Trying to fix Mangler memory leak in TargetLoweringObjectFile.

[ioeric]

Summary

TargetLoweringObjectFile can be re-used and thus TargetLoweringObjectFile::Initialize()
can be called multiple times causing Mang pointer memory leak.

[ioeric]

Since this is blocking our internal integration, I will commit it now. Please re-open this if there is any problem.

include/llvm/Target/TargetLoweringObjectFile.h

namespace llvm {
   class ConstantExpr;
   class GlobalValue;
   class TargetMachine;
 
 class TargetLoweringObjectFile : public MCObjectFileInfo {
   MCContext *Ctx;
 
   /// Name-mangler for global names.
-  Mangler *Mang;
+  Mangler *Mang = nullptr;
 
   TargetLoweringObjectFile(
     const TargetLoweringObjectFile&) = delete;
   void operator=(const TargetLoweringObjectFile&) = delete;
 
 protected:
   bool SupportIndirectSymViaGOTPCRel;
   bool SupportGOTPCRelWithOffset;

lib/Target/TargetLoweringObjectFile.cpp

 //===----------------------------------------------------------------------===//
 
 /// Initialize - this method must be called before any actual lowering is
 /// done.  This specifies the current context for codegen, and gives the
 /// lowering implementations a chance to set up their default sections.
 void TargetLoweringObjectFile::Initialize(MCContext &ctx,
                                           const TargetMachine &TM) {
   Ctx = &ctx;
+  // `Initialize` can be called more than once.
+  if (Mang != nullptr) delete Mang;
   Mang = new Mangler();
   InitMCObjectFileInfo(TM.getTargetTriple(), TM.isPositionIndependent(),
                        TM.getCodeModel(), *Ctx);
 }
 
 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
   delete Mang;
 }