[LLVMdev] RFC - Adding an optimization report facility?

[Xinliang David Li]

On Thu, Mar 6, 2014 at 3:54 PM, Chris Lattner <clattner at apple.com> wrote:

> On Mar 6, 2014, at 11:07 AM, Diego Novillo <dnovillo at google.com> wrote:
>
> The context of this is performance analysis of generated code. My interest
> is to trace at a high-level the major decisions done by the various
> optimizers. For instance, when the inliner decides to inline foo into bar,
> or the loop unroller decides to unroll a loop N times, or the vectorizer
> decides to vectorize a loop body.
>
> ...
>
> Before I get too far into this, do folks think this is a good idea? I'm
> open to reasonable requests on how the facility should work, etc.
>
>
> This is a great idea, and many people would welcome it.  Please write up a
> concrete proposals about how this will work, and we can iterate on that
> though.
>
> My intent is to introduce an optimization report option to LLVM which
> passes will be able to use to indicate the major decisions they make.
> Initially, I am tempted to mimic GCC's -fopt-info (
> http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#index-fopt-info-747
> ).
>
>
> I'm not sure if this is the best design or not (having never used it) -
> what feedback have you heard from (non-compiler-hacker) people trying to
> use it?
>
> IMO, the hard part of doing something like this is getting the user
> experience right.  It does you no good to say "hey I unrolled a loop" if
> you don't have enough location information to tell the user *which* loop
> got unrolled.  The key is to give them actionable information, not just the
> output of -debug :-)
>

yep, the information will be useless without source/location information.

David

>
> -Chris
>
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