[clang][bytecode][NFC] Only call getSource() when necessary (#125419)

Author: tbaederr

clang/lib/AST/ByteCode/Interp.cpp

@@ -65,17 +65,17 @@ static void diagnoseNonConstVariable(InterpState &S, CodePtr OpPC,
                                      const ValueDecl *VD);
 static bool diagnoseUnknownDecl(InterpState &S, CodePtr OpPC,
                                 const ValueDecl *D) {
-  const SourceInfo &E = S.Current->getSource(OpPC);
 
   if (isa<ParmVarDecl>(D)) {
     if (D->getType()->isReferenceType())
       return false;
 
+    const SourceInfo &Loc = S.Current->getSource(OpPC);
     if (S.getLangOpts().CPlusPlus11) {
-      S.FFDiag(E, diag::note_constexpr_function_param_value_unknown) << D;
+      S.FFDiag(Loc, diag::note_constexpr_function_param_value_unknown) << D;
       S.Note(D->getLocation(), diag::note_declared_at) << D->getSourceRange();
     } else {
-      S.FFDiag(E);
+      S.FFDiag(Loc);
     }
     return false;
   }