similar to: How to call an (x86) cleanup/catchpad funclet

Hi, all, The intend of this thread is to complete the support for Windows SEH. Currently there are two major missing features: Jumping out of a _finally and Hardware exception handling. The document below is my proposed design and implementation to fully support SEH on LLVM. I have completely implemented this design on a branch in repo:

https://llvm.org/docs/ExceptionHandling.html#wineh > No variables live in to or out of the funclet can be allocated in registers. I don't think this is quite true. though it might be a useful simplification. Obviously it is true for volatile registers, but I believe the funclet receives a CONTEXT with the nonvolatiles restored. Obviously cumbersome to access, but it lets you enregister

I’ve been experimenting with SEH handling in LLVM, and it seems like the unwind funclets generated by LLVM are much larger than those generated by Microsoft’s CL compiler. I used the following code as a test: void test() { MyClass x; externalFunction(); } Compiling with CL, the unwind funclet that destroys ‘x’ is just two lines of asm: lea rcx, QWORD PTR x$[rdx] jmp ??1MyClass@@QEAA at XZ

I think this is the same underlying issue as https://bugs.llvm.org/show_bug.cgi?id=40320. CCing Reid, who's had a bunch of thoughts on this in the past. On 1/11/20, 10:25 AM, "llvm-dev on behalf of Chrulski, Christopher M via llvm-dev" <llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at lists.llvm.org> wrote: Hi, I've run into a bug with the LLVM

Is this example what you had in mind? void f() { int *p = get_p(); use_p(p); try { may_throw(p); } catch (int) { // don't need p } use_p(p); } The idea is that because p is not modified or used within the catch region (the funclet), it can live in a callee-saved register across the whole function. That is true, it is possible, but I don't think it fits very well in

I think the simplest, most complete, short term fix, would be to call llvm::colorEHFunclets, and to have the relevant instrumentation passes apply the appropriate funclet bundle when inserting function calls. It's not elegant because it means every simple instrumentation pass that inserts regular function calls (ASan, TSan, MSan, instrprof, etc) needs to be funclet-aware. But, it will work,

I've been looking at compilation time issues in the LICM pass, and it looks to me like colorEHFunclets() is probably being called a lot more often than it needs to be for functions that have Windows EH personality functions. For one thing, the funclet coloring is happening when computeLoopSafetyInfo() is called from LoopIdiomRecognize and LoopUnswitch but those passes don't use the

Bringing this back up for discussion on handling exceptions. According to the inalloca design <https://llvm.org/docs/InAlloca.html>, there should be a stackrestore after an invoke in both the non-exceptional and exceptional case (that doesn't seem to be happening in some cases as we've seen, but that's beside the point). Does it make sense to model a preallocated call as

``We all know'' that R has more flexible and nicer color specifications than S-plus. There are situations however, where I'd like to specify colors numerically, e.g. 1) convenience of using different colors in a for(.) loop or 2) backward compatibility with S. In S, there's the quite known ``standard'' col = 0 :<==> current background color [ = white by

On Wed, Jul 1, 2015 at 2:10 PM, Joseph Tremoulet <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

On Sat, Mar 28, 2020 at 2:20 PM Eli Friedman <efriedma at quicinc.com> wrote: > This would specifically be for cases where we try to rewrite the > signature? I would assume we should forbid rewriting the signature of a > call with an operand bundle. And once some optimization drops the bundle > and preallocated marking, to allow such rewriting, the signature doesn’t > need

> 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 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

In the past people in #llvm suggested to me I should use landing pads instead of seh when it comes to Windows unless i really need seh. Looking at what gets generated win64 -gnu does use seh but calls the landing pad somehow, while win32 doesn't at all. It looks to me a custom win64 landing pad personality can also deal with things like Access Violation. Is there a way to make win32 also

I think adding transitions to cleanupblocks on the normal execution path would be an optimization barrier. Most passes would see the cleanupblock instruction and run the other way. It's definitely appealing from the perspective of getting the smallest possible code, but I'm OK with having no more than two copies of everything in the finally block. I think with the addition of the

After a long tale of sorrow and woe, my colleagues and I stand here before you defeated. The Itanium EH representation is not amenable to implementing MSVC-compatible exceptions. We need a new representation that preserves information about how try-catch blocks are nested. WinEH background ------------------------------- Skip this if you already know a lot about Windows exceptions. On Windows,

This example is pretty compelling, but I still think I want to limit the scope of this change to not include this feature. It's probably reasonable to hold onto the idea as future work, though. In the meantime, frontends can decide for themselves whether they want code size or stronger optimization of cleanups by doing early outlining or not. The only way we can hit the quadratic growth from

On Sat, May 16, 2015 at 7:29 AM, Steve Cheng <steve.ckp at gmail.com> wrote: > On 2015-05-15 18:37:58 -0400, Reid Kleckner said: > > After a long tale of sorrow and woe, my colleagues and I stand here >> before you defeated. The Itanium EH representation is not amenable to >> implementing MSVC-compatible exceptions. We need a new representation that >> preserves

* When a goto in a _finally occurs, we must "unwind" to the target code, not just "jump" to target label I'm not sure what you're trying to say here. In the Microsoft ABI, goto out of a catch block also calls into the unwinder. We have to run any destructors, and return from the funclet (catchret/cleanupret). * The call inside a _try is an invoke with EH

Hello all, A few years ago, I added the inalloca feature to LLVM IR so that Clang could be C++ ABI compatible with MSVC on 32-bit x86. The feature works, but there is room for improvement. I recently took the time to write up a design using token values that will hopefully be better named and easier to work with and around. For the technical details of the proposal, I've written up the RFC