[llvm-dev] How to run all available optimisations

[Mehdi Amini via llvm-dev]

Hi,

LLVM provides a facility to initialize a “standard” optimization pass pipeline in PassManagerBuilder, with multiple options (including the optimization level).

It is used in clang (clang/CodeGen/BackendUtil.cpp) or in opt.cpp (see AddOptimizationPasses()).

You can compare your pipeline to clang by trying: 

echo "" | clang -x c - -mllvm -debug-pass=Structure -c



— 
Mehdi


> On Sep 17, 2015, at 3:41 PM, Russell Wallace via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Given a generated module in memory, how do you run all available optimisations on it?
> 
> Tutorial section 4.3 at http://llvm.org/docs/tutorial/LangImpl4.html <http://llvm.org/docs/tutorial/LangImpl4.html> picks out just a few optimisations, which makes sense for a JIT compiler on short running code, but I'm looking at long-running code where it would be worthwhile to start off applying all of them and possibly selectively disable any that turn out not to be useful.
> 
> C:\llvm\tools\opt\opt.cpp seems to be a program that runs optimisations from IR to IR, and perhaps runs all of the applicable ones; main() seems to contain a list of optimisation pass initialisations (though only the ones applicable where we aren't generating machine code yet). Would copy-pasting the code from that file be the right starting point?
> 
> On the other hand, if so, I would have expected that code to occur again in the clang source tree, because clang likewise has a -O3 option, but it doesn't seem to. That suggests to me that I'm confused about how things are organized. What am I missing?
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