Re: Debugging the tree object constructed by cp_parser

[David Malcolm <dmalcolm@redhat.com>]

On Mon, 2023-12-04 at 10:09 -0500, Stan Srednyak wrote:
> Hi David, thanks for your email. I really appreciate it.
> 
> Your notes are certainly of help, but I also had a specific question:
> how
> to access the trees as they are being constructed by the front end.
> Do you
> have an answer to this?

You could try putting a breakpoint on "make_node", and then
conditionalizing it so it only fires when code ==
TRANSLATION_UNIT_DECL:

(gdb) break make_node
Breakpoint 5 at 0x1675250: file ../../src/gcc/tree.cc, line 1188.

(gdb) cond 5 code==TRANSLATION_UNIT_DECL

(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n) y

[...snip...]

Breakpoint 5, make_node (code=TRANSLATION_UNIT_DECL) at
../../src/gcc/tree.cc:1188
1188	{

(gdb) bt
#0  make_node (code=TRANSLATION_UNIT_DECL) at
../../src/gcc/tree.cc:1188
#1  0x0000000001675aae in build_decl (loc=0,
code=TRANSLATION_UNIT_DECL, name=<identifier_node 0x7fffea664b00
/tmp/t.c>, type=<tree 0x0>)
    at ../../src/gcc/tree.cc:5379
#2  0x000000000169644c in build_translation_unit_decl (name=<optimized
out>) at ../../src/gcc/tree.cc:5432
#3  0x0000000000b1e181 in cxx_init_decl_processing () at
../../src/gcc/tree.h:3749
#4  0x0000000000b6b904 in cxx_init () at ../../src/gcc/cp/lex.cc:336
#5  0x0000000000a4e23a in lang_dependent_init (name=0x34bd820
"/tmp/t.c") at ../../src/gcc/toplev.cc:1838
#6  do_compile () at ../../src/gcc/toplev.cc:2136
#7  toplev::main (this=this@entry=0x7fffffffdd6e, argc=<optimized out>,
argc@entry=22, argv=<optimized out>, argv@entry=0x7fffffffde78)
    at ../../src/gcc/toplev.cc:2307
#8  0x0000000000a502f5 in main (argc=22, argv=0x7fffffffde78) at
../../src/gcc/main.cc:39


Dave

> 
> I looked into GCC internals docs. The section on the front  end (sec
> 5) is
> wonderfully concise, of course, but it does not answer this question.
> Do
> you know any sources where this is documented?
> 
> best regards,
> Stan
> 
> On Sun, Dec 3, 2023 at 1:00 PM David Malcolm <dmalcolm@redhat.com>
> wrote:
> 
> > On Sat, 2023-12-02 at 17:41 -0500, Stan Srednyak via Gcc wrote:
> > > Dear GCC community,
> > > 
> > > I am assigned the task to debug the trees as being produced by
> > > the
> > > cp_parser. I was able to print some of the trees using the
> > > debug_tree()
> > > function. But I am still confused as to where is the tree object
> > > that
> > > corresponds to the translation unit being parsed. There is no
> > > such
> > > field in
> > > cp_parser, and in the few tiers of functions calls starting from
> > > parse_file() function that I followed so far, I was not able to
> > > find
> > > any
> > > variable remotely similar to the AST of functions/structs etc.
> > > that
> > > must be
> > > constructed by this great piece of software. I would very much
> > > appreciate
> > > any explanation from the great experts in gcc on this mailing
> > > list. I
> > > posted a thread at gcc-help, but apparently it is too obvious of
> > > a
> > > question
> > > to be addressed there.
> > 
> > Hi Stan
> > 
> > FWIW I've written some notes on debugging GCC:
> > https://gcc-newbies-guide.readthedocs.io/en/latest/debugging.html
> > 
> > and in particular you might find the following useful:
> > 
> > https://gcc-newbies-guide.readthedocs.io/en/latest/debugging.html#how-do-i-find-where-a-particular-tree-was-created
> > 
> > Hope this is helpful
> > Dave
> > 
> >