[clang][Interp] Don't call getSource() on functions without a body

For builtin functions, we create a Function instance without a body or
code. When emitting diagnostics from them, we need a proper SourceInfo
to point to, but the only thing we can use is the call site of the
builtin function.

Differential Revision: https://reviews.llvm.org/D149824

Author: tbaederr

clang/lib/AST/Interp/EvalEmitter.h

@@ -71,7 +71,7 @@ class EvalEmitter : public SourceMapper {
 
   /// Returns the source location of the current opcode.
   SourceInfo getSource(const Function *F, CodePtr PC) const override {
-    return F ? F->getSource(PC) : CurrentSource;
+    return (F && F->hasBody()) ? F->getSource(PC) : CurrentSource;
   }
 
   /// Parameter indices.

clang/lib/AST/Interp/Function.cpp

@@ -32,6 +32,7 @@ Function::ParamDescriptor Function::getParamDescriptor(unsigned Offset) const {
 SourceInfo Function::getSource(CodePtr PC) const {
   assert(PC >= getCodeBegin() && "PC does not belong to this function");
   assert(PC <= getCodeEnd() && "PC Does not belong to this function");
+  assert(hasBody() && "Function has no body");
   unsigned Offset = PC - getCodeBegin();
   using Elem = std::pair<unsigned, SourceInfo>;
   auto It = llvm::lower_bound(SrcMap, Elem{Offset, {}}, llvm::less_first());