[all-commits] [llvm/llvm-project] 89ba7e: [codegen] Emit missing cleanups for stmt-expr and ...

[Utkarsh Saxena via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 89ba7e183e6e2c64370ed1b963e54c06352211db
      https://github.com/llvm/llvm-project/commit/89ba7e183e6e2c64370ed1b963e54c06352211db
  Author: Utkarsh Saxena <usx at google.com>
  Date:   2024-04-10 (Wed, 10 Apr 2024)

  Changed paths:
    M clang/lib/CodeGen/CGCleanup.cpp
    M clang/lib/CodeGen/CGCleanup.h
    M clang/lib/CodeGen/CGDecl.cpp
    M clang/lib/CodeGen/CGExpr.cpp
    M clang/lib/CodeGen/CGExprAgg.cpp
    M clang/lib/CodeGen/CGExprCXX.cpp
    M clang/lib/CodeGen/CodeGenFunction.cpp
    M clang/lib/CodeGen/CodeGenFunction.h
    A clang/test/CodeGenCXX/control-flow-in-stmt-expr.cpp
    A clang/test/CodeGenCoroutines/coro-suspend-cleanups.cpp

  Log Message:
  -----------
  [codegen] Emit missing cleanups for stmt-expr and coro suspensions [take-2] (#85398)

Fixes https://github.com/llvm/llvm-project/issues/63818 for control flow
out of an expressions.

#### Background

A control flow could happen in the middle of an expression due to
stmt-expr and coroutine suspensions.

Due to branch-in-expr, we missed running cleanups for the temporaries
constructed in the expression before the branch.
Previously, these cleanups were only added as `EHCleanup` during the
expression and as normal expression after the full expression.

Examples of such deferred cleanups include:

`ParenList/InitList`: Cleanups for fields are performed by the
destructor of the object being constructed.
`Array init`: Cleanup for elements of an array is included in the array
cleanup.
`Lifetime-extended temporaries`: reference-binding temporaries in
braced-init are lifetime extended to the parent scope.
`Lambda capture init`: init in the lambda capture list is destroyed by
the lambda object.

---

#### In this PR

In this PR, we change some of the `EHCleanups` cleanups to
`NormalAndEHCleanups` to make sure these are emitted when we see a
branch inside an expression (through statement expressions or coroutine
suspensions).

These are supposed to be deactivated after full expression and destroyed
later as part of the destructor of the aggregate or array being
constructed. To simplify deactivating cleanups, we add two utilities as
well:
* `DeferredDeactivationCleanupStack`: A stack to remember cleanups with
deferred deactivation.
* `CleanupDeactivationScope`: RAII for deactivating cleanups added to
the above stack.

---

#### Deactivating normal cleanups
These were previously `EHCleanups` and not `Normal` and **deactivation**
of **required** `Normal` cleanups had some bugs. These specifically
include deactivating `Normal` cleanups which are not the top of
`EHStack`
[source1](https://github.com/llvm/llvm-project/blob/92b56011e6b61e7dc1628c0431ece432f282b3cb/clang/lib/CodeGen/CGCleanup.cpp#L1319),
[2](https://github.com/llvm/llvm-project/blob/92b56011e6b61e7dc1628c0431ece432f282b3cb/clang/lib/CodeGen/CGCleanup.cpp#L722-L746).
This has not been part of our test suite (maybe it was never required
before statement expressions). In this PR, we also fix the emission of
required-deactivated-normal cleanups.



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