[LLVMdev] RFC: PerfGuide for frontend authors

[Philip Reames]

Just to be clear, you mean the release notes for 3.7 not 3.6 right?

On 03/04/2015 02:15 PM, Hans Wennborg wrote:
> 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:
>> http://llvm.org/docs/Frontend/PerformanceTips.html
>>
>> 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.
>>
>> Philip
>>
>>
>> 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.  :)
>>>
>>> Philip
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>>
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