On September 17, 2014 8:20:41 PM CEST, Jakub Jelinek <ja...@redhat.com> wrote:
>Hi!
>
>The following testcase fails on 4.9 branch (shows
>undesirable difference in *.optimized dump on the trunk, but
>doesn't report -fcompare-debug failure there, and in 4.8 is latent).
>The problem is that if we have a noreturn stmt followed by only
>debug stmt, fixup_noreturn_call will try to split_block after the
>noreturn call, but with -g0 there are never debug stmts and thus
>we would not split the block; that can lead to different order of bb
>predecessors, different order of PHI args etc.
>
>As nothing after noreturn call really matters, this patch if there are
>only debug stmts after noreturn call removes the debug stmts instead of
>the undesirable splitting of the block.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux on the trunk and
>on
>the 4.9 branch, ok for trunk/4.9 and eventually 4.8 too?
OK everywhere.
Thanks,
Richard.
>
>2014-09-17 Jakub Jelinek <ja...@redhat.com>
>
> PR debug/63284
> * tree-cfgcleanup.c (fixup_noreturn_call): Don't split block
> if there are only debug stmts after the noreturn call, instead
> remove the debug stmts.
>
> * gcc.dg/pr63284.c: New test.
>
>--- gcc/tree-cfgcleanup.c.jj 2014-09-01 13:33:11.000000000 +0200
>+++ gcc/tree-cfgcleanup.c 2014-09-17 11:01:53.448165423 +0200
>@@ -565,7 +565,20 @@ fixup_noreturn_call (gimple stmt)
>
> /* First split basic block if stmt is not last. */
> if (stmt != gsi_stmt (gsi_last_bb (bb)))
>- split_block (bb, stmt);
>+ {
>+ if (stmt == gsi_stmt (gsi_last_nondebug_bb (bb)))
>+ {
>+ /* Don't split if there are only debug stmts
>+ after stmt, that can result in -fcompare-debug
>+ failures. Remove the debug stmts instead,
>+ they should be all unreachable anyway. */
>+ gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
>+ for (gsi_next (&gsi); !gsi_end_p (gsi); )
>+ gsi_remove (&gsi, true);
>+ }
>+ else
>+ split_block (bb, stmt);
>+ }
>
> changed |= remove_fallthru_edge (bb->succs);
>
>--- gcc/testsuite/gcc.dg/pr63284.c.jj 2014-09-17 10:56:59.699677715
>+0200
>+++ gcc/testsuite/gcc.dg/pr63284.c 2014-09-17 10:56:39.000000000 +0200
>@@ -0,0 +1,42 @@
>+/* PR debug/63284 */
>+/* { dg-do compile } */
>+/* { dg-options "-O2 -fcompare-debug" } */
>+
>+int a[10], *b, *d, c, f;
>+int fn2 (void);
>+void fn3 (void);
>+void fn4 (int);
>+
>+static int
>+fn1 (int x)
>+{
>+ int e = a[0];
>+ if (e)
>+ return 1;
>+ if (b)
>+ switch (x)
>+ {
>+ case 1:
>+ if (d)
>+ e = fn2 ();
>+ else
>+ fn3 ();
>+ break;
>+ case 0:
>+ if (d)
>+ {
>+ fn3 ();
>+ if (c)
>+ fn4 (1);
>+ }
>+ else
>+ fn4 (0);
>+ }
>+ return e;
>+}
>+
>+void
>+fn6 (void)
>+{
>+ f = fn1 (0);
>+}
>
> Jakub
