On Tue, 2011-07-12 at 09:43 +0100, Paulo J. Matos wrote:
> On 12/07/11 08:22, Paolo Bonzini wrote:
> > On 07/11/2011 07:56 PM, David Malcolm wrote:
> >> Hope this is fun/helpful (and that I'm correctly interpreting the data!)
> >
> > You are, and it shows some bugs even. gimple_lcx is obviously destroyed
> > by expand, and I find it unlikely that no pass ever introduces a
> > critical edge...
> >
>
> But the diagram shows gimple_lcx stopping at expand but continuing its
> lifetime through RTL passes (so gimple_lcx according to the diagram is
> _not_ destroyed by expand). So, I am left wondering if the bug is in the
> diagram or GCC.
On this build of GCC (standard Fedora 15 gcc package of 4.6.0), the
relevant part of cfgexpand.c looks like this:
struct rtl_opt_pass pass_expand =
{
{
RTL_PASS,
"expand", /* name */
[...snip...]
PROP_ssa | PROP_gimple_leh | PROP_cfg
| PROP_gimple_lcx, /* properties_required */
PROP_rtl, /* properties_provided */
PROP_ssa | PROP_trees, /* properties_destroyed */
[...snip...]
}
and gcc/tree-pass.h has:
#define PROP_trees \
(PROP_gimple_any | PROP_gimple_lcf | PROP_gimple_leh | PROP_gimple_lomp)
and that matches up with both the diagram, and the entry for "expand" in
the table below [1].
So it seems that the diagram is correctly accessing the
"properties_destroyed" data for the "expand" pass; does PROP_gimple_lcx
need to be added somewhere? (or should the diagram we taught to
specialcase some things, perhaps?)
Note that the diagram doesn't take the RTL_* enum into account.
FWIW, I added some more notes on passes here:
http://readthedocs.org/docs/gcc-python-plugin/en/latest/passes.html
which tries to summarize what the PROP_* flags mean (as I understand
them).
and there's a higher-level summary of GCC's insides (from the
perspective of a Python coder new to GCC) here:
http://readthedocs.org/docs/gcc-python-plugin/en/latest/gcc-overview.html
As before, caveat lector: I may have misunderstood things; I'm
relatively new to GCC.
Hope this is helpful
Dave
[1]
http://readthedocs.org/docs/gcc-python-plugin/en/latest/tables-of-passes.html#the-all-other-passes-catch-all
