[LLVMdev] New EH representation for MSVC compatibility

[Philip Reames]

On 07/01/2015 04:45 PM, David Majnemer wrote:
>
>
> On Wed, Jul 1, 2015 at 4:42 PM, David Majnemer 
> <david.majnemer at gmail.com <mailto:david.majnemer at gmail.com>> wrote:
>
>
>
>     On Wed, Jul 1, 2015 at 2:10 PM, Joseph Tremoulet
>     <jotrem at microsoft.com <mailto: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.
I look forward to these patches.  Please CC me as a reviewer so that I 
see them; I'm a bit behind on commit traffic at the moment.

Please make sure the LangRef changes are reasonable complete when you 
post the patch.  The semantics will be the part I'm most concerned about.
>
>
>         Thanks
>
>         -Joseph
>
>         *From:*llvmdev-bounces at cs.uiuc.edu
>         <mailto:llvmdev-bounces at cs.uiuc.edu>
>         [mailto: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 <mailto: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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