[LLVMdev] RFC: PerfGuide for frontend authors
hans at chromium.org
Wed Mar 4 14:15:06 PST 2015
This is great. Can you add it to the release notes?
On Fri, Feb 27, 2015 at 3:34 PM, Philip Reames
<listmail at philipreames.com> wrote:
> The first version of this document is now live:
> Please feel free to add to it directly. Alternatively, feel free to reply
> to this thread with text describing an issue that should be documented.
> I'll make sure text gets turned into patches.
> On 02/23/2015 04:46 PM, Philip Reames wrote:
>> I'd like to propose that we create a new Performance Guide document. The
>> target of this document will be frontend authors, not necessarily LLVM
>> contributors. The content will be a collection of items a frontend author
>> might want to know about how to generate LLVM IR which will optimize well.
>> Some ideas on topics that might be worthwhile:
>> - Prefer sext over zext when value is known to be positive in the language
>> (e.g. range checked index on a GEP)
>> - Avoid loading and storing first class aggregates (i.e. they're not well
>> supported in the optimizer)
>> - Mark invariant locations - i.e. link to !invariant.load and TBAA
>> constant flags
>> - Use globals not inttoptr for runtime structures - this gives you
>> dereferenceability information
>> - Use function attributes where possible (nonnull, deref, etc..)
>> - Be ware of ordered and atomic memory operations (not well optimized),
>> depending on source language, might be faster to use fences.
>> - Range checks - make sure you test with the IRCE pass
>> If folks are happy with the idea of having such a document, I volunteer to
>> create version 0.1 with one or two items. After that, we can add to it as
>> folks encounter ideas. The initial content will be fairly minimal, I just
>> want a link I can send to folks in reviews to record comments made. :)
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>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
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