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

[Philip Reames]

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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