[ASan] Make GlobalsMD member a const reference

[leonardchan]

Summary

PR42924 points out that copying the GlobalsMetadata type during
construction of AddressSanitizer can result in exteremely lengthened
build times for translation units that have many globals. This can be addressed
by just making the GlobalsMD member in AddressSanitizer a reference to
avoid the copy. The GlobalsMetadata type is already passed to the
constructor as a reference anyway.

[vitalybuka]

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

695

please add const into constructor
ModuleAddressSanitizer(Module &M, const GlobalsMetadata &GlobalsMD,

maybe also pointer, so you can't pass temp object
ModuleAddressSanitizer(Module &M, const GlobalsMetadata *GlobalsMD,

[leonardchan]

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

695

Woops. Sorry, I committed after I got the LGTM but didn't see your comments until later. I committed r373391 which addresses these comments.

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

private:
 
   // These arrays is indexed by AccessIsWrite and Experiment.
   FunctionCallee AsanErrorCallbackSized[2][2];
   FunctionCallee AsanMemoryAccessCallbackSized[2][2];
 
   FunctionCallee AsanMemmove, AsanMemcpy, AsanMemset;
   InlineAsm *EmptyAsm;
   Value *LocalDynamicShadow = nullptr;
-  GlobalsMetadata GlobalsMD;
+  const GlobalsMetadata &GlobalsMD;
   DenseMap<const AllocaInst *, bool> ProcessedAllocas;
 };
 
 class AddressSanitizerLegacyPass : public FunctionPass {
 public:
   static char ID;
 
   explicit AddressSanitizerLegacyPass(bool CompileKernel = false,
private:
   StringRef getGlobalMetadataSection() const;
   void poisonOneInitializer(Function &GlobalInit, GlobalValue *ModuleName);
   void createInitializerPoisonCalls(Module &M, GlobalValue *ModuleName);
   size_t MinRedzoneSizeForGlobal() const {
     return RedzoneSizeForScale(Mapping.Scale);
   }
   int GetAsanVersion(const Module &M) const;
 
-  GlobalsMetadata GlobalsMD;
+  const GlobalsMetadata &GlobalsMD;
   bool CompileKernel;
   bool Recover;
   bool UseGlobalsGC;
   bool UsePrivateAlias;
   bool UseOdrIndicator;
   bool UseCtorComdat;
   Type *IntptrTy;
   LLVMContext *C;