SIL: Let SILGlobalVariables be destroyed.

This fixes a memory leak: instructions of the static initializer block were not be freed.

rdar://problem/66931238

Author: eeckstein

include/swift/SIL/SILBasicBlock.h

@@ -76,6 +76,9 @@ public llvm::ilist_node<SILBasicBlock>, public SILAllocated<SILBasicBlock> {
   /// This method unlinks 'self' from the containing SILFunction and deletes it.
   void eraseFromParent();
 
+  /// Remove all instructions of a SILGlobalVariable's static initializer block.
+  void clearStaticInitializerBlock(SILModule &module);
+
   //===--------------------------------------------------------------------===//
   // SILInstruction List Inspection and Manipulation
   //===--------------------------------------------------------------------===//

include/swift/SIL/SILGlobalVariable.h

@@ -233,7 +233,7 @@ public ilist_node_traits<::swift::SILGlobalVariable> {
   using SILGlobalVariable = ::swift::SILGlobalVariable;
 
 public:
-  static void deleteNode(SILGlobalVariable *V) {}
+  static void deleteNode(SILGlobalVariable *V) { V->~SILGlobalVariable(); }
 
 private:
   void createNode(const SILGlobalVariable &);

lib/SIL/IR/SILBasicBlock.cpp

@@ -43,30 +43,43 @@ SILBasicBlock::SILBasicBlock(SILFunction *parent, SILBasicBlock *relativeToBB,
   }
 }
 SILBasicBlock::~SILBasicBlock() {
+  if (!getParent()) {
+    assert(ArgumentList.empty() &&
+           "a static initializer block must not have arguments");
+    assert(InstList.empty() &&
+           "a static initializer block must be cleared before the destructor");
+    return;
+  }
+    
+  SILModule &M = getModule();
+
   // Invalidate all of the basic block arguments.
   for (auto *Arg : ArgumentList) {
-    getModule().notifyDeleteHandlers(Arg);
+    M.notifyDeleteHandlers(Arg);
   }
 
   dropAllReferences();
 
-  SILModule *M = nullptr;
-  if (getParent())
-    M = &getParent()->getModule();
-
   for (auto I = begin(), E = end(); I != E;) {
     auto Inst = &*I;
     ++I;
-    if (M) {
-      // Notify the delete handlers that the instructions in this block are
-      // being deleted.
-      M->notifyDeleteHandlers(Inst);
-    }
     erase(Inst);
   }
+  assert(InstList.empty());
+}
+
+void SILBasicBlock::clearStaticInitializerBlock(SILModule &module) {
+  assert(!getParent() && "not a global variable's static initializer block");
+  assert(ArgumentList.empty() &&
+         "a static initializer block must not have arguments");
 
-  // iplist's destructor is going to destroy the InstList.
-  InstList.clearAndLeakNodesUnsafely();
+  for (auto I = begin(), E = end(); I != E;) {
+    SILInstruction *Inst = &*I;
+    ++I;
+    InstList.erase(Inst);
+    module.deallocateInst(Inst);
+  }
+  assert(InstList.empty());
 }
 
 int SILBasicBlock::getDebugID() const {

lib/SIL/IR/SILGlobalVariable.cpp

@@ -58,7 +58,8 @@ SILGlobalVariable::SILGlobalVariable(SILModule &Module, SILLinkage Linkage,
 }
 
 SILGlobalVariable::~SILGlobalVariable() {
-  getModule().GlobalVariableMap.erase(Name);
+  StaticInitializerBlock.dropAllReferences();
+  StaticInitializerBlock.clearStaticInitializerBlock(Module);
 }
 
 /// Get this global variable's fragile attribute.