[CGDebugInfo] return early on failed dyn_cast

[nickdesaulniers]

Summary

This was flagged in https://www.viva64.com/en/b/0629/ under "Snippet No.
39".

I looked at making CGDebugInfo::getFunctionFwdDeclOrStub take a
FunctionDecl as its first argument, but this quickly became untenable.

[nickdesaulniers]

Also of note is that no existing test covers this case.

[dblaikie]

Looks like this may've already been addressed in cfee2efc57b27ce7eed932528e219a99f934d3ca ?

[nickdesaulniers]

Heh, @RKSimon and I were going through fixing up warnings noted in that blog.

clang/lib/CodeGen/CGDebugInfo.cpp

if (DC->isRecord())
     DC = CGM.getContext().getTranslationUnitDecl();
 
   llvm::DIScope *Mod = getParentModuleOrNull(VD);
   VDContext = getContextDescriptor(cast<Decl>(DC), Mod ? Mod : TheCU);
 }
 
 llvm::DISubprogram *CGDebugInfo::getFunctionFwdDeclOrStub(GlobalDecl GD,
                                                           bool Stub) {
+  auto *FD = dyn_cast<FunctionDecl>(GD.getDecl());
+  if (!FD)
+    return nullptr;
+
   llvm::DINodeArray TParamsArray;
   StringRef Name, LinkageName;
   llvm::DINode::DIFlags Flags = llvm::DINode::FlagZero;
   llvm::DISubprogram::DISPFlags SPFlags = llvm::DISubprogram::SPFlagZero;
   SourceLocation Loc = GD.getDecl()->getLocation();
   llvm::DIFile *Unit = getOrCreateFile(Loc);
   llvm::DIScope *DContext = Unit;
   unsigned Line = getLineNumber(Loc);
   collectFunctionDeclProps(GD, Unit, Name, LinkageName, DContext, TParamsArray,
                            Flags);
-  auto *FD = dyn_cast<FunctionDecl>(GD.getDecl());
-
   // Build function type.
   SmallVector<QualType, 16> ArgTypes;
-  if (FD)
-    for (const ParmVarDecl *Parm : FD->parameters())
-      ArgTypes.push_back(Parm->getType());
   CallingConv CC = FD->getType()->castAs<FunctionType>()->getCallConv();
   QualType FnType = CGM.getContext().getFunctionType(
       FD->getReturnType(), ArgTypes, FunctionProtoType::ExtProtoInfo(CC));
   if (!FD->isExternallyVisible())
     SPFlags |= llvm::DISubprogram::SPFlagLocalToUnit;
   if (CGM.getLangOpts().Optimize)
     SPFlags |= llvm::DISubprogram::SPFlagOptimized;