[AST] Initialized data after TypeSourceInfo

[vitalybuka]

Summary

There is no initialization of the data between allocation
and first getBeginLoc call.

allocation: llvm-project/clang/lib/AST/ASTContext.cpp:3022
use: llvm-project/clang/lib/AST/TypeLoc.cpp:222

Msan report https://reviews.llvm.org/P8306

[vitalybuka]

use 0

[rjmccall]

This memory is supposed to be initialized when we copy the TypeLoc. Are you observing that not happening?

[vitalybuka]

In D150499#4341115, @rjmccall wrote:

This memory is supposed to be initialized when we copy the TypeLoc. Are you observing that not happening?

Yes. There is the msan report in the description.

[vitalybuka]

ping, any concerns regarding this patch?
i want to make MSAN stricter on our bot by reducing -O level

[vitalybuka]

ping

[vitalybuka]

Oh, I rerun msan bot locally and it looked like issue dissipated, but I probably checked wrong logs.
So I enabled -Oz on the bot, to catch more bugs, but the issue is still there https://lab.llvm.org/buildbot/#/builders/5/builds/33926

Let's land this trivial fix, and if owners of the AST believe the root-cause is different, we can investigate later.

clang/include/clang/AST/Type.h

 /// @endcode
 class alignas(8) TypeSourceInfo {
   // Contains a memory block after the class, used for type source information,
   // allocated by ASTContext.
   friend class ASTContext;
 
   QualType Ty;
 
-  TypeSourceInfo(QualType ty) : Ty(ty) {}
+  TypeSourceInfo(QualType ty, size_t DataSize); // implemented in TypeLoc.h
 
 public:
   /// Return the type wrapped by this type source info.
   QualType getType() const { return Ty; }
 
   /// Return the TypeLoc wrapper for the type source info.
   TypeLoc getTypeLoc() const; // implemented in TypeLoc.h
 

clang/include/clang/AST/TypeLoc.h

private:
 
   static void initializeImpl(ASTContext &Context, TypeLoc TL,
                              SourceLocation Loc);
   static TypeLoc getNextTypeLocImpl(TypeLoc TL);
   static TypeLoc IgnoreParensImpl(TypeLoc TL);
   static SourceRange getLocalSourceRangeImpl(TypeLoc TL);
 };
 
+inline TypeSourceInfo::TypeSourceInfo(QualType ty, size_t DataSize) : Ty(ty) {
+  // Init data attached to the object. See getTypeLoc.
+  memset(this + 1, 0, DataSize);
+}
+
 /// Return the TypeLoc for a type source info.
 inline TypeLoc TypeSourceInfo::getTypeLoc() const {
   // TODO: is this alignment already sufficient?
   return TypeLoc(Ty, const_cast<void*>(static_cast<const void*>(this + 1)));
 }
 
 /// Wrapper of type source information for a type with
 /// no direct qualifiers.

clang/lib/AST/ASTContext.cpp

TypeSourceInfo *ASTContext::CreateTypeSourceInfo(QualType T,
   if (!DataSize)
     DataSize = TypeLoc::getFullDataSizeForType(T);
   else
     assert(DataSize == TypeLoc::getFullDataSizeForType(T) &&
            "incorrect data size provided to CreateTypeSourceInfo!");
 
   auto *TInfo =
     (TypeSourceInfo*)BumpAlloc.Allocate(sizeof(TypeSourceInfo) + DataSize, 8);
-  new (TInfo) TypeSourceInfo(T);
+  new (TInfo) TypeSourceInfo(T, DataSize);
   return TInfo;
 }
 
 TypeSourceInfo *ASTContext::getTrivialTypeSourceInfo(QualType T,
                                                      SourceLocation L) const {
   TypeSourceInfo *DI = CreateTypeSourceInfo(T);
   DI->getTypeLoc().initialize(const_cast<ASTContext &>(*this), L);
   return DI;