On Thu, 3 Dec 2015, Jakub Jelinek wrote:
> Hi!
>
> As mentioned in the PR, maybe_optimize_range_tests considers basic blocks
> with not just the final GIMPLE_COND (or for last_bb store feeding into PHI),
> but also assign stmts that don't trap, don't have side-effects and where
> the SSA_NAMEs they set are used only in their own bb.
> Now, if we decide to optimize some range test, we can change some conditions
> on previous bbs and that means we could execute some basic blocks that
> wouldn't be executed in the original program. As the stmts don't set
> anything used in other bbs, they are most likely dead after the
> optimization, but the problem on the testcase is that because of the
> condition changes in previous bb we end up with incorrect value range
> for some SSA_NAME(s). That can result in the miscompilation of the testcase
> on certain targets.
>
> Fixed by resetting the value range info of such SSA_NAMEs. I believe it
> shouldn't be a big deal, they will be mostly dead anyway.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2015-12-03 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/68671
> * tree-ssa-reassoc.c (maybe_optimize_range_tests): For basic
> blocks starting with the successor of first bb we've modified
> and ending with last_bb, reset value ranges of all integral
> SSA_NAMEs set in those basic blocks.
>
> * gcc.dg/pr68671.c: New test.
>
> --- gcc/tree-ssa-reassoc.c.jj 2015-11-18 11:22:51.000000000 +0100
> +++ gcc/tree-ssa-reassoc.c 2015-12-03 18:12:08.915210122 +0100
> @@ -3204,7 +3204,7 @@ maybe_optimize_range_tests (gimple *stmt
> any_changes = optimize_range_tests (ERROR_MARK, &ops);
> if (any_changes)
> {
> - unsigned int idx;
> + unsigned int idx, max_idx = 0;
> /* update_ops relies on has_single_use predicates returning the
> same values as it did during get_ops earlier. Additionally it
> never removes statements, only adds new ones and it should walk
> @@ -3220,6 +3220,7 @@ maybe_optimize_range_tests (gimple *stmt
> {
> tree new_op;
>
> + max_idx = idx;
> stmt = last_stmt (bb);
> new_op = update_ops (bbinfo[idx].op,
> (enum tree_code)
> @@ -3289,6 +3290,10 @@ maybe_optimize_range_tests (gimple *stmt
> && ops[bbinfo[idx].first_idx]->op != NULL_TREE)
> {
> gcond *cond_stmt = as_a <gcond *> (last_stmt (bb));
> +
> + if (idx > max_idx)
> + max_idx = idx;
> +
> if (integer_zerop (ops[bbinfo[idx].first_idx]->op))
> gimple_cond_make_false (cond_stmt);
> else if (integer_onep (ops[bbinfo[idx].first_idx]->op))
> @@ -3305,6 +3310,30 @@ maybe_optimize_range_tests (gimple *stmt
> if (bb == first_bb)
> break;
> }
> +
> + /* The above changes could result in basic blocks after the first
> + modified one, up to and including last_bb, to be executed even if
> + they would not be in the original program. If the value ranges of
> + assignment lhs' in those bbs were dependent on the conditions
> + guarding those basic blocks which now can change, the VRs might
> + be incorrect. As no_side_effect_bb should ensure those SSA_NAMEs
> + are only used within the same bb, it should be not a big deal if
> + we just reset all the VRs in those bbs. See PR68671. */
> + for (bb = last_bb, idx = 0; idx < max_idx; bb = single_pred (bb),
> idx++)
> + {
> + gimple_stmt_iterator gsi;
> + for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
> + {
> + gimple *g = gsi_stmt (gsi);
> + if (!is_gimple_assign (g))
> + continue;
> + tree lhs = gimple_assign_lhs (g);
> + if (TREE_CODE (lhs) != SSA_NAME)
> + continue;
> + if (INTEGRAL_TYPE_P (TREE_TYPE (lhs)))
> + SSA_NAME_RANGE_INFO (lhs) = NULL;
Please use
reset_flow_sensitive_info (lhs);
Ok with that change.
Thanks,
Richard.
> + }
> + }
> }
> }
>
> --- gcc/testsuite/gcc.dg/pr68671.c.jj 2015-12-03 18:19:24.769104484 +0100
> +++ gcc/testsuite/gcc.dg/pr68671.c 2015-12-03 18:19:07.000000000 +0100
> @@ -0,0 +1,23 @@
> +/* PR tree-optimization/68671 */
> +/* { dg-do run } */
> +/* { dg-options " -O2 -fno-tree-dce" } */
> +
> +volatile int a = -1;
> +volatile int b;
> +
> +static inline int
> +fn1 (signed char p1, int p2)
> +{
> + return (p1 < 0) || (p1 > (1 >> p2)) ? 0 : (p1 << 1);
> +}
> +
> +int
> +main ()
> +{
> + signed char c = a;
> + b = fn1 (c, 1);
> + c = ((128 | c) < 0 ? 1 : 0);
> + if (c != 1)
> + __builtin_abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
