[clang][Interp] Protect Record creation against infinite recusion

[tbaeder]

Summary

This only happens in error cases as far as I know, e.g. the attached test case.

[aaron.ballman]

LGTM!

[shafik]

LGTM

clang/test/AST/Interp/records.cpp

144

How about static constexpr B* bp=nullptr;

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

 bool ByteCodeStmtGen<Emitter>::visitFunc(const FunctionDecl *F) {
   // Classify the return type.
   ReturnType = this->classify(F->getReturnType());
 
   // Constructor. Set up field initializers.
   if (const auto Ctor = dyn_cast<CXXConstructorDecl>(F)) {
     const RecordDecl *RD = Ctor->getParent();
     const Record *R = this->getRecord(RD);
-    assert(R);
+    if (!R)
+      return false;
 
     for (const auto *Init : Ctor->inits()) {
       const Expr *InitExpr = Init->getInit();
       if (const FieldDecl *Member = Init->getMember()) {
         const Record::Field *F = R->getField(Member);
 
         if (Optional<PrimType> T = this->classify(InitExpr)) {
           if (!this->emitThis(InitExpr))

clang/lib/AST/Interp/Program.h

 class Program final {
 public:
   Program(Context &Ctx) : Ctx(Ctx) {}
 
   ~Program() {
     // Records might actually allocate memory themselves, but they
     // are allocated using a BumpPtrAllocator. Call their desctructors
     // here manually so they are properly freeing their resources.
-    for (auto RecordPair : Records)
-      RecordPair.second->~Record();
+    for (auto RecordPair : Records) {
+      if (Record *R = RecordPair.second)
+        R->~Record();
+    }
 
     // Manually destroy all the blocks. They are almost all harmless,
     // but primitive arrays might have an InitMap* heap allocated and
     // that needs to be freed.
     for (Global *G : Globals) {
       G->block()->invokeDtor();
     }
   }

clang/lib/AST/Interp/Program.cpp

if (!RD)
     return nullptr;
 
   // Deduplicate records.
   auto It = Records.find(RD);
   if (It != Records.end()) {
     return It->second;
   }
 
+  // We insert nullptr now and replace that later, so recursive calls
+  // to this function with the same RecordDecl don't run into
+  // infinite recursion.
+  Records.insert({RD, nullptr});
+
   // Number of bytes required by fields and base classes.
   unsigned BaseSize = 0;
   // Number of bytes required by virtual base.
   unsigned VirtSize = 0;
 
   // Helper to get a base descriptor.
   auto GetBaseDesc = [this](const RecordDecl *BD, Record *BR) -> Descriptor * {
     if (!BR)
for (const FieldDecl *FD : RD->fields()) {
     if (!Desc)
       return nullptr;
     Fields.push_back({FD, BaseSize, Desc});
     BaseSize += align(Desc->getAllocSize());
   }
 
   Record *R = new (Allocator) Record(RD, std::move(Bases), std::move(Fields),
                                      std::move(VirtBases), VirtSize, BaseSize);
-  Records.insert({RD, R});
+  Records[RD] = R;
   return R;
 }
 
 Descriptor *Program::createDescriptor(const DeclTy &D, const Type *Ty,
                                       Descriptor::MetadataSize MDSize,
                                       bool IsConst, bool IsTemporary,
                                       bool IsMutable, const Expr *Init) {
   // Classes and structures.

clang/test/AST/Interp/records.cpp

 // FIXME: In c++14, this uses a MaterializeTemporaryExpr,
 //   which the new interpreter doesn't support yet.
 constexpr C RVOAndParams(const C *c) {
   return C();
 }
 constexpr C RVOAndParamsResult = RVOAndParams(&c);
 #endif
 
+class Bar { // expected-note {{definition of 'Bar' is not complete}} \
+            // ref-note {{definition of 'Bar' is not complete}}
+public:
+  constexpr Bar(){}
+  constexpr Bar b; // expected-error {{cannot be constexpr}} \
+                   // expected-error {{has incomplete type 'const Bar'}} \
+                   // ref-error {{cannot be constexpr}} \
+                   // ref-error {{has incomplete type 'const Bar'}}
+};
+constexpr Bar B; // expected-error {{must be initialized by a constant expression}} \
+                 // expected-error {{failed to evaluate an expression}} \
+                 // ref-error {{must be initialized by a constant expression}}
+
 constexpr int locals() {
   C c;
   c.a = 10;
 
   // Assignment, not an initializer.
   // c = C(); FIXME
   c.a = 10;