On 07/03/2017 11:53 AM, Richard Biener wrote:
On Mon, 3 Jul 2017, Tom de Vries wrote:
On 07/03/2017 09:05 AM, Richard Biener wrote:
On Mon, 3 Jul 2017, Tom de Vries wrote:
Hi,
this patch adds a debug function dotfn and a convenience macro DOTFN
similar
to dot-fn in gdbhooks.py.
It can be used to have the compiler:
- dump a control flow graph, or
- pop up a control flow graph window
at specific moments in the compilation flow, for debugging purposes.
Bootstrapped and reg-tested on x86_64.
Used for debugging PR81192.
OK for trunk?
Why's dot-fn not enough? > I'd rather extend stuff in gdbhooks.py than
adding this kind of stuff to gcc itself.
When expressing where and when to dump or pop-up a control flow graph,
sometimes it's easier for me to do that in C than in gdb scripting.
Ah, you mean by patching GCC. Yeah, I can see that this is useful
in some cases. OTOH I had dot-fn this way in my local dev tree for
a few years ...
I'm retracting my objection but leave approval to somebody else
just to see if we can arrive at any consensus for "advanced"
debug stuff in GCC itself.
Ack.
For my usecase the gdb python stuff is now nearly perfect -- apart
from the cases where graph generation ICEs (like corrupt loop info).
I suppose we can make a dotfn variant that calls draw_cfg_nodes_no_loops
even if loop info is present.
Btw, I think this needs fixing:
...
/* Draw all edges in the CFG. Retreating edges are drawin as not
constraining, this makes the layout of the graph better.
(??? Calling mark_dfs_back may change the compiler's behavior when
dumping, but computing back edges here for ourselves is also not
desirable.) */
static void
draw_cfg_edges (pretty_printer *pp, struct function *fun)
{
basic_block bb;
mark_dfs_back_edges ();
FOR_ALL_BB_FN (bb, cfun)
draw_cfg_node_succ_edges (pp, fun->funcdef_no, bb);
...
We don't want that calling a debug function changes compiler behavior
(something I ran into while debugging PR81192).
Any suggestion on how to address this? We could allocate a bitmap before
and save the edge flag for all edges, and restore afterwards.
Thanks,
- Tom
