[LLVMdev] New EH representation for MSVC compatibility

[David Majnemer]

On Wed, Jul 1, 2015 at 4:42 PM, David Majnemer <david.majnemer at gmail.com>
wrote:

>
>
> On Wed, Jul 1, 2015 at 2:10 PM, Joseph Tremoulet <jotrem at microsoft.com>
> wrote:
>
>>  Hi,
>>
>>
>>
>> I'd be interested in an updated summary as well, especially any thoughts
>> you have on when the various pieces might come online and where extra hands
>> could be helpful; we're eager to build our EH support in LLILC on top of
>> this.
>>
>
> A preliminary step was to push personality routines off of LandingPadInst
> and onto functions, this is already in trunk.
>
> On the IR front, we ended up with the following set of instructions:
>
> catcblock, catchret, cleanupblock, cleanupret, terminateblock
>
> Of these, I've locally added basic support for catchblock, catchret and
> cleanupret.  I'm working on cleanupblock and terminateblock as we speak.
>
> We'll still need to hook up CodeGenPrep and SDAG up to the new
> representation.
>
> Extra hands will be appreciated auditing LLVM's optimizations to ensure
> that they do not miscompile in the face of our new instructions.
>

And I forgot to mention: I hope to see the new instructions out for review
by the end of the week.


>
>
>>
>> Thanks
>>
>> -Joseph
>>
>>
>>
>>
>>
>> *From:* llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] *On
>> Behalf Of *Reid Kleckner
>> *Sent:* Thursday, June 18, 2015 12:22 PM
>> *To:* Philip Reames
>> *Cc:* Nick Lewycky; LLVM Developers Mailing List
>> *Subject:* Re: [LLVMdev] New EH representation for MSVC compatibility
>>
>>
>>
>> On Wed, Jun 17, 2015 at 6:18 PM, Philip Reames <listmail at philipreames.com>
>> wrote:
>>
>>  Since I haven't been following the thread closely, is there an updated
>> summary of the original proposal available?  I know that various parts I
>> had concerns with (the unsplitable blocks for instance) got addressed, but
>> I'm having trouble tracking all the changes in discussion.  Even just a
>> quick list of "and we changed X" would be helpful.
>>
>>
>>
>> We should do an updated summary, but I've been busy.
>>
>>
>>
>> We really do need to keep the unsplittable catchblocks, though.
>> Fundamentally, what we have is control flow described by data. This
>> proposal essentially adds LLVM instructions that model that data. We can't
>> insert real instructions like loads and stores between EH dispatch table
>> entries, so it's forbidden.
>>
>>
>>
>> We can compensate for all the other CFG merging operations after the fact
>> by duplicating code, but it's really hard to pattern match back EH dispatch
>> once it's been allowed to round trip through memory, phis, GVN, etc.
>>
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>>
>>
>
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