<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Dec 18, 2014 at 4:50 PM, Kaylor, Andrew <span dir="ltr"><<a href="mailto:andrew.kaylor@intel.com" target="_blank">andrew.kaylor@intel.com</a>></span> wrote:<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
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<p class="MsoNormal">Hi Reid,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">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?<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Structured Exception Handling<u></u><u></u></p>
<p class="MsoNormal">---------------------------------------<u></u><u></u></p>
<p class="MsoNormal">* Add support for __try and __except in clang.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">It looks like this is mostly implemented by your changes in the D5607 review, but there hasn’t been any activity on that review for quite a while. You’re going to rewrite a lot of that to change the way filters are implemented, right?</p></div></div></blockquote><div><br></div><div>Yes. Basically I was trying to do things top-down at first, and then John seemed to want me to propose the LLVM IR design first so he could review it, so I switched over to doing things bottom up: MI, SDAG, IR, Clang.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal"><u></u></p>
<p class="MsoNormal">* Add support for __finally in clang<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I haven’t seen anything for this yet. Based on various discussions, it seems like you intend to mix C++ scope cleanup with SEH handlers in ways that MSVC specifically punts. Is that right?</p></div></div></blockquote><div><br></div><div>Supporting this is a non-goal for me, but I was planning to use the same vanilla LLVM IR cleanup model for __finally as for C++ cleanups. It wouldn't be hard to add a not-very-faithful mode that runs C++ destructor cleanups when non-inlined code faults.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal"><u></u></p>
<p class="MsoNormal">* Add support for unwinding in frames with no exception handlers<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I’m not clear as to what needs to be done for this. I know clang is intentionally generating errors when you compile code with an MSVC-environment target. I’m guessing that just removing this block will be sufficient for clang to generate
the IR we want. Then it will be up to the back end to produce the correct unwinding support, which I think it may already be doing.</p></div></div></blockquote><div><br></div><div>Do we not do this already? This shouldn't be hard, we already know how to emit the required pdata/xdata call frame information (CFI).</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div>
<p class="MsoNormal">* Add support for frame allocation intrinsics.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">You’ve started this in review D6493, which seems to be progressing. I don’t know how much remains to be done there, but I trust that you have it under control.</p></div></div></blockquote><div><br></div><div>Yep.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div>
<p class="MsoNormal">* Add support for outlining filter functions.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">This is partially implemented in my D6556 review. I think that will be ready to check in once the expected for of the input IR settles. I still need to add support for removing outlined code. It will also need to make use of the frame
allocation intrinsics to reference frame variables in the outlined code. You’ve mentioned that we should also do analysis to minimize the amount of duplicated code. I agree but I was hoping that could wait until everything else is in place and working.</p></div></div></blockquote><div><br></div><div>Yep.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div>
<p class="MsoNormal">* Add support for outlining __try bodies.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I don’t know what your plan is for identifying the beginning and end of these regions, but I expect that we’ll be able to leverage the outlining code from the task above to do most of the work for this task.</p></div></div></blockquote><div><br></div><div>I've already done this in Clang in D5607. We want to do this before LLVM optimizers remove or move around potentially trapping operations.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple">
<p class="MsoNormal">* Add support to emit .xdata table for SEH for 64-bit targets.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">This is implemented in your D6300 review, but that looks like it has stalled a bit. Is there anything holding this up other than lack of reviews?</p></div></blockquote><div><br></div><div>Just reviews. Eric took a look, and said he wants me to run around and update lots of comments referring to DWARF EH that isn't really DWARF EH or something.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple">
<p class="MsoNormal">* Add support to generate stack-based EH tables for 32-bit targets.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I haven’t seen any work on this. Am I correct in thinking that other than the placement of the EH tables the 32-bit implementation will be able to re-use all of the other SEH code (IR generation, outlining, etc.)?</p></div></blockquote><div><br></div><div>Yep, this should be all backend work at this point.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div>
<p class="MsoNormal">* Add more tests.<u></u><u></u></p>
<p class="MsoNormal"><u></u><br></p>
<p class="MsoNormal">C++ Exception Handling<u></u><u></u></p>
<p class="MsoNormal">-------------------------------<u></u><u></u></p>
<p class="MsoNormal">* Add support for MSVC-specific try-except IR emission to clang.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">This seems fairly straight-forward. I saw some code in your D5607 review to add a way to access the correct personality function. Other than that, it looks like this will just be a matter of removing the “ErrorUnspported” blocks and adding
MSVC-specific support to the parts of the code that are currently generating libc++abi calls for throwing and catching exceptions. The general shape of the IR generated seems to be correct.</p></div></div></blockquote><div><br></div><div>Yep, I want to use the same basic IR form.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal"><u></u></p>
<p class="MsoNormal">* Add support for outlining C++ catch handlers<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">This will be very similar to the filter outlining in the D6556 review. I think a bit of extra effort will be required to correctly identify and group cleanup handlers and get them mixed with the exception handlers correctly, but overall
I feel like I have a handle on this.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">* Add support to emit .xdata table for C++EH for 64-bit targets.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">The analogous SEH code should provide a stable location for where these changes need to be made. From there it seems to be a matter of plumbing to get the handler addresses and new code to emit the table in the correct format for the MSVC
C++ personality function.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">* Add support to generate stack-based C++EH tables for 32-bit targets<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">* Add more tests<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">------------------------------------------------<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I think I’ve mentioned before that C++ exception handling is my main interest here. I’ve been planning to follow through on the remaining work for the function outlining for both SEH and C++EH. Beyond that, I guess we need to talk about
what work you’ve already got in flight. Would you want me to work on the other C++EH tasks while you finish up SEH, or is there something there that overlaps with work you’ve already started?</p></div></div></blockquote><div><br></div><div>Yeah, I think C++ EH would be a good task to split off here. Emitting the 64-bit C++ EH tables is probably a good first step, but it would be really good if we can start landing patches and iterating...</div></div></div></div>