[llvm] r224146 - IR: Don't track nullptr on metadata RAUW

[Duncan P. N. Exon Smith]

See: unittests/IR/MetadataTest.cpp

> On 2014 Dec 12, at 14:54, Philip Reames <listmail at philipreames.com> wrote:
> 
> Test case?
> 
> On 12/12/2014 11:24 AM, Duncan P. N. Exon Smith wrote:
>> Author: dexonsmith
>> Date: Fri Dec 12 13:24:33 2014
>> New Revision: 224146
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=224146&view=rev
>> Log:
>> IR: Don't track nullptr on metadata RAUW
>> 
>> The RAUW support in `Metadata` supports going to `nullptr` specifically
>> to handle values being deleted, causing `ValueAsMetadata` to be deleted.
>> 
>> Fix the case where the reference is from a `TrackingMDRef` (as opposed
>> to an `MDOperand` or a `MetadataAsValue`).
>> 
>> This is surprisingly rare -- metadata tracked by `TrackingMDRef` going
>> to null -- but it came up in an openSUSE bootstrap during inlining.  The
>> tracking ref was held by the `ValueMap` because it was referencing a
>> local, the basic block containing the local became dead after it had
>> been merged in, and when the local was deleted, the tracking ref
>> asserted in an `isa`.
>> 
>> Modified:
>>     llvm/trunk/lib/IR/Metadata.cpp
>>     llvm/trunk/unittests/IR/MetadataTest.cpp
>> 
>> Modified: llvm/trunk/lib/IR/Metadata.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Metadata.cpp?rev=224146&r1=224145&r2=224146&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/IR/Metadata.cpp (original)
>> +++ llvm/trunk/lib/IR/Metadata.cpp Fri Dec 12 13:24:33 2014
>> @@ -173,7 +173,8 @@ void ReplaceableMetadataImpl::replaceAll
>>        // Update unowned tracking references directly.
>>        Metadata *&Ref = *static_cast<Metadata **>(Pair.first);
>>        Ref = MD;
>> -      MetadataTracking::track(Ref);
>> +      if (MD)
>> +        MetadataTracking::track(Ref);
>>        UseMap.erase(Pair.first);
>>        continue;
>>      }
>> 
>> Modified: llvm/trunk/unittests/IR/MetadataTest.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/MetadataTest.cpp?rev=224146&r1=224145&r2=224146&view=diff
>> ==============================================================================
>> --- llvm/trunk/unittests/IR/MetadataTest.cpp (original)
>> +++ llvm/trunk/unittests/IR/MetadataTest.cpp Fri Dec 12 13:24:33 2014
>> @@ -207,6 +207,53 @@ TEST_F(MetadataAsValueTest, MDNodeConsta
>>    EXPECT_EQ(V, V2);
>>  }
>>  +typedef MetadataTest ValueAsMetadataTest;
>> +
>> +TEST_F(ValueAsMetadataTest, UpdatesOnRAUW) {
>> +  Type *Ty = Type::getInt1PtrTy(Context);
>> +  std::unique_ptr<GlobalVariable> GV0(
>> +      new GlobalVariable(Ty, false, GlobalValue::ExternalLinkage));
>> +  auto *MD = ValueAsMetadata::get(GV0.get());
>> +  EXPECT_TRUE(MD->getValue() == GV0.get());
>> +  ASSERT_TRUE(GV0->use_empty());
>> +
>> +  std::unique_ptr<GlobalVariable> GV1(
>> +      new GlobalVariable(Ty, false, GlobalValue::ExternalLinkage));
>> +  GV0->replaceAllUsesWith(GV1.get());
>> +  EXPECT_TRUE(MD->getValue() == GV1.get());
>> +}
>> +
>> +typedef MetadataTest TrackingMDRefTest;
>> +
>> +TEST_F(TrackingMDRefTest, UpdatesOnRAUW) {
>> +  Type *Ty = Type::getInt1PtrTy(Context);
>> +  std::unique_ptr<GlobalVariable> GV0(
>> +      new GlobalVariable(Ty, false, GlobalValue::ExternalLinkage));
>> +  TypedTrackingMDRef<ValueAsMetadata> MD(ValueAsMetadata::get(GV0.get()));
>> +  EXPECT_TRUE(MD->getValue() == GV0.get());
>> +  ASSERT_TRUE(GV0->use_empty());
>> +
>> +  std::unique_ptr<GlobalVariable> GV1(
>> +      new GlobalVariable(Ty, false, GlobalValue::ExternalLinkage));
>> +  GV0->replaceAllUsesWith(GV1.get());
>> +  EXPECT_TRUE(MD->getValue() == GV1.get());
>> +
>> +  // Reset it, so we don't inadvertently test deletion.
>> +  MD.reset();
>> +}
>> +
>> +TEST_F(TrackingMDRefTest, UpdatesOnDeletion) {
>> +  Type *Ty = Type::getInt1PtrTy(Context);
>> +  std::unique_ptr<GlobalVariable> GV(
>> +      new GlobalVariable(Ty, false, GlobalValue::ExternalLinkage));
>> +  TypedTrackingMDRef<ValueAsMetadata> MD(ValueAsMetadata::get(GV.get()));
>> +  EXPECT_TRUE(MD->getValue() == GV.get());
>> +  ASSERT_TRUE(GV->use_empty());
>> +
>> +  GV.reset();
>> +  EXPECT_TRUE(!MD);
>> +}
>> +
>>  TEST(NamedMDNodeTest, Search) {
>>    LLVMContext Context;
>>    ConstantAsMetadata *C =
>> 
>> 
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