[PATCH] D128955: [WPD] Use new llvm.public.type.test intrinsic for potentially publicly visible classes

[Teresa Johnson via Phabricator via llvm-commits]

tejohnson added inline comments.


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Comment at: clang/test/CodeGenCXX/thinlto-distributed-type-metadata.cpp:22
 // OPT-NOT: @llvm.type.test
-// OPT-NOT: call void @llvm.assume
 // We should have only one @llvm.assume call, the one that was expanded
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aeubanks wrote:
> tejohnson wrote:
> > Why remove this one here and below?
> we end up RAUWing the `public.type.test` with true and end up with `assume(true)` which is harmless and gets removed by something like instcombine
Sure, but it should still be gone and can confirm that here? If it isn't useful to check for, then the comment should probably be changed too since it mentions assumes.


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Comment at: clang/test/CodeGenCXX/thinlto_public_type_test_distributed.ll:23
+; RUN:   -o %t.native.o -x ir %t.o --save-temps=obj
+; RUN: llvm-dis %t.native.o.1.promote.bc -o - | FileCheck %s --check-prefix=HIDDEN
+
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Is there a reason why the hidden version checks after promote but the public version above checks after importing?


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Comment at: clang/test/CodeGenCXX/type-metadata.cpp:212
   // CFI-NVT-NOT: call i1 @llvm.type.test
-  // CFI-VT: [[P:%[^ ]*]] = call i1 @llvm.type.test
+  // CFI-VT-ITANIUM: [[P:%[^ ]*]] = call i1 @llvm.type.test
+  // CFI-VT-MS: [[P:%[^ ]*]] = call i1 @llvm.type.test
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Is the CFI-VT-ITANIUM and CFI-VT-MS split needed? I don't see any differences in their checking. Can we go back to just a single CFI-VT here?


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Comment at: lld/test/ELF/lto/update_public_type_test.ll:1
+; REQUIRES: x86
+
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aeubanks wrote:
> tejohnson wrote:
> > Add comments about what is being tested. Also good to test via llvm-lto2 which has a similar -whole-program-visibility option, rather than just via lld here. See for example llvm/test/ThinLTO/X86/devirt_vcall_vis_public.ll.
> added comments
> 
> I extended llvm/test/ThinLTO/X86/devirt_vcall_vis_public.ll, is that ok?
Yeah sure that's fine. But maybe also add a direct check there in both cases after promote that the public.type.test/assume were transformed as expected as you do in this test.


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Comment at: llvm/lib/Analysis/ModuleSummaryAnalysis.cpp:169
+  case Intrinsic::public_type_test: {
+    // errs() << "HIHI " << CI->getParent()->getParent()->getName() <<"\n";
+    // CI->dump();
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Remove commented debugging code here and below


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Comment at: llvm/lib/LTO/LTO.cpp:1106
                                 DynamicExportSymbols);
+  updatePublicTypeTestCalls(*RegularLTO.CombinedModule,
+                            Conf.HasWholeProgramVisibility);
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Probably need to do for the legacy LTO API as well, which also calls  updateVCallVisibilityInModule (LTOCodeGenerator.cpp). This is used both some other linkers such as ld64. Otherwise I think the public.type.test intrinsics will never get converted for those LTO users, leading to errors probably? You can test the legacy LTO via llvm-lto (e.g. see tests in llvm/test/LTO/X86).


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Comment at: llvm/lib/LTO/LTOBackend.cpp:565
+  updatePublicTypeTestCalls(Mod,
+                            Conf.HasWholeProgramVisibility ||
+                                CombinedIndex.withWholeProgramVisibility());
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Can we just check the combined index flag now?


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Comment at: llvm/lib/LTO/LTOBackend.cpp:595
 
+  updatePublicTypeTestCalls(Mod, Conf.HasWholeProgramVisibility);
+
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aeubanks wrote:
> tejohnson wrote:
> > aeubanks wrote:
> > > I'm not sure where the best place to put these is
> > I don't think that this will work for distributed ThinLTO, where the ThinLTO Backends are run via clang, which isn't going to have this config variable set (since it is set only during LTO linking). I think something may need to be recorded in the index as a flag there at thin link / indexing time that can be checked here.
> > 
> > It would then be nice to consolidate this handling into WPD itself, e.g. at the start of DevirtModule::run, but unfortunately we won't have a summary index for pure regular LTO WPD so I don't think that would work. So in here is ok but I would do it early to handle some of the early return cases.
> > 
> > (Please add a distributed ThinLTO test too)
> Added a distributed ThinLTO test: clang/test/CodeGenCXX/thinlto_public_type_test_distributed.ll.
> 
> I added `ModuleSummaryIndex::WithWholeProgramVisibility` but I'm not sure where I'd set it, and that's causing the test to fail.
I see from your most recent update that you added code to set/check this new index flag. But I think you would want to set it around the same place where we update the vcall visibility during the thin link (see calls to updateVCallVisibilityInIndex). And I would do it via a new method in the WPD source file that uses the existing hasWholeProgramVisibility() that checks the OR of the config flag or the internal option. Then you don't need to add a new flag to llvm-lto2 for this purpose.

Also, as I noted for the regular LTO handling elsewhere, I think you need to add similar handling for the legacy LTO implementation. See other callers to updateVCallVisibilityInIndex.


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Comment at: llvm/lib/Transforms/IPO/LowerTypeTests.cpp:1849
+      dropTypeTests(M, *TypeTestFunc);
+    Function *PublicTypeTestFunc =
+        M.getFunction(Intrinsic::getName(Intrinsic::public_type_test));
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aeubanks wrote:
> tejohnson wrote:
> > Shouldn't we have converted all of these by now?
> Hmm, I vaguely remember adding this because some clang test failed (something to do with the extra LTT we add in BackendUtil.cpp), but reverting this doesn't cause any failures.
Related to some of my other comments about ensuring we do the conversion for the legacy LTO interfaces, perhaps this we should assert here if there are any remaining public.type.test intrinsics? Not sure what the failure mode is if any of those stick around otherwise.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128955/new/

https://reviews.llvm.org/D128955