On March 28, 2020 1:50:59 AM GMT+01:00, Jakub Jelinek <ja...@redhat.com> wrote:
>Hi!
>
>The following testcase FAILs with -fcompare-debug, because
>reassociate_bb
>mishandles the case when the last stmt in a bb has zero uses. In that
>case
>reassoc_remove_stmt (like gsi_remove) moves the iterator to the next
>stmt,
>i.e. gsi_end_p is true, which means the code sets the iterator back to
>gsi_last_bb. The problem is that the for loop does gsi_prev on that
>before
>handling the next statement, which means the former penultimate stmt,
>now
>last one, is not processed by reassociate_bb.
>Now, with -g, if there is at least one debug stmt at the end of the bb,
>reassoc_remove_stmt moves the iterator to that following debug stmt and
>we
>just do gsi_prev and continue with the former penultimate non-debug
>stmt,
>now last non-debug stmt.
>
>The following patch fixes that by not doing the gsi_prev in this case;
>there
>are too many continue; cases, so I didn't want to copy over the
>gsi_prev to
>all of them, so this patch uses a bool for that instead. The second
>gsi_end_p check isn't needed anymore, because when we don't do the
>undesirable gsi_prev after gsi = gsi_last_bb, the loop !gsi_end_p (gsi)
>condition will catch the removal of the very last stmt from a bb.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
>2020-03-28 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/94329
> * tree-ssa-reassoc.c (reassociate_bb): When calling
>reassoc_remove_stmt
> on the last stmt in a bb, make sure gsi_prev isn't done immediately
> after gsi_last_bb.
>
> * gfortran.dg/pr94329.f90: New test.
>
>--- gcc/tree-ssa-reassoc.c.jj 2020-03-17 13:50:52.319942549 +0100
>+++ gcc/tree-ssa-reassoc.c 2020-03-27 15:49:14.323217631 +0100
>@@ -6224,8 +6224,11 @@ reassociate_bb (basic_block bb)
> if (stmt && !gimple_visited_p (stmt))
> cfg_cleanup_needed |= maybe_optimize_range_tests (stmt);
>
>- for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
>+ bool do_prev = false;
>+ for (gsi = gsi_last_bb (bb);
>+ !gsi_end_p (gsi); do_prev ? gsi_prev (&gsi) : (void) 0)
> {
>+ do_prev = true;
> stmt = gsi_stmt (gsi);
>
> if (is_gimple_assign (stmt)
>@@ -6246,15 +6249,12 @@ reassociate_bb (basic_block bb)
> release_defs (stmt);
> /* We might end up removing the last stmt above which
> places the iterator to the end of the sequence.
>- Reset it to the last stmt in this case which might
>- be the end of the sequence as well if we removed
>- the last statement of the sequence. In which case
>- we need to bail out. */
>+ Reset it to the last stmt in this case and make sure
>+ we don't do gsi_prev in that case. */
> if (gsi_end_p (gsi))
> {
> gsi = gsi_last_bb (bb);
>- if (gsi_end_p (gsi))
>- break;
>+ do_prev = false;
> }
> }
> continue;
>--- gcc/testsuite/gfortran.dg/pr94329.f90.jj 2020-03-27
>15:54:46.453249143 +0100
>+++ gcc/testsuite/gfortran.dg/pr94329.f90 2020-03-27 15:54:23.474592894
>+0100
>@@ -0,0 +1,12 @@
>+! PR tree-optimization/94329
>+! { dg-do compile }
>+! { dg-options "-O1 -fno-tree-loop-optimize -fwrapv -fcompare-debug" }
>+
>+subroutine pr94329 (s, t)
>+ real :: s, t(:,:)
>+ do i = 1,3
>+ do j = 1,3
>+ s = t(i,j)
>+ end do
>+ end do
>+end
>
> Jakub
