commit e16d58751510fe3eefa95d0fbb6ec5f2cc4bc63f
author Duncan P. N. Exon Smith <dexonsmith@apple.com> Wed Jan 14 21:58:17 2015 +0000
committer Duncan P. N. Exon Smith <dexonsmith@apple.com> Wed Jan 14 21:58:17 2015 +0000
tree 39a3bd4801e4f365f26c727f59d893725a1cf6ac
parent e5f997e551f62cbaa88333259c4d8f0c9272207f

IR: Drop metadata references more aggressively during teardown

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.

llvm-svn: 226044

llvm/lib/IR/LLVMContextImpl.cpp

diff --git a/llvm/lib/IR/LLVMContextImpl.cpp b/llvm/lib/IR/LLVMContextImpl.cpp
index 1fa080b..01a0e6c 100644
--- a/llvm/lib/IR/LLVMContextImpl.cpp
+++ b/llvm/lib/IR/LLVMContextImpl.cpp
@@ -72,7 +72,30 @@
   // 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 @@
   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();
 }