Re: [patch, fortran] Optionally improve debugging of auxiliary variables

[Iain Sandoe via Gcc-patches]

Thomas Koenig via Fortran <fort...@gcc.gnu.org> wrote:

Hello world,

I have struggled with debugging the GENERIC generated by the
Fortran front end because it is only possible to look at the
code via -fdump-tree-original, but it is not possible to
inspect the values; additionally, the D.3456 form makes it
hard to read which variable is which.

This patch adds a flag which gives all variables generated by
Fortran a name and makes them visible to debuggers. As an
example, compiler-generated variables now look like this
(for a "Hello, world" program):

 {
   struct __st_parameter_dt dt_parm:0;

   dt_parm:0.common.filename = &"hello.f90"[1]{lb: 1 sz: 1};
   dt_parm:0.common.line = 2;
   dt_parm:0.common.flags = 128;
   dt_parm:0.common.unit = 6;
   _gfortran_st_write (&dt_parm:0);
   _gfortran_transfer_character_write (&dt_parm:0, &"Hello, world"[1]{lb: 1 sz: 
1}, 12);
   _gfortran_st_write_done (&dt_parm:0);
 }

Note the colon in the variable name, which I chose because it is
not in the user's namespace, and gdb does not choke on it.

If it’s part of a symbol used by the rest of the toolchain (assembler, linker
debugger) then it’s also important to note that some OS/tool pairs might
be more constrained than the one you’ve tested.  In particular, some
assemblers will not accept all characters in an  identifier.

In order to inspect the variables, you usually have to step
a bit through the generated assembly code, but you can then
print the values, manipulate them etc (and sometimes also hit
an internal error in gdb).

--- a/gcc/fortran/trans.c
+++ b/gcc/fortran/trans.c
@@ -73,6 +73,40 @@ gfc_advance_chain (tree t, int n)
   return t;

+  /* We want debug info for it.  */
+  DECL_IGNORED_P (t) = 0;
+  /* It should not be nameless.  */
+  DECL_NAMELESS (t) = 0;

 tree
@@ -80,6 +114,9 @@ gfc_create_var_np (tree type, const char *prefix)
 {
   tree t;

+  if (flag_debug_aux_vars)
+    return create_var_debug_raw (type, prefix);
+
   t = create_tmp_var_raw (type, prefix);

You could take advantage of the understanding of assembler identifier rules
built into create_var_debug_raw()

.. perhaps (totally untested)….

if (flag_debug_aux_vars)
  prefix = prefix ? prefix :  “gfc”;

t = create_tmp_var_raw (type, prefix);
if (flag_debug_aux_vars)
  {
     /* We want debug info for it.  */
    DECL_IGNORED_P (t) = false;
    /* It should not be nameless.  */
    DECL_NAMELESS (t) = false;
  }

 return t;


… or doens’t this approach work for some reason?
cheers
Iain