[LLVMdev] New EH representation for MSVC compatibility

[Joseph Tremoulet]

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.

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<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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