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IR: Fix a use-after-free in RAUW

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Happened pretty commonly during `LLVMContext` teardown when `clang -g`
hit an error.  This fixes the use-after-free.  Next I'll clean up
teardown so that it's not RAUW'ing when metadata-tracked values are
deleted (only really causes a problem if the graph is mid-construction
when teardown starts, but it's still unnecessary work).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226029 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2015-01-14 19:56:10 +00:00
parent 9ea8dfef83
commit 9e4a11f46c
2 changed files with 33 additions and 0 deletions
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5
lib/IR/Metadata.cpp
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@ -167,6 +167,11 @@ void ReplaceableMetadataImpl::replaceAllUsesWith(Metadata *MD) {
return L.second.second < R.second.second;
});
for (const auto &Pair : Uses) {
// Check that this Ref hasn't disappeared after RAUW (when updating a
// previous Ref).
if (!UseMap.count(Pair.first))
continue;
OwnerTy Owner = Pair.second.first;
if (!Owner) {
// Update unowned tracking references directly.

28
unittests/IR/MetadataTest.cpp
View File

@ -484,6 +484,34 @@ TEST_F(ValueAsMetadataTest, UpdatesOnRAUW) {
EXPECT_TRUE(MD->getValue() == GV1.get());
}
TEST_F(ValueAsMetadataTest, CollidingDoubleUpdates) {
// Create a constant.
ConstantAsMetadata *CI = ConstantAsMetadata::get(
ConstantInt::get(getGlobalContext(), APInt(8, 0)));
// Create a temporary to prevent nodes from resolving.
std::unique_ptr<MDNodeFwdDecl> Temp(MDNode::getTemporary(Context, None));
// When the first operand of N1 gets reset to nullptr, it'll collide with N2.
Metadata *Ops1[] = {CI, CI, Temp.get()};
Metadata *Ops2[] = {nullptr, CI, Temp.get()};
auto *N1 = MDTuple::get(Context, Ops1);
auto *N2 = MDTuple::get(Context, Ops2);
ASSERT_NE(N1, N2);
// Tell metadata that the constant is getting deleted.
//
// After this, N1 will be invalid, so don't touch it.
ValueAsMetadata::handleDeletion(CI->getValue());
EXPECT_EQ(nullptr, N2->getOperand(0));
EXPECT_EQ(nullptr, N2->getOperand(1));
EXPECT_EQ(Temp.get(), N2->getOperand(2));
// Clean up Temp for teardown.
Temp->replaceAllUsesWith(nullptr);
}
typedef MetadataTest TrackingMDRefTest;
TEST_F(TrackingMDRefTest, UpdatesOnRAUW) {