[MSan] Disable sanitization for __sanitizer_dtor_callback.

[morehouse]

Summary

Eliminate unnecessary instrumentation at __sanitizer_dtor_callback
call sites. Fixes https://github.com/google/sanitizers/issues/861.

[eugenis]

A test, please.

clang/lib/CodeGen/CGClass.cpp

1592

Use SanitizerScope.

[morehouse]

• Add test case.
• Use SanitizerScope.

[eugenis]

Please also add a tiny LLVM test that call instructions with nosanitize metadata are not instrumented.

[morehouse]

• Add LLVM test.

clang/lib/CodeGen/CGClass.cpp

llvm::Value *Args[] = {CGF.Builder.CreateBitCast(Ptr, CGF.VoidPtrTy),
                           llvm::ConstantInt::get(CGF.SizeTy, PoisonSize)};
 
    llvm::Type *ArgTypes[] = {CGF.VoidPtrTy, CGF.SizeTy};
 
    llvm::FunctionType *FnType =
        llvm::FunctionType::get(CGF.VoidTy, ArgTypes, false);
    llvm::Value *Fn =
        CGF.CGM.CreateRuntimeFunction(FnType, "__sanitizer_dtor_callback");
-   CGF.EmitNounwindRuntimeCall(Fn, Args);
+   llvm::CallInst *I = CGF.EmitNounwindRuntimeCall(Fn, Args);
+   I->setMetadata("nosanitize", llvm::MDNode::get(CGF.getLLVMContext(),
+                                                  llvm::None));
  }
 
   class SanitizeDtorMembers final : public EHScopeStack::Cleanup {
     const CXXDestructorDecl *Dtor;
 
   public:
     SanitizeDtorMembers(const CXXDestructorDecl *Dtor) : Dtor(Dtor) {}
 

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

default:
       if (!handleUnknownIntrinsic(I))
         visitInstruction(I);
       break;
     }
   }
 
   void visitCallSite(CallSite CS) {
     Instruction &I = *CS.getInstruction();
+    if (I.getMetadata("nosanitize")) return;
     assert((CS.isCall() || CS.isInvoke()) && "Unknown type of CallSite");
     if (CS.isCall()) {
       CallInst *Call = cast<CallInst>(&I);
 
       // For inline asm, do the usual thing: check argument shadow and mark all
       // outputs as clean. Note that any side effects of the inline asm that are
       // not immediately visible in its constraints are not handled.
       if (Call->isInlineAsm()) {