similar to: [LLVMdev] RFC: Exception Handling Proposal II

On Nov 24, 2010, at 2:59 AM, Renato Golin wrote: > Hi Bill, > > First, I like the idea of being more expressive in IR, since the old > exception handling style didn't quite express exception handling, but > alternate paths (resume/unwind). That made DwarfException.cpp a big > hack. ;) > > It also makes the front-end engineer's life a lot easier, since there >

Hi Bill, this proposal seems strangely complicated. I don't see the advantage of the dispatch instruction over just attaching the information to each invoke. Right now you have invoke void @_Z3foov() to label %invcont unwind label %catch.handlers catch.handlers: landingpad dispatch resume to label %... catches [ %struct.__fundamental_type_info_pseudo* @_ZTIi, label

This is a revision of the second exception handling proposal I sent out. You can see it here: http://lists.cs.uiuc.edu/pipermail/llvmdev/2010-November/036484.html After much discussion, there are some changes to the proposal – some significant and some minor. One major point, this proposal does not address the issue of catching an exception thrown from a non-invoke instruction. However if done

Hi Bill, First, I like the idea of being more expressive in IR, since the old exception handling style didn't quite express exception handling, but alternate paths (resume/unwind). That made DwarfException.cpp a big hack. ;) It also makes the front-end engineer's life a lot easier, since there is less need to keep a long list of global state for all current landing pads, clean up areas,

On Dec 1, 2010, at 10:20 AM, Duncan Sands wrote: > Hi Bill, this proposal seems strangely complicated. I don't see the advantage > of the dispatch instruction over just attaching the information to each invoke. > Right now you have > > invoke void @_Z3foov() > to label %invcont unwind label %catch.handlers > > catch.handlers: landingpad > dispatch resume

On 24 November 2010 13:27, Bill Wendling <wendling at apple.com> wrote: > There are two different bits of information in the proposal that address this: the "unwind edge" from the invoke and the region number. It's the "unwind edge" which carries the bit of information that you're asking about. My mental view of this is that the region number correlates to the

Here is an alternative proposal to Bill's. It is closer to what we already have (which can be seen as a good or a bad thing!), and is also closer to what gcc does. It is more incremental than Bill's and introduces fewer new concepts. Executive summary ----------------- Remove the personality and list of catches out of eh.selector and stick them directly on invoke instructions. The

On Dec 1, 2010, at 1:37 PM, Duncan Sands wrote: > Executive summary > ----------------- > > Remove the personality and list of catches out of eh.selector and stick them > directly on invoke instructions. > > The invoke instruction > ---------------------- > > The invoke instruction is modified by adding extra catch info to it: > > <result> = invoke

Hi Bill, there are a couple of things I didn't understand about your proposal, for example how it interacts with inlining, whether it is feasible to do the "turn invoke-of-Unwind_Resume into a branch" optimization and also whether in "resumedest" you still plan to use _Unwind_Resume to continue unwinding up the stack. Could you please show what the LLVM IR would look like

Hi Bill, > This is similar to my first proposal. yup, I still consider your first proposal to have been basically sound. But it also suffers from a major problem, > which stopped that proposal dead in its tracks. Namely, you have information in > one place which needs to be shared in two different, but possibly disjoint, > places: the type, filters, and personality information. In

What? Yet another EH proposal?! This one is different from the others in that I'm planning to start implementing this shortly. But I want your feedback! I've all ready gotten a lot of feedback from Chris, John, Jim, Eric, and many others. Now is your turn! Please read this proposal and send me your comments, suggestions, and concerns. -bw

On Dec 1, 2010, at 1:37 PM, Duncan Sands wrote: > Inlining > -------- > > Many a plausible seeming exception handling scheme has fallen by the way-side > because it interacts poorly with inlining. > > Here is how inlining would work with this scheme. It's pretty close to how > it works right now. Suppose you have > > invoke void @foo() > to

On Dec 2, 2010, at 2:21 AM, Duncan Sands wrote: > Hi Bill, > >> This is similar to my first proposal. > > yup, I still consider your first proposal to have been basically sound. > > But it also suffers from a major problem, >> which stopped that proposal dead in its tracks. Namely, you have information in >> one place which needs to be shared in two

The poor interaction between exception handling and inlining in LLVM is one of the main motivations for the new exception handling models proposed recently. Here I give my analysis of the origin of the problem in the hope of clarifying the situation. Soon after dwarf exception handling was implemented in LLVM, I noticed that some programs would fail when compiled at -O3, for example the

On Dec 1, 2010, at 12:10 AM, John McCall wrote: > On Nov 30, 2010, at 11:04 PM, Bill Wendling wrote: >> • A landing pad must have exactly one dispatch instruction associated with it, >> and it must dominate that instruction. > > Okay, but how do we find it? > We can modify the dispatch to point back to the landing pad it's associated with. Something like: lpad:

I've been looking into a new way to implement exception handling in LLVM. The current model has many disadvantages, in my opinion. I try to address them with this proposal. I also try to make exception handling much more understandable to the normal human reader. :-) Any new proposal will need to address all present and future languages' exception handling methodologies. I

Hi all, Following John's, Duncan's and Bill's proposals about exception handling, I thought I'd summarise what has been discussed so far. ** The problems we're trying to solve are: P1. Different languages have different EH concepts and IR needs to be agnostic (as possible) about that P2. Inlining and optimisations (currently) destroy the EH semantics and produce code that

Hi Bill, there is clearly a misunderstanding: either I am missing something essential or you are. To clear this up, I suggest you send me evil examples and I will show you how my scheme handles them (or doesn't handle them, if I am indeed failing to see something). > This is the code that G++ generates from the example in my proposal: ... > If the call to __Z3foov throws, we need to

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

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