r356598 - Recommit "Support attribute used in member funcs of class templates"

[Rafael Auler via cfe-commits]

I’m familiar with this issue as I had to fix a memory bug in LLVM IRLinker that was exposed by this commit. That’s why I initially reverted it. However, after fixing it, I was able to do the full clang LTO self-hosting with lld on Linux. Is there any way I can repro this issue? It’s probably a bad interaction of attribute used and an optimization. See https://reviews.llvm.org/D59552


From: Michael Spencer <bigcheesegs at gmail.com>
Date: Tuesday, March 26, 2019 at 6:59 PM
To: Rafael Auler <rafaelauler at fb.com>
Cc: "cfe-commits at lists.llvm.org" <cfe-commits at lists.llvm.org>
Subject: Re: r356598 - Recommit "Support attribute used in member funcs of class templates"

On Wed, Mar 20, 2019 at 12:21 PM Rafael Auler via cfe-commits <cfe-commits at lists.llvm.org<mailto:cfe-commits at lists.llvm.org>> wrote:
Author: rafauler
Date: Wed Mar 20 12:22:24 2019
New Revision: 356598

URL: http://llvm.org/viewvc/llvm-project?rev=356598&view=rev<https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D356598-26view-3Drev&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kx31RNFp5lAJejEYwuEQ4Zc5A6GakBit07EY08bIAvc&m=Tp8AU6vZlFhDRTWeUHWkXzTHsspDHfWnErBtktRStLc&s=z5t_fduYusJn1DP4wsOLj9KYsPpKMyUkVXk2JAPRNM8&e=>
Log:
Recommit "Support attribute used in member funcs of class templates"

This diff previously exposed a bug in LLVM's IRLinker, breaking
buildbots that tried to self-host LLVM with monolithic LTO.
The bug is now in LLVM by D59552

Original commit message:
As PR17480 describes, clang does not support the used attribute
for member functions of class templates. This means that if the member
function is not used, its definition is never instantiated. This patch
changes clang to emit the definition if it has the used attribute.

Test Plan: Added a testcase

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D56928<https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D56928&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kx31RNFp5lAJejEYwuEQ4Zc5A6GakBit07EY08bIAvc&m=Tp8AU6vZlFhDRTWeUHWkXzTHsspDHfWnErBtktRStLc&s=Y54Z_weCYOa7tU_wNo9M6yMwDeLwDQKoNdrnZu_PllE&e=>

Added:
    cfe/trunk/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp
Modified:
    cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp

Modified: cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp?rev=356598&r1=356597&r2=356598&view=diff<https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_cfe_trunk_lib_Sema_SemaTemplateInstantiateDecl.cpp-3Frev-3D356598-26r1-3D356597-26r2-3D356598-26view-3Ddiff&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kx31RNFp5lAJejEYwuEQ4Zc5A6GakBit07EY08bIAvc&m=Tp8AU6vZlFhDRTWeUHWkXzTHsspDHfWnErBtktRStLc&s=Zh4mt8nrN7qZNDUMeoVkSQtZ2ebQTgXi_MOQa87S5fY&e=>
==============================================================================
--- cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaTemplateInstantiateDecl.cpp Wed Mar 20 12:22:24 2019
@@ -2232,6 +2232,20 @@ TemplateDeclInstantiator::VisitCXXMethod
     Owner->addDecl(Method);
   }

+  // PR17480: Honor the used attribute to instantiate member function
+  // definitions
+  if (Method->hasAttr<UsedAttr>()) {
+    if (const auto *A = dyn_cast<CXXRecordDecl>(Owner)) {
+      SourceLocation Loc;
+      if (const MemberSpecializationInfo *MSInfo =
+              A->getMemberSpecializationInfo())
+        Loc = MSInfo->getPointOfInstantiation();
+      else if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(A))
+        Loc = Spec->getPointOfInstantiation();
+      SemaRef.MarkFunctionReferenced(Loc, Method);
+    }
+  }
+
   return Method;
 }


Added: cfe/trunk/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp?rev=356598&view=auto<https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_cfe_trunk_test_CodeGenCXX_attr-2Dused-2Dmember-2Dfunction-2Dimplicit-2Dinstantiation.cpp-3Frev-3D356598-26view-3Dauto&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kx31RNFp5lAJejEYwuEQ4Zc5A6GakBit07EY08bIAvc&m=Tp8AU6vZlFhDRTWeUHWkXzTHsspDHfWnErBtktRStLc&s=CMIrOdMDTKRq5dy52CT5B9v2iMMA2dPslSvyhjaCb2o&e=>
==============================================================================
--- cfe/trunk/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp (added)
+++ cfe/trunk/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp Wed Mar 20 12:22:24 2019
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+// Check that PR17480 is fixed: __attribute__((used)) ignored in templated
+// classes
+namespace InstantiateUsedMemberDefinition {
+template <typename T>
+struct S {
+  int __attribute__((used)) f() {
+    return 0;
+  }
+};
+
+void test() {
+  // Check that InstantiateUsedMemberDefinition::S<int>::f() is defined
+  // as a result of the S class template implicit instantiation
+  // CHECK: define linkonce_odr i32 @_ZN31InstantiateUsedMemberDefinition1SIiE1fEv
+  S<int> inst;
+}
+} // namespace InstantiateUsedMemberDefinition

I believe this commit broke our (Apple) internal LTO bots.  I'm working on getting more information and narrowing it down.  The symptom is:



Undefined symbols for architecture x86_64:

  "llvm::cfg::Update<llvm::BasicBlock*>::dump() const", referenced from:

      DominatorTreeBatchUpdates_LegalizeDomUpdates_Test::TestBody() in DominatorTreeBatchUpdatesTest.cpp.o

      DominatorTreeBatchUpdates_LegalizePostDomUpdates_Test::TestBody() in DominatorTreeBatchUpdatesTest.cpp.o



Has anyone else seen a similar issue with this commit?
- Michael Spencer
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