jump to beginning
  }
  Destroy

The changes in this patch are on top of https://reviews.llvm.org/D137070, but the patch needs to go in before that //or// be merged with it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145545

Files:
  clang/lib/AST/Interp/ByteCodeExprGen.h
  clang/lib/AST/Interp/ByteCodeStmtGen.cpp
  clang/lib/AST/Interp/ByteCodeStmtGen.h

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