[LLVMdev] Proposal: split tools/opt/opt.cpp to OptTool and a smaller main()

[Nick Lewycky]

What exactly do you have in mind? The reusable part of what opt does is 
already factored into the pass manager builder. Everything else is file 
I/O, debugging, or flags management.

Put another way, opt is a collection of all the boiler plate you could 
ever want to use, but that's not a good line to refactor along. Having 
all this stuff -- let's take the flags as one example -- is sensible for 
opt because it's an internally facing tool for compiler developers, but 
it's not a reusable part.

Eli Bendersky wrote:
> Hello,
>
> I started some refactoring work on tools/opt/opt.cpp in r201116, but
> conceptually this is part of a larger effort. I'd like to consult with
> llvmdev@ about the best way to move this forward.
>
> Background: opt is a very useful swiss-army-knife tool, and its
> capabilities may be useful to custom tools. However, as it stands now
> opt is now very modular - almost all its functionality is contained
> within its main opt.cpp file.
>
> I think this is also the cause of some code duplication that currently
> exists between different LLVM tools. For example, some code from opt.cpp
> is duplicated in llc.cpp; the same is true for the logic of adding
> optimization passes between opt.cpp and Clang (a comment in opt.cpp even
> admits it "duplicates llvm-gcc behaviour", showing its age :-) A lot of
> cl::opt definitions are duplicated between different tools and have to
> be kept in sync for consistency.
>
> What I'd like to see is most of opt's functionality moving outside of
> opt.cpp to make it reusable in other tools. For example, this could be
> encapsulated in a class named OptTool, or just a namespace with a bunch
> of utility functions, as well as cl::opt definitions.
>
> Such a transition can be done in steps: the first step would be to
> create this OptTool within tools/opt. This would immediately enable
> building custom opt-based tools by linking in the code from tools/opt,
> leaving tools/opt/opt.cpp out. A more ambitious step would be to move
> the functionality to a library (lib/Tools?) - enabling code reuse
> between different LLVM tools as well as easier use within custom tools.
>
> Any opinions / suggestions welcome. I'll be happy to send out piecemeal
> patches that implement this refactoring.
>
> Eli
>
>
>
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