similar to: [LLVMdev] Making llvm.eh.actions work

Hi Reid, I'm trying to get a "big picture" view of everything that needs to be done for clang and llvm to support SEH and C++ exception handling for the "msvc" environment. I've put together a list, including work in progress, but I'm guessing that I've missed some details. Can you look this over and tell me if it matches your idea of what needs to be done?

Thanks, Reid. These are good points. So I guess that does take us back to something more like my original proposal. I like your suggestion of having some kind of “eh.actions” intrinsic to represent the outlining rather than the extension to landingpad that I had proposed. I was just working on something like that in conjunction with my second alternative idea. What I’d really like is to have

These are exactly the sorts of code transformations we want to allow by delaying the outlining until later. By keeping such code inlined in the parent function until after optimization, we enable a lot of core optimizations like SROA. For example, we should be able to completely eliminate wrappers like unique_ptr that would otherwise stay around due to the pointer escaped to the destructor call

> optimizing EH codepaths is not usually performance critical. >> Leaving aside the rest of the thread, I feel the need to refute this point in isolation. I've found that optimizing (usually simplifying and eliminating) exception paths ends up being *extremely* important for my workloads. Failing to optimize exception paths sufficiently tends to indirectly hurt things like inlining

Hi Reid, I’ve worked through a few scenarios, and I think this is converging. I’m attaching a new example, which extends the one we’ve been working through to handle a few more cases. I wasn’t sure what you intended the first i32 argument in an llvm.eh.actions entry to be. I’ve been using it as a place to store the eh state that I’m associating with the action, but that’s kind of circular

Hi Reid, Thanks for the input. You wrote: > The @_Z4testv.unwind.1 helper just calls ~Inner(), but not ~Outer. That’s actually intentional. The thing to keep in mind is that all of the landing pads are going to be effectively removed by the time the final object image is generated. They are just there to facilitate the table generation, and in the __CxxFrameHandler3 case they don’t mean

> We should also think about how to call std::terminate when cleanup dtors throw. The current representation for Itanium is inefficient. As a strawman, I propose making @__clang_call_terminate an intrinsic: … That sounds like a good starting point. > Chandler expressed strong concerns about this design, however, as @llvm.eh.get_capture_block adds an ordering constraint on CodeGen. Once

I was thinking about this last night, and I came up with a third alternative which I think looks very promising. It’s basically a re-working of the previous alternative to use the landingpad concept rather than arbitrary fake logic, but it uses a single landing pad for the entire function that mimics the logic of the personality function to dispatch unwinding calls and catch handlers. I believe

What follows is primarily addressed to Reid and David, but since it some of it is relevant to the Windows exception handling proposal under discussion, I thought I should copy the LLVMDev distribution list. Anyone interested should feel free to jump in and discuss. My primary purpose here is to talk about what I'm working on so that anyone who is also working on the same things can let me

Thanks for the additional information. Right now I’m experimenting with a mix of code compiled with MSVC and code compiled with clang, trying to get a C++ exception thrown and caught by the MSVC-compiled code across a function in the clang-compiled code. My goal here is to isolate a small part of what needs to be done in a way that lends itself to tinkering. I think this might lead me to the

I am working on adding support for C++ exception handling when compiling for a native Windows target (that is a target with "MSVC" specified as the environment). Because of differences between how the native Windows runtime handles exceptions and the Itanium-based model used by current LLVM exception handling code, I believe this will require some extensions to the LLVM IR, though

I don’t really have a good enough feeling for the landingpad syntax yet to comment on the most natural way to extend it yet, but creating a synthetic cleanup function to call from the personality function is what I was thinking. With the current (trunk +/- a couple of weeks) clang, compiling for an “x86_64-pc-windows-msvc” target, I’m seeing a landingpad that looks like this: lpad:

On Tue, May 19, 2015 at 2:16 PM, Kaylor, Andrew <andrew.kaylor at intel.com> wrote: > What follows is primarily addressed to Reid and David, but since it some > of it is relevant to the Windows exception handling proposal under > discussion, I thought I should copy the LLVMDev distribution list. Anyone > interested should feel free to jump in and discuss. > > > >

Hi, Have any decisions been made on where to put executable WinEH tests? Wherever they go, would it be helpful if I were to add some C++EH and/or SEH tests pulled from MSVC's test suite, since compatibility is the goal here? Thanks -Joseph From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Reid Kleckner Sent: Tuesday, May 19, 2015 5:56 PM To: Kaylor,

Hi Reid, I’ve been following your proposal, and I’d be interested in helping out if I can. My main interest right now is in enabling C++ exception handling in clang for native (i.e. not mingw/cygwin) Windows targets (both 32-bit and 64-bit), but if I understand things correctly that will be closely related to your SEH work under the hood. I’m still trying to get up to speed on what is and is

I think we should make a new svn repository for these. test-suite is the logical place, but it's way too bloated and has too much Unix specific baggage. I'd really like to have something that just uses lit, can be checked out into projects, and can be run as part of check-all, like the compiler-rt execution test suite. My suggestion is to call it 'execution-tests', and we can

On Fri, May 15, 2015 at 5:27 PM, Kaylor, Andrew <andrew.kaylor at intel.com> wrote: > I like the way this sorts out with regard to funclet code generation. > It feels very natural for Windows EH, though obviously not as natural for > non-Windows targets and I think it is likely to block some optimizations > that are currently possible with those targets. > Right, it will

We already have something like what you describe in the form of mingw support. It runs on Windows and handles exceptions using a DWARF-style personality function and (I think) an LLVM-provided implementation of the libc++abi library. What this doesn't do is provide interoperability with MSVC-compiled objects. For instance, you can't throw an exception from MSVC-compiled code and catch

On Mon, May 18, 2015 at 11:48 AM, Steve Cheng <steve.ckp at gmail.com> wrote: > On 2015-05-18 13:32:54 -0400, Reid Kleckner said: > >> >> Right, doing our own personality function is possible, but still has half >> the challenge of using __CxxFrameHandler3, and introduces a new runtime >> dependency that isn't there currently. Given that it won't save

Thanks, Hal. I hear what you are saying about the accuracy. The problem, from my perspective, is trying to explain to users what they are going to get. The constant folding may be as accurate as the lib call would have been, but it isn't necessarily value safe. I've been operating on the assumption that LLVM's FP optimizations are value safe unless fast math flags are used. For the