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IR: Drop metadata references more aggressively during teardown

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Sometimes teardown happens before the debug info graph is complete
(e.g., when clang throws an error).  In that case, `MDNode`s will still
have RAUW, so deleting constants that the `MDNode`s point at will be
relatively expensive -- it'll cause re-uniquing all up the chain (what
I've been referring to as "teardown madness").

So, drop references *before* deleting constants.  We need to drop a few
more references now: the metadata side of the metadata/value bridges
needs to be dropped off the cliff along with the rest of it (previously,
the bridges were cleaned before we did anything with the `MDNode`s).

There's no real functionality change here -- state before and after
`LLVMContextImpl::~LLVMContextImpl()` is unchanged -- so no testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226044 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2015-01-14 21:58:17 +00:00
parent 33f5127540
commit 0294f639d2
2 changed files with 32 additions and 16 deletions
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8
include/llvm/IR/Metadata.h
View File

@ -115,6 +115,9 @@ class MetadataAsValue : public Value {
MetadataAsValue(Type *Ty, Metadata *MD);
~MetadataAsValue();
/// \brief Drop use of metadata (during teardown).
void dropUse() { MD = nullptr; }
public:
static MetadataAsValue *get(LLVMContext &Context, Metadata *MD);
static MetadataAsValue *getIfExists(LLVMContext &Context, Metadata *MD);
@ -185,6 +188,11 @@ class ValueAsMetadata : public Metadata, ReplaceableMetadataImpl {
Value *V;
/// \brief Drop users without RAUW (during teardown).
void dropUsers() {
ReplaceableMetadataImpl::resolveAllUses(/* ResolveUsers */ false);
}
protected:
ValueAsMetadata(unsigned ID, Value *V)
: Metadata(ID), V(V) {

40
lib/IR/LLVMContextImpl.cpp
View File

@ -72,7 +72,30 @@ LLVMContextImpl::~LLVMContextImpl() {
// the container. Avoid iterators during this operation:
while (!OwnedModules.empty())
delete *OwnedModules.begin();
// Drop references for MDNodes. Do this before Values get deleted to avoid
// unnecessary RAUW when nodes are still unresolved.
for (auto *I : DistinctMDNodes)
I->dropAllReferences();
for (auto *I : MDTuples)
I->dropAllReferences();
for (auto *I : MDLocations)
I->dropAllReferences();
// Also drop references that come from the Value bridges.
for (auto &Pair : ValuesAsMetadata)
Pair.second->dropUsers();
for (auto &Pair : MetadataAsValues)
Pair.second->dropUse();
// Destroy MDNodes.
for (UniquableMDNode *I : DistinctMDNodes)
I->deleteAsSubclass();
for (MDTuple *I : MDTuples)
delete I;
for (MDLocation *I : MDLocations)
delete I;
// Free the constants. This is important to do here to ensure that they are
// freed before the LeakDetector is torn down.
std::for_each(ExprConstants.map_begin(), ExprConstants.map_end(),
@ -135,21 +158,6 @@ LLVMContextImpl::~LLVMContextImpl() {
for (auto &Pair : ValuesAsMetadata)
delete Pair.second;
// Destroy MDNodes.
for (auto *I : DistinctMDNodes)
I->dropAllReferences();
for (auto *I : MDTuples)
I->dropAllReferences();
for (auto *I : MDLocations)
I->dropAllReferences();
for (UniquableMDNode *I : DistinctMDNodes)
I->deleteAsSubclass();
for (MDTuple *I : MDTuples)
delete I;
for (MDLocation *I : MDLocations)
delete I;
// Destroy MDStrings.
MDStringCache.clear();
}