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<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:11.0pt;font-family:Wingdings;color:#1F497D"><span style="mso-list:Ignore">Ø<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:black">Some Clang tests match the bitcode that's being emitted, but the emitted sometimes differs between the legacy and new pass manager.</span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I didn’t think all passes were setup to run with the new PM, or if they were, they didn’t necessarily run in the same order as with the old PM. You’d certainly
see different IR and break tests.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> cfe-dev <cfe-dev-bounces@lists.llvm.org>
<b>On Behalf Of </b>Reid Kleckner via cfe-dev<br>
<b>Sent:</b> Thursday, February 14, 2019 4:29 PM<br>
<b>To:</b> Petr Hosek <phosek@chromium.org>; Chandler Carruth <chandlerc@google.com><br>
<b>Cc:</b> CFE Dev <cfe-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [cfe-dev] Clang tests with new pass manager<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Why does the new PM always make the target machine available? That seems inconsistent with our past directions. We go to all this trouble to make datalayout encapsulate everything IR-level passes need to know about the target (and TLI,
I guess), we have the triple, metadata for wchar_t and all this stuff... and then we just let IR passes talk to the Target?<br>
<br>
I think it would be a shame to lose the ability to run opt and clang -S -emit-llvm for a target without compiling in the target's code generator.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Feb 13, 2019 at 6:08 PM Petr Hosek via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">I've been experimenting with enabling the new PM by default in our toolchain, using the <span style="color:black">-DENABLE_EXPERIMENTAL_NEW_PASS_MANAGER=ON option. However, when I do that, I see a lot (498) of failing tests.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="color:black">I've filed PR40724 for this issue and after a bit of investigating I also found out why these tests are failing. It boils down to two issues:</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="color:black">1. Unlike the legacy pass manager, the new pass manager always makes the target machine available to passes so we have to always instantiate it even when we're only emitting bitcode, see
</span><a href="https://github.com/llvm/llvm-project/blob/master/clang/lib/CodeGen/BackendUtil.cpp#L952" target="_blank">https://github.com/llvm/llvm-project/blob/master/clang/lib/CodeGen/BackendUtil.cpp#L952</a><span style="color:black">. This breaks when
some targets tested by Clang don't match targets built by LLVM. In our case this is more prominent because we disable all targets that we don't support in our toolchain, but even in the default configuration you'll still see failures for experimental targets
(e.g. RISC-V).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">2. Some Clang tests match the bitcode that's being emitted, but the emitted sometimes differs between the legacy and new pass manager.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Has anyone already been thinking on how to handle these issues?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">For the first one, the obvious solution is to mark all target-specific tests with appropriate `REQUIRES: <target>-registered-target` conditions. The downside is that we're going to loose coverage for some of the
tests that are being run today with the legacy pass manager even when the target is disabled, but we're already seem to be using these conditions in many Clang tests so maybe it's not a big problem.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">For the second issue, we could set a new feature config in lit whenever new PM is enabled (.e.g experimental-new-pm) and then either mark the broken tests as unsupported under new PM or provide two different bitcode
versions to match against for legacy and new PM. It's probably easiest to start by disabling the failing tests first and then try and update all of them to make them work under new PM.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Do you have any opinion on this or other ideas/suggestions?<o:p></o:p></span></p>
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<p class="MsoNormal">_______________________________________________<br>
cfe-dev mailing list<br>
<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a><br>
<a href="https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" target="_blank">https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a><o:p></o:p></p>
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