[cfe-dev] Running multiple ASTFrontendAction actions over list of source files

[Manuel Klimek via cfe-dev]

FrontendActions you return are owned by the compiler; the idea is to store
any data you need across multiple FrontendActions in a different data
structure, and have hand pointers to those through to your FA.

On Thu, Mar 22, 2018 at 3:23 PM João Paulo Labegalini de Carvalho via
cfe-dev <cfe-dev at lists.llvm.org> wrote:

> Hi,
>
> My name is João (some kind of brazilian version for John) and I am
> implementing a tool based using the libTooling framework. The goal of the
> tool is to performe Source-To-Source code transformations for later
> analysis/instrumentation through a LLVM Pass. The transformations will
> basically "mark" the start and end of OMPParallelFor loop bodies. The LLVM
> Pass will instrument all load/store instructions and hand their pointer
> operand to my runtime library. The runtime will attempt to detect
> loop-carried dependencies.
>
> Each transformation must be able to see the result of previous
> transformations, therefore I have implemented a slightly modified version
> of the ClangTool. I am attaching the source code containing the run method
> of my custom ClangTool class (a.k.a. CheckerTool).
>
> Right now my tool is able to successfully run multiple ASTFrontendAction
> actions over a single source file. However, as soon as ToolInvocation
> finishes processing a file, my custom ASTFrontendAction is destroyed. By
> inspecting the code of ToolInvocation::runInvocation method at
> lib/Tooling/Tooling.cpp I have found the culprit. The ToolInvocation object
> takes ownership of my ASTFrontendAction through a std::unique_ptr stored in
> the object ScopedToolAction. Looking through the history of the Tooling.cpp
> in the llvm/clang project on github I have found the commit which
> introduced such behavior (
> https://github.com/llvm-mirror/clang/commit/14a192435425af39e7f32b6e71613f9357e995f7#diff-bf9ab6da20a9d03d965b034c8c30a010
> ).
>
> The comment associated with such change tries to explain why it is
> necessary to delete the ToolAction as soon as the invocation ends, however
> I am failing to understand it. I would greatly appreciate if anyone of you,
> far more educated than myself on the inner workings of clang, could explain
> to me the mentioned comment ("ToolAction can have lifetime requirements for
> Compiler or its members.....").
>
> I was able to accomplish my goal by replacing the std:unique_ptr by a
> "conventional" pointer in the ToolInvocation::runInvocation method.
> Nonetheless, I fear for the completeness of my work-around.
>
> Best regards,
> --
> João Paulo L. de Carvalho
> Computer Science |  IC-UNICAMP | Campinas , SP - Brazil
> jaopaulolc at gmail.com
> joao.carvalho at ic.unicamp.br
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