[LLVMdev] [WinEH] A hiccup for the Windows C++ exception handling

[Kaylor, Andrew]

I should clarify that the tests I’m talking about are compile-and-execute tests, so they will still be relevant to the re-designed implementation.  Unfortunately, I don’t have them integrated with any LLVM testing mechanism.  That’s something else I’ve been meaning to ask about.

Anyway, I think the results I’m seeing now are fairly significant, so I’d like to get these changes checked in -- especially given that it’s going to be a month or more before an alternate approach is ready.  I’d also like to talk about a transition plan so that we can minimize the backward steps taken as this is redesigned.  Maybe a command line option to enable the new IR generation until an end-to-end implementation is complete?

I’m working right now to clean up what I’ve done, but I should have it in a reviewable state today.  After that, I’ll try to create some lit-based tests that exercise the trouble spots that I am addressing.

I don’t have any objections to turning MSVC C++ exceptions off by default, but I think it’s possible that with these changes that might not be necessary.

-Andy

From: Reid Kleckner [mailto:rnk at google.com]
Sent: Thursday, May 14, 2015 9:12 AM
To: Kaylor, Andrew
Cc: David Majnemer; LLVM Developers Mailing List
Subject: Re: [WinEH] A hiccup for the Windows C++ exception handling

On Wed, May 13, 2015 at 4:37 PM, Kaylor, Andrew <andrew.kaylor at intel.com<mailto:andrew.kaylor at intel.com>> wrote:
I made some progress this afternoon.  I now have a set of changes in my local sandbox that allows clang to pass all of the tests in the suite I’ve been using to exercise this code.

How do you feel about working these changes into trunk to establish a working baseline, even knowing that parts of this are going to be redesigned?

I guess I'm kind of ambivalent about continuing in the current direction. It doesn't hurt, but if it provides someone with basic functionality for now, then that's OK. On the other hand, the tests won't be particularly valuable because Clang is going to emit new LLVM IR, so they'll need to be redone.

I also think that, given that the rewrite will take at least a month, we should turn MSVC C++ exceptions off by default in Clang until it's ready. We need some hidden flag that isn't /EHs. I'm already tired of getting bug reports along the lines of "clang crashed while compiling MSVC-style exceptions". Of course, the user can't tell from the crash that the workaround is just "turn off exceptions until they work". =/
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