On Wed, 3 Mar 2021, Richard Biener wrote:
> On Wed, 3 Mar 2021, David Malcolm wrote:
>
> > On Wed, 2021-03-03 at 08:48 +0100, Richard Biener wrote:
> > > On Tue, 2 Mar 2021, Martin Sebor wrote:
> > >
> > > > On 3/2/21 9:52 AM, Jeff Law via Gcc-patches wrote:
> > > > >
> > > > >
> > > > > On 3/1/21 1:39 AM, Richard Biener wrote:
> > > > > > The default diagnostic tree printer relies on dump_generic_node
> > > > > > which
> > > > > > for some reason manages to clobber the diagnostic pretty-
> > > > > > printer state
> > > > > > so we see garbled diagnostics like
> > > > > >
> > > > > > /home/rguenther/src/trunk/gcc/calls.c: In function
> > > > > > 'expand_call':
> > > > > > D.6750.coeffs[0]'/home/rguenther/src/trunk/gcc/dojump.c:118:28:
> > > > > > warning:
> > > > > > may be used uninitialized in this function [-Wmaybe-
> > > > > > uninitialized]
> > > > > >
> > > > > > when the diagnostic is emitted by the LTO fronted. The
> > > > > > following
> > > > > > approach using a temporary pretty-printer for the
> > > > > > dump_generic_node
> > > > > > call fixes this for some unknown reason and we issue
> > > > > >
> > > > > > /home/rguenther/src/trunk/gcc/calls.c: In function
> > > > > > 'expand_call':
> > > > > > /home/rguenther/src/trunk/gcc/dojump.c:118:28: warning:
> > > > > > 'MEM[(struct
> > > > > > poly_int *)&save].D.6750.coeffs[0]' may be used uninitialized
> > > > > > in this
> > > > > > function [-Wmaybe-uninitialized]
> > > > > >
> > > > > > [LTO] Bootstrapped and tested on x86_64-unknown-linux-gnu, OK
> > > > > > for trunk?
> > > > > >
> > > > > > Thanks,
> > > > > > Richard.
> > > > > >
> > > > > > 2021-02-26 Richard Biener <rguent...@suse.de>
> > > > > >
> > > > > > PR middle-end/97855
> > > > > > * tree-diagnostic.c (default_tree_printer): Use a temporary
> > > > > > pretty-printer when formatting a tree via dump_generic_node.
> > > > > It'd be good to know why this helps, but I trust your judgment
> > > > > that this
> > > > > is an improvement.
> > > >
> > > > I don't know if it's related but pr98492 tracks a problem in the
> > > > C++
> > > > front end caused by reinitializing the pretty printer in a number
> > > > of
> > > > functions in cp/error.c. When one of these functions is called
> > > > while
> > > > the pretty printer is formatting something, the effect of
> > > > the reinitialization is to drop the already formatted contents
> > > > of the printer's buffer.
> > > >
> > > > IIRC, I tripped over this when working on the MEM_REF formatting
> > > > improvement for -Wuninitialized.
> > >
> > > I've poked quite a bit with breakpoints on suspicious pretty-printer
> > > functions and watch points on the pp state but found nothing in the
> > > case I was looking at (curiously also -Wuninitialized). But I also
> > > wasn't able to understand why the caller should work at all. And
> > > yes, the C/C++ tree printers also simply format to the passed
> > > pretty-printer...
> > >
> > > Hoping that David could shed some light on how this should play
> > > together.
> >
> > This looks very much like the issue I ran into in
> > c46d057f55748520e819dcd8e04bca71be9902b2 (and, in retrospect, that
> > commit may have just been papering over the problem).
> >
> > The issue there was that pp_printf is not reentrant - if a handler for
> > a pp_printf format code ends up making a nested call to pp_printf, I
> > got behavior that looks like what you're seeing.
> >
> > That said, I've been poring over the output in PR middle-end/97855 and
> > comparing it to the various pretty-printer usage in the tree, and I'm
> > not seeing anywhere where a pp_printf seems to be used when generating:
> > MEM[(struct poly_int *)&save + 8B].D.6750.coeffs[0]
>
> I think it's the D.6750 which is printed via
>
> else if (TREE_CODE (node) == DEBUG_EXPR_DECL)
> {
> if (flags & TDF_NOUID)
> pp_string (pp, "D#xxxx");
> else
> pp_printf (pp, "D#%i", DEBUG_TEMP_UID (node));
>
> because this is a DECL_DEBUG_EXPR. One could experiment with
> avoiding pp_printf in dump_decl_name.
>
> > Is there a minimal reproducer (or a .i file?)
>
> No, you need to do a LTO bootstrap, repeat the link step of
> for example cc1 with -v -save-temps and pick an ltrans invocation
> that exhibits the issue ...
>
> I can poke at the above tomorrow again. I suppose we could
> also add some checking-assert into the pp_printf code at
> the problematic place (or is any recursion bogus?) to catch
> the case with an ICE.
It ICEs _a_ _lot_.
diff --git a/gcc/pretty-print.c b/gcc/pretty-print.c
index ade1933f86a..7755157a7d7 100644
--- a/gcc/pretty-print.c
+++ b/gcc/pretty-print.c
@@ -1069,6 +1069,11 @@ static const char *get_end_url_string
(pretty_printer *);
void
pp_format (pretty_printer *pp, text_info *text)
{
+ /* pp_format is not reentrant. */
+ static bool in_pp_format;
+ gcc_checking_assert (!in_pp_format);
+ in_pp_format = true;
+
output_buffer *buffer = pp_buffer (pp);
const char *p;
const char **args;
@@ -1500,6 +1505,8 @@ pp_format (pretty_printer *pp, text_info *text)
buffer->line_length = old_line_length;
pp_wrapping_mode (pp) = old_wrapping_mode;
pp_clear_state (pp);
+
+ in_pp_format = false;
}
/* Format of a message pointed to by TEXT. */
testresult summary attached (but it passes bootstrap).
Richard.
p.xz
Description: test summary
