On Fri, Jan 26, 2024 at 04:16:54PM -0500, Jason Merrill wrote:
> On 12/5/23 20:52, Lewis Hyatt wrote:
> > Hello-
> >
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105608
> >
> > There are two related issues here really, a regression since GCC 11 where we
> > can ICE after restoring a PCH, and a deeper issue with bogus locations
> > assigned to macros that were defined prior to restoring a PCH. This patch
> > fixes the ICE regression with a simple change, and I think it's appropriate
> > for GCC 14 as well as backport to 11, 12, 13. The bad locations (wrong, but
> > not generally causing an ICE, and mostly affecting only the output of
> > -Wunused-macros) are not as problematic, and will be harder to fix. I could
> > take a stab at that for GCC 15. In the meantime the patch adds XFAILed
> > tests for the wrong locations (as well as passing tests for the regression
> > fix). Does it look OK please? Bootstrap + regtest all languages on x86-64
> > Linux. Thanks!
>
> OK for trunk and branches, thanks!
>
Thanks for the review! That is all taken care of. I have one more request if
you don't mind please... There have been some further comments on the PR
indicating that the new xfailed testcase I added is failing in an unexpected
way on at least one architecture. To recap, the idea here was that
1) libcpp needs new logic to be able to output correct locations for this
case. That will be some new code that is suitable for stage 1, not now.
2) In the meantime, we fixed things up enough to avoid an ICE that showed up
in GCC 11, and added an xfailed testcase to remind about #1.
The problem is that, the reason that libcpp outputs the wrong locations, is
that it has always used a location from the old line_map instance to index
into the new line_map instance, and so the exact details of the wrong
locations it outputs depend on the state of those two line maps, which may
differ depending on system includes and things like that. So I was hoping to
make one further one-line change to libcpp, not yet to output correct
locations, but at least to output one which is the same always and doesn't
depend on random things. This would assign all restored macros to a
consistent location, one line following the #include that triggered the PCH
process. I think this probably shouldn't be backported but it would be nice
to get into GCC 14, while nothing critical, at least it would avoid the new
test failure that's being reported. But more generally, I think using a
location from a totally different line map is dangerous and could have worse
consequences that haven't been seen yet. Does it look OK please? Thanks!
-Lewis
[PATCH] libcpp: Stabilize the location for macros restored after PCH [PR105608]
libcpp currently lacks the infrastructure to assign correct locations to
macros that were defined prior to loading a PCH and then restored
afterwards. While I plan to address that for GCC 15, this one-line patch
improves things by using at least a valid location, even if it's not the
best one. Without this change, libcpp uses pfile->directive_line as the
location for the restored macros, but this location_t applies to the old
line map, not the one that was just restored from the PCH, so the resulting
location is unpredictable and depends on what was stored in the line maps
before. With this change, all restored macros get assigned locations at
line_table->highest_line, which is the first line after the #include that
triggered the PCH restore. A future patch will store the actual file name
and line number of the definition and then synthesize locations in the new
line map pointing to the right place.
libcpp/ChangeLog:
PR preprocessor/105608
* pch.cc (cpp_read_state): Set a valid location for restored
macros.
gcc/testsuite/ChangeLog:
PR preprocessor/105608
* g++.dg/pch/line-map-3.C: Adjust to expect the new location.
diff --git a/libcpp/pch.cc b/libcpp/pch.cc
index e156fe257b3..f2f74ed6ea9 100644
--- a/libcpp/pch.cc
+++ b/libcpp/pch.cc
@@ -838,7 +838,14 @@ cpp_read_state (cpp_reader *r, const char *name, FILE *f,
!= NULL)
{
_cpp_clean_line (r);
- if (!_cpp_create_definition (r, h, 0))
+
+ /* ??? Using r->line_table->highest_line is not ideal here, but we
+ do need to use some location that is relative to the new line
+ map just loaded, not the old one that was in effect when these
+ macros were lexed. The proper fix is to remember the file name
+ and line number where each macro was defined, and then add
+ these locations into the new line map. See PR105608. */
+ if (!_cpp_create_definition (r, h, r->line_table->highest_line))
abort ();
_cpp_pop_buffer (r);
}
diff --git a/gcc/testsuite/g++.dg/pch/line-map-3.C
b/gcc/testsuite/g++.dg/pch/line-map-3.C
index 3390d7adba2..1ebabd0a5bf 100644
--- a/gcc/testsuite/g++.dg/pch/line-map-3.C
+++ b/gcc/testsuite/g++.dg/pch/line-map-3.C
@@ -1,5 +1,7 @@
#define UNUSED_MACRO /* { dg-error "UNUSED_MACRO" "" { xfail *-*-* } } */
-#include "line-map-3.H" /* { dg-bogus "-:UNUSED_MACRO" "" { xfail *-*-* } } */
+#include "line-map-3.H"
+/* { dg-line wrong_line } */
+/* { dg-bogus "-:UNUSED_MACRO" "" { xfail *-*-* } wrong_line } */
/* { dg-do compile } */
/* { dg-additional-options "-Werror=unused-macros" } */
@@ -14,7 +16,7 @@
/* In PCH mode we also complain incorrectly about the command line macro
-Dwith_PCH
added by dejagnu; that warning would get suppressed if the macro location
were
correctly restored by libcpp to reflect that it was a command line macro.
*/
-/* { dg-bogus "-:with_PCH" "" { xfail *-*-* } 2 } */
+/* { dg-bogus "-:with_PCH" "" { xfail *-*-* } wrong_line } */
/* The reason we used -Werror was to prevent pch.exp from rerunning without
PCH;
in that case we would get unnecessary XPASS outputs since the test does work
