[llvm-dev] How to invoke simplifycfg from code

[Hal Finkel via llvm-dev]

----- Original Message -----
> From: "Russell Wallace" <russell.wallace at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "llvm-dev" <llvm-dev at lists.llvm.org>
> Sent: Sunday, September 20, 2015 8:15:19 AM
> Subject: Re: [llvm-dev] How to invoke simplifycfg from code
> 
> 
> Okay, as far as I can see looking through the output of that, the
> empty block isn't created near the end, it exists at the start and
> never goes away.
> 

But running SimplifyCFG has a stand-alone pass removes it? That seems like a bug.

 -Hal

> 
> 
> On Sun, Sep 20, 2015 at 1:36 PM, Hal Finkel < hfinkel at anl.gov >
> wrote:
> 
> 
> Hi Russell,
> 
> Can you run your IR though opt with -O3 and -print-after-all and see
> when the block becomes empty?
> PassManagerBuilder::populateModulePassManager has, fairly near the
> end:
> 
> MPM.add(createCFGSimplificationPass());
> 
> but, other things do run afterward. Maybe we need another one of
> these closer to the end?
> 
> One other thing to realize is that an empty block like this might not
> actually turn up in any generated machine code because of how
> MachineBlockPlacement (and other MI-level passes) work.
> 
> -Hal
> 
> 
> 
> ----- Original Message -----
> > From: "Russell Wallace via llvm-dev" < llvm-dev at lists.llvm.org >
> > To: "llvm-dev" < llvm-dev at lists.llvm.org >
> > Sent: Sunday, September 20, 2015 1:28:56 AM
> > Subject: [llvm-dev] How to invoke simplifycfg from code
> > 
> > Simplifycfg doesn't get run by default even with -O3, but 'opt
> > -simplifycfg' can do it. I'm looking to add this functionality to
> > an
> > optimizer program that uses the llvm libraries. What's the best way
> > to do this? I don't really mind whether it becomes available as a
> > command line option as in opt, or I need to hardcode it as always
> > on.
> > 
> > 
> > To make it available as a command line option... I'm looking at the
> > code for opt, but it makes no reference to simplifycfg anywhere in
> > the code. I'm guessing it does something else that gets that option
> > linked in and somehow thereby connects that to activating the
> > actual
> > pass; how is this done?
> > 
> > 
> > Alternatively in an attempt to hardwire it I got as far as
> > FPM.add(new SimplifyCFGPass); but that fails to compile because
> > SimplifyCFGPass isn't of a compatible type, which indeed it isn't;
> > what should I be doing here?
> 
> 
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> > 
> 
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> 
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory