[clang][Interp] Properly identify not-yet-defined functions

Since we now handle functions without a body as well, we can't just use
getHasBody() anymore. Funtions that haven't been defined yet are those
that don't have a body *and* aren't valid.

Also, just pass the information about whether the Function has a body or
not along from the FunctionDecl.

Differential Revision: https://reviews.llvm.org/D141591

clang/lib/AST/Interp/ByteCodeEmitter.cpp

@@ -92,7 +92,7 @@ ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl) {
 
     // Set the function's code.
     Func->setCode(NextLocalOffset, std::move(Code), std::move(SrcMap),
-                  std::move(Scopes));
+                  std::move(Scopes), FuncDecl->hasBody());
     Func->setIsFullyCompiled(true);
     return Func;
   }

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1465,7 +1465,7 @@ const Function *ByteCodeExprGen<Emitter>::getFunction(const FunctionDecl *FD) {
   assert(FD);
   const Function *Func = P.getFunction(FD);
   bool IsBeingCompiled = Func && !Func->isFullyCompiled();
-  bool WasNotDefined = Func && !Func->hasBody();
+  bool WasNotDefined = Func && !Func->isConstexpr() && !Func->hasBody();
 
   if (IsBeingCompiled)
     return Func;

clang/lib/AST/Interp/Function.h

@@ -157,14 +157,15 @@ class Function final {
            bool HasThisPointer, bool HasRVO);
 
   /// Sets the code of a function.
-  void setCode(unsigned NewFrameSize, std::vector<char> &&NewCode, SourceMap &&NewSrcMap,
-               llvm::SmallVector<Scope, 2> &&NewScopes) {
+  void setCode(unsigned NewFrameSize, std::vector<char> &&NewCode,
+               SourceMap &&NewSrcMap, llvm::SmallVector<Scope, 2> &&NewScopes,
+               bool NewHasBody) {
     FrameSize = NewFrameSize;
     Code = std::move(NewCode);
     SrcMap = std::move(NewSrcMap);
     Scopes = std::move(NewScopes);
     IsValid = true;
-    HasBody = true;
+    HasBody = NewHasBody;
   }
 
   void setIsFullyCompiled(bool FC) { IsFullyCompiled = FC; }

clang/test/AST/Interp/functions.cpp

@@ -162,3 +162,21 @@ namespace FunctionReturnType {
 }
 
 }
+
+struct F {
+  constexpr bool ok() const {
+    return okRecurse();
+  }
+  constexpr bool okRecurse() const {
+    return true;
+  }
+};
+
+struct BodylessMemberFunction {
+  constexpr int first() const {
+    return second();
+  }
+  constexpr int second() const {
+    return 1;
+  }
+};