On August 2, 2020 1:17:20 PM GMT+02:00, Sergei Trofimovich <sly...@gentoo.org>
wrote:
>From: Sergei Trofimovich <siarh...@google.com>
>
>r11-2447-g:1212cfad093 ("Improve var-tracking dataflow
>iteration order") changed 'in_pending' initialization
>from:
>
> in_pending = sbitmap_alloc (last_basic_block_for_fn (cfun));
> bitmap_ones (in_pending);
>
>to more complex partial bit population algorithm. Due to presence
>of uninitialized bits gcc started injecting extra debug entries
>in seemigly arbitrary locations and started failing stage2/stage3
>bootstrap comparison.
>
>valgrind detected unilitialized bits as:
>
> Conditional jump or move depends on uninitialised value(s)
> at 0xDBED3B: vt_find_locations() (var-tracking.c:7230)
> by 0xDBF2FB: variable_tracking_main_1() (var-tracking.c:10519)
> ...
> Uninitialised value was created by a heap allocation
> at 0x483779F: malloc (vg_replace_malloc.c:307)
> by 0x14EE80B: xmalloc (xmalloc.c:147)
> by 0x14911F9: sbitmap_alloc(unsigned int) (sbitmap.c:51)
> ...
>
>The fix explicitly initializes 'in_pending' bitmap with zeros.
OK and thanks for tracking this down. Guess the default bootstrap-debug hid
this issue for me.
Richard.
>gcc:
>
>2020-08-02 Sergei Trofimovich <siarh...@google.com>
>
> PR bootstrap96404
> * var-tracking.c (vt_find_locations): Fully initialize
> all 'in_pending' bits.
>
>Signed-off-by: Sergei Trofimovich <siarh...@google.com>
>---
> gcc/var-tracking.c | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/gcc/var-tracking.c b/gcc/var-tracking.c
>index 743f5dcecf6..52aea47a053 100644
>--- a/gcc/var-tracking.c
>+++ b/gcc/var-tracking.c
>@@ -7096,6 +7096,7 @@ vt_find_locations (void)
> in_worklist = sbitmap_alloc (last_basic_block_for_fn (cfun));
> in_pending = sbitmap_alloc (last_basic_block_for_fn (cfun));
> bitmap_clear (in_worklist);
>+ bitmap_clear (in_pending);
>
> /* We're performing the dataflow iteration independently over the
> toplevel SCCs plus leading non-cyclic entry blocks and separately
