<div dir="ltr">I went ahead and implemented @llvm.frameallocate in a patch here: <a href="http://reviews.llvm.org/D6493" target="_blank">http://reviews.llvm.org/D6493</a><div><br></div><div>Andrew, do you have a wip patch for outlining, or any lessons learned from attempting it? I think outlining is now the next step, so let me know if there's something you're actively working on so I can avoid duplicated effort. :)</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Nov 25, 2014 at 3:09 PM, Kaylor, Andrew <span dir="ltr"><<a href="mailto:andrew.kaylor@intel.com" target="_blank">andrew.kaylor@intel.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal">> 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:<u></u><u></u></p>
</span><p class="MsoNormal">…<u></u><u></u></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">That sounds like a good starting point.<u></u><u></u></span></p><span class="">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal">> Chandler expressed strong concerns about this design, however, as @llvm.eh.get_capture_block adds an ordering constraint on CodeGen. Once you add this intrinsic, we *have* to do frame layout of @_Z13do_some_thingRi *before* we can emit
code for all the callers of @llvm.eh.get_capture_block. Today, this is easy, because module order defines emission order, but in the great glorious future, codegen will hopefully be parallelized, and then we've inflicted this horrible constraint on the innocent.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">> His suggestion to break the ordering dependence was to lock down the frame offset of the capture block to always be some fixed offset known by the target (ie ebp - 4 on x86, if we like that).<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
</span><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Chandler probably has a better feel for this sort of thing than I do. I can’t think of a reason offhand why that wouldn’t work, but it makes me a little nervous.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">What would that look like in the IR? Would we use the same intrinsics and just lower them to use the known location?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I’ll think about this, but for now I’m happy to just proceed with the belief that it’s a solvable problem either way.<u></u><u></u></span></p><span class="">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">>> For C++ exception handling, we need cleanup code that executes before the catch handlers and cleanup
code that excutes in the case on uncaught exceptions. I think both of these need to be outlined for the MSVC environment. Do you think we need a stub handler to be inserted in cases where no actual cleanup is performed?</span><span style="color:black"><u></u><u></u></span></p>
<p class="MsoNormal">> I think it's actually harder than that, once you consider nested trys:<u></u><u></u></p>
<p class="MsoNormal">> void f() {<u></u><u></u></p>
<p class="MsoNormal">> try {<u></u><u></u></p>
<p class="MsoNormal">> Outer outer;<u></u><u></u></p>
<p class="MsoNormal">> try {<u></u><u></u></p>
<p class="MsoNormal">> Inner inner;<u></u><u></u></p>
<p class="MsoNormal">> g();<u></u><u></u></p>
<p class="MsoNormal">> } catch (int) {<u></u><u></u></p>
<p class="MsoNormal">> // ~Inner gets run first<br>
> }<u></u><u></u></p>
<p class="MsoNormal">> } catch (float) {<u></u><u></u></p>
<p class="MsoNormal">> // ~Inner gets run first<u></u><u></u></p>
<p class="MsoNormal">> // ~Outer gets run next<br>
> }<u></u><u></u></p>
<p class="MsoNormal">> // uncaught exception? Run ~Inner then ~Outer.<br>
> }<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
</span><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I took a look at the IR that’s generated for this example. I see what you mean. So there is potentially cleanup code before and after every catch handler,
right?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Do you happen to know offhand what that looks like in the .xdata for the _CxxFrameHandler3 function?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">-Andy<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p>
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