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

This happens only in error cases, but we need to handle it anyway.

Differential Revision: https://reviews.llvm.org/D136831

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

@@ -98,7 +98,8 @@ bool ByteCodeStmtGen<Emitter>::visitFunc(const FunctionDecl *F) {
   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();

clang/lib/AST/Interp/Program.cpp

@@ -221,6 +221,11 @@ Record *Program::getOrCreateRecord(const RecordDecl *RD) {
     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.
@@ -294,7 +299,7 @@ Record *Program::getOrCreateRecord(const RecordDecl *RD) {
 
   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;
 }
 

clang/lib/AST/Interp/Program.h

@@ -51,8 +51,10 @@ public:
     // 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();
+    }
   }
 
   /// Marshals a native pointer to an ID for embedding in bytecode.

clang/test/AST/Interp/records.cpp

@@ -133,6 +133,20 @@ constexpr C RVOAndParams(const C *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 Bar *pb = nullptr;
+
 constexpr int locals() {
   C c;
   c.a = 10;