Add the notion of deferred diagnostics.

[jlebar]

Summary

This patch lets you create diagnostics that are emitted if and only if a
particular FunctionDecl is codegen'ed.

This is necessary for CUDA, where some constructs -- e.g. calls from
host+device functions to host functions when compiling for device -- are
allowed to appear in semantically-correct programs, but only if they're
never codegen'ed.

[tra]

clang/lib/CodeGen/CodeGenModule.cpp

2886

eit->emit.
"don't do X, but don't do Y" construction sounds awkward to me.
I'd reword the whole comment in terms of what the code does -- if there are diagnostics, only collect them to emit at the end of codegen. Otherwise, proceed to emit function definition.

[jlebar]

Address review comments, and don't abort codegen'ing a function if it has only
deferred warnings -- check specifically for errors.

[jlebar]

Reid, I'd still like you to have a look at this one if you don't mind, since it's outside my and Art's core competencies.

clang/lib/CodeGen/CodeGenModule.cpp

2886

Thanks. I tried to reword it, phal.

I also realized that this was skipping functions if they contained *any* deferred diags, but that's not right -- we only want to skip functions that contain deferred errors. Fixed that too.

I wish I could use StoredDiagnostic instead of PartialDiagnosticAt, but I don't see a way to create a StoredDiagnostic for an error without setting the HasError bit in the DiagnosticEngine. I need to carefully avoid setting that bit, otherwise we don't even make it to codegen. (In fact it looks like the code for emitting diagnostics assumes that creating a StoredDiagnostic sets the bit, because I don't see it setting that bit when we emit the StoredDiagnostic.)

[rnk]

Sorry for the delay, was trying to stay focused on debugging

clang/include/clang/AST/Decl.h

1647

Decl memory is pretty precious, I think you'll be better off with a map from Decl* to TinyPtrVector in the ASTContext. Just pass the ASTContext into takeDeferredDiags.

[jlebar]

Move deferred diags storage into ASTContext.

[rnk]

lgtm

clang/include/clang/AST/Decl.h

llvm::PointerUnion4<FunctionTemplateDecl *,
                       FunctionTemplateSpecializationInfo *,
                       DependentFunctionTemplateSpecializationInfo *>
     TemplateOrSpecialization;
 
   /// DNLoc - Provides source/type location info for the
   /// declaration name embedded in the DeclaratorDecl base class.
   DeclarationNameLoc DNLoc;
 
+  /// Storage for diagnostics deferred until this function is codegen'ed (if it
+  /// ever is).
+  ///
+  /// These are rarely used, so we use a pointer-to-vector to save two words
+  /// inside FunctionDecl.  This is mutable because emitting diagnostics (which
+  /// clears this list) needs to be a logically-const operation.
+  mutable std::unique_ptr<std::vector<PartialDiagnosticAt>> DeferredDiags;
+
   /// \brief Specify that this function declaration is actually a function
   /// template specialization.
   ///
   /// \param C the ASTContext.
   ///
   /// \param Template the function template that this function template
   /// specialization specializes.
   ///
public:
   bool isOutOfLine() const override;
 
   /// \brief Identify a memory copying or setting function.
   /// If the given function is a memory copy or setting function, returns
   /// the corresponding Builtin ID. If the function is not a memory function,
   /// returns 0.
   unsigned getMemoryFunctionKind() const;
 
+  /// Add a diagnostic to be emitted if and when this function is codegen'ed.
+  void addDeferredDiag(PartialDiagnosticAt PD);
+
+  /// Gets this object's list of deferred diagnostics, if there are any.
+  ///
+  /// Although this is logically const, it clears our list of deferred diags.
+  std::vector<PartialDiagnosticAt> takeDeferredDiags() const;
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) {
     return K >= firstFunction && K <= lastFunction;
   }
   static DeclContext *castToDeclContext(const FunctionDecl *D) {
     return static_cast<DeclContext *>(const_cast<FunctionDecl*>(D));
   }

clang/lib/AST/Decl.cpp

if (isExternC()) {
       else if (FnInfo->isStr("strlen"))
         return Builtin::BIstrlen;
     }
     break;
   }
   return 0;
 }
 
+void FunctionDecl::addDeferredDiag(PartialDiagnosticAt PD) {
+  if (!DeferredDiags)
+    DeferredDiags = llvm::make_unique<std::vector<PartialDiagnosticAt>>();
+  DeferredDiags->emplace_back(PD);
+}
+
+std::vector<PartialDiagnosticAt> FunctionDecl::takeDeferredDiags() const {
+  if (!DeferredDiags)
+    return {};
+  assert(!DeferredDiags->empty() &&
+         "DeferredDiags should be non-null only if it's also non-empty.");
+  auto Ret = std::move(*DeferredDiags);
+  DeferredDiags.reset();
+  return Ret;
+}
+
 //===----------------------------------------------------------------------===//
 // FieldDecl Implementation
 //===----------------------------------------------------------------------===//
 
 FieldDecl *FieldDecl::Create(const ASTContext &C, DeclContext *DC,
                              SourceLocation StartLoc, SourceLocation IdLoc,
                              IdentifierInfo *Id, QualType T,
                              TypeSourceInfo *TInfo, Expr *BW, bool Mutable,

clang/lib/CodeGen/CodeGenModule.h

private:
 
   std::unique_ptr<CoverageMappingModuleGen> CoverageMapping;
 
   /// Mapping from canonical types to their metadata identifiers. We need to
   /// maintain this mapping because identifiers may be formed from distinct
   /// MDNodes.
   llvm::DenseMap<QualType, llvm::Metadata *> MetadataIdMap;
 
+  /// Diags gathered from FunctionDecl::takeDeferredDiags().  Emitted at the
+  /// very end of codegen.
+  std::vector<std::pair<SourceLocation, PartialDiagnostic>> DeferredDiags;
+
 public:
   CodeGenModule(ASTContext &C, const HeaderSearchOptions &headersearchopts,
                 const PreprocessorOptions &ppopts,
                 const CodeGenOptions &CodeGenOpts, llvm::Module &M,
                 DiagnosticsEngine &Diags,
                 CoverageSourceInfo *CoverageInfo = nullptr);
 
   ~CodeGenModule();

clang/lib/CodeGen/CodeGenModule.cpp

if (getCodeGenOpts().EmitGcovArcs || getCodeGenOpts().EmitGcovNotes)
     EmitCoverageFile();
 
   if (DebugInfo)
     DebugInfo->finalize();
 
   EmitVersionIdentMetadata();
 
   EmitTargetMetadata();
+
+  // Emit any deferred diagnostics gathered during codegen.  We didn't emit them
+  // when we first discovered them because that would have halted codegen,
+  // preventing us from gathering other deferred diags.
+  for (const PartialDiagnosticAt &DiagAt : DeferredDiags) {
+    SourceLocation Loc = DiagAt.first;
+    const PartialDiagnostic &PD = DiagAt.second;
+    DiagnosticBuilder Builder(getDiags().Report(Loc, PD.getDiagID()));
+    PD.Emit(Builder);
+  }
 }
 
 void CodeGenModule::UpdateCompletedType(const TagDecl *TD) {
   // Make sure that this type is translated.
   Types.UpdateCompletedType(TD);
 }
 
 void CodeGenModule::RefreshTypeCacheForClass(const CXXRecordDecl *RD) {
void CodeGenModule::HandleCXXStaticMemberVarInstantiation(VarDecl *VD) {
 
   EmitTopLevelDecl(VD);
 }
 
 void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD,
                                                  llvm::GlobalValue *GV) {
   const auto *D = cast<FunctionDecl>(GD.getDecl());
 
+  // Emit this function's deferred diagnostics, if none of them are errors.  If
+  // any of them are errors, don't codegen the function, but also don't emit any
+  // of the diagnostics just yet.  Emitting an error during codegen stops
+  // further codegen, and we want to display as many deferred diags as possible.
+  // We'll emit the now twice-deferred diags at the very end of codegen.
+  //
+  // (If a function has both error and non-error diags, we don't emit the
+  // non-error diags here, because order can be significant, e.g. with notes
+  // that follow errors.)
+  auto Diags = D->takeDeferredDiags();
+  bool HasError = llvm::any_of(Diags, [this](const PartialDiagnosticAt &PDAt) {
+    return getDiags().getDiagnosticLevel(PDAt.second.getDiagID(), PDAt.first) >=
+           DiagnosticsEngine::Error;
+  });
+  if (HasError) {
+    DeferredDiags.insert(DeferredDiags.end(),
+                         std::make_move_iterator(Diags.begin()),
+                         std::make_move_iterator(Diags.end()));
+    return;
+  }
+  for (PartialDiagnosticAt &PDAt : Diags) {
+    const SourceLocation &Loc = PDAt.first;
+    const PartialDiagnostic &PD = PDAt.second;
+    DiagnosticBuilder Builder(getDiags().Report(Loc, PD.getDiagID()));
+    PD.Emit(Builder);
+  }
+
   // Compute the function info and LLVM type.
   const CGFunctionInfo &FI = getTypes().arrangeGlobalDeclaration(GD);
   llvm::FunctionType *Ty = getTypes().GetFunctionType(FI);
 
   // Get or create the prototype for the function.
   if (!GV || (GV->getType()->getElementType() != Ty))
     GV = cast<llvm::GlobalValue>(GetAddrOfFunction(GD, Ty, /*ForVTable=*/false,
                                                    /*DontDefer=*/true,