default values: store as staticvarsyms in staticsymtable

Previously, they were stored as localvarsyms in either the localsymtable
(for procedures/functions) or as localvarsyms in the staticsymtable (for
init/fini code of units/main programs). The latter was a hack (staticsymtables
normally cannot contain localvarsyms) and caused the temp allocator to also
allocate them as a local in fini code even if the default was only in the init
code.

The new approach ensures at most one copy gets allocated per unit, it doesn't
require explicit initialisation (since staticvarsyms are in bss -> zeroed by
default), gets rid of the localvarsyms in staticsymtables, and as a bonus
solves an issue with inconsistent LLVM debug information for the localvarsym
in init/fini code (since the staticsymtable is shared between the init and
fini code, so was the local, and therefore we generated debug info stating
it was defined in the fini code but within the scope of the init code).

Resolves #40395

compiler/ninl.pas

@@ -138,7 +138,7 @@ implementation
       symconst,symdef,symsym,symcpu,symtable,paramgr,defcmp,defutil,symbase,
       cpuinfo,cpubase,
       pass_1,
-      ncal,ncon,ncnv,nadd,nld,nbas,nflw,nmem,nmat,nutils,
+      ncal,ncon,ncnv,nadd,nld,nbas,nflw,nmem,nmat,nutils,ngenutil,
       nobjc,objcdef,
       cgbase,procinfo;
 
@@ -445,6 +445,13 @@ implementation
               not (def.typ in [arraydef,recorddef,variantdef,objectdef,procvardef]) or
               ((def.typ=objectdef) and not is_object(def)) then
             internalerror(201202101);
+
+          if df_generic in current_procinfo.procdef.defoptions then
+            begin
+              result:=cpointerconstnode.create(0,def);
+              exit;
+            end;
+
           { extra '$' prefix because on darwin the result of makemangledname
             is prefixed by '_' and hence adding a '$' at the start of the
             prefix passed to makemangledname doesn't help (the whole point of
@@ -462,20 +469,20 @@ implementation
           if assigned(current_procinfo) then
             begin
               { the default sym is always part of the current procedure/function }
-              srsymtable:=current_procinfo.procdef.localst;
+              srsymtable:=current_module.localsymtable;
               srsym:=tsym(srsymtable.findwithhash(hashedid));
               if not assigned(srsym) then
                 begin
                   { no valid default variable found, so create it }
-                  srsym:=clocalvarsym.create(defaultname,vs_const,def,[]);
+                  srsym:=cstaticvarsym.create(defaultname,vs_const,def,[]);
                   srsymtable.insertsym(srsym);
+                  cnodeutils.insertbssdata(tstaticvarsym(srsym));
+
                   { mark the staticvarsym as typedconst }
                   include(tabstractvarsym(srsym).varoptions,vo_is_typed_const);
                   include(tabstractvarsym(srsym).varoptions,vo_is_default_var);
                   { The variable has a value assigned }
                   tabstractvarsym(srsym).varstate:=vs_initialised;
-                  { the variable can't be placed in a register }
-                  tabstractvarsym(srsym).varregable:=vr_none;
                 end;
               result:=cloadnode.create(srsym,srsymtable);
             end

compiler/psub.pas

@@ -275,34 +275,6 @@ implementation
                       PROCEDURE/FUNCTION BODY PARSING
 ****************************************************************************}
 
-    procedure initializedefaultvars(p:TObject;arg:pointer);
-      var
-        b : tblocknode;
-      begin
-        if tsym(p).typ<>localvarsym then
-         exit;
-        with tabstractnormalvarsym(p) do
-         begin
-           if (vo_is_default_var in varoptions) and (vardef.size>0) then
-             begin
-               b:=tblocknode(arg);
-               b.left:=cstatementnode.create(
-                         ccallnode.createintern('fpc_zeromem',
-                           ccallparanode.create(
-                             cordconstnode.create(vardef.size,sizeuinttype,false),
-                             ccallparanode.create(
-                               caddrnode.create_internal(
-                                 cloadnode.create(tsym(p),tsym(p).owner)),
-                                 nil
-                               )
-                             )
-                           ),
-                         b.left);
-             end;
-         end;
-      end;
-
-
     procedure initializevars(p:TObject;arg:pointer);
       var
         b : tblocknode;
@@ -320,8 +292,6 @@ implementation
                             cloadnode.create(defaultconstsym,defaultconstsym.owner)),
                         b.left);
             end
-           else
-             initializedefaultvars(p,arg);
          end;
       end;
 
@@ -365,15 +335,6 @@ implementation
            current_filepos:=current_procinfo.entrypos;
            current_procinfo.procdef.localst.SymList.ForEachCall(@initializevars,block);
            current_filepos:=oldfilepos;
-         end
-        else if current_procinfo.procdef.localst.symtabletype=staticsymtable then
-         begin
-           { for program and unit initialization code we also need to
-             initialize the local variables used of Default() }
-           oldfilepos:=current_filepos;
-           current_filepos:=current_procinfo.entrypos;
-           current_procinfo.procdef.localst.SymList.ForEachCall(@initializedefaultvars,block);
-           current_filepos:=oldfilepos;
          end;
 
         if assigned(current_procinfo.procdef.parentfpstruct) then

tests/webtbs/tw40395.pp

@@ -0,0 +1,20 @@
+{ %norun }
+
+{$mode objfpc}
+
+unit tw40395;
+
+interface
+
+implementation
+
+var x: TRTLCriticalSection;
+
+initialization
+x := default(TRTLCriticalSection);
+InitCriticalSection(x);
+
+finalization
+DoneCriticalsection(x);
+
+end.

tests/webtbs/tw40395a.pp

@@ -0,0 +1,18 @@
+{ %norun }
+
+{$mode objfpc}
+
+unit tw40395a;
+
+interface
+
+implementation
+
+var x: TRTLCriticalSection;
+
+finalization
+x := default(TRTLCriticalSection);
+InitCriticalSection(x);
+DoneCriticalsection(x);
+
+end.