[ms-cxxabi] Add CGCXXABI::NeedsBodylessEmission function.

[pcc]

Summary

This function returns true if the ABI requires that we emit a
definition for a given function, given that we don't have a body
for it in the TU.

[timurrrr]

LGTM for me with one suggestion,

but please note that I'm not an approver for this code, so talk to John for the final review.

lib/CodeGen/CGCXXABI.h

322

Would be nice to give an example of when it's needed, otherwise it's a bit cryptic.

[rnk]

Also, pinging John since this is more interface-y.

lib/CodeGen/CGCXXABI.h

322

"bodyless emission" is confusing to me, but I can't invent a better name. So long as the doc comment explains that this only makes sense when we can do something like delegate to a different variant of the function expected to be emitted in some other TU, then this works for me.

[timurrrr]

Out of date?

lib/CodeGen/CGCXXABI.h

public:
   ///   function
   /// \param CookieSize - an out parameter which will be initialized
   ///   with the size of the cookie, or zero if there is no cookie
   virtual void ReadArrayCookie(CodeGenFunction &CGF, llvm::Value *Ptr,
                                const CXXDeleteExpr *expr,
                                QualType ElementType, llvm::Value *&NumElements,
                                llvm::Value *&AllocPtr, CharUnits &CookieSize);
 
+  /// Returns true if the ABI requires that we emit a definition for this
+  /// function, given that we don't have a definition for it in the TU.
+  virtual bool NeedsBodylessEmission(GlobalDecl GD);
+
 protected:
   /// Returns the extra size required in order to store the array
   /// cookie for the given type.  Assumes that an array cookie is
   /// required.
   virtual CharUnits getArrayCookieSizeImpl(QualType elementType);
 
   /// Reads the array cookie for an allocation which is known to have one.
   /// This is called by the standard implementation of ReadArrayCookie.

lib/CodeGen/CGCXXABI.cpp

void CGCXXABI::EmitThreadLocalInitFuncs(
     llvm::Function *InitFunc) {
 }
 
 LValue CGCXXABI::EmitThreadLocalDeclRefExpr(CodeGenFunction &CGF,
                                           const DeclRefExpr *DRE) {
   ErrorUnsupportedABI(CGF, "odr-use of thread_local global");
   return LValue();
 }
+
+bool CGCXXABI::NeedsBodylessEmission(GlobalDecl GD) {
+  return false;
+}

lib/CodeGen/CodeGenModule.cpp

// in a vtable, unless it's already marked as used.
     const FunctionDecl *FD = cast<FunctionDecl>(D.getDecl());
     FD = FD->getMostRecentDecl();
     do {
       if (isa<CXXRecordDecl>(FD->getLexicalDeclContext())) {
         if (FD->isImplicit() && !ForVTable) {
           assert(FD->isUsed() && "Sema didn't mark implicit function as used!");
           DeferredDeclsToEmit.push_back(D.getWithDecl(FD));
           break;
-        } else if (FD->doesThisDeclarationHaveABody()) {
+        } else if (FD->doesThisDeclarationHaveABody() ||
+                   getCXXABI().NeedsBodylessEmission(D)) {
           DeferredDeclsToEmit.push_back(D.getWithDecl(FD));
           break;
         }
       }
       FD = FD->getPreviousDecl();
     } while (FD);
   }