On Thu, 6 Aug 2020, Jakub Jelinek wrote:
> Hi!
>
> On the following testcase, if the IL before reassoc would be:
> ...
> <bb 4> [local count: 354334800]:
> if (x_3(D) == 2)
> goto <bb 7>; [34.00%]
> else
> goto <bb 5>; [66.00%]
>
> <bb 5> [local count: 233860967]:
> if (x_3(D) == 3)
> goto <bb 7>; [34.00%]
> else
> goto <bb 6>; [66.00%]
>
> <bb 6> [local count: 79512730]:
>
> <bb 7> [local count: 1073741824]:
> # prephitmp_7 = PHI <1(3), 1(4), 1(5), 1(2), 0(6)>
> then we'd optimize it properly, but as bb 5-7 is instead:
> <bb 5> [local count: 233860967]:
> if (x_3(D) == 3)
> goto <bb 6>; [34.00%]
> else
> goto <bb 7>; [66.00%]
>
> <bb 6> [local count: 79512730]:
>
> <bb 7> [local count: 1073741824]:
> # prephitmp_7 = PHI <1(3), 1(4), 0(5), 1(2), 1(6)>
> (i.e. the true/false edges on the last bb with condition swapped
> and ditto for the phi args), we don't recognize it. If bb 6
> is empty, there should be no functional difference between the two IL
> representations.
>
> This patch handles those special cases.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2020-08-06 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/96480
> * tree-ssa-reassoc.c (suitable_cond_bb): Add TEST_SWAPPED_P argument.
> If TEST_BB ends in cond and has one edge to *OTHER_BB and another
> through an empty bb to that block too, if PHI args don't match, retry
> them through the other path from TEST_BB.
> (maybe_optimize_range_tests): Adjust callers. Handle such LAST_BB
> through inversion of the condition.
>
> * gcc.dg/tree-ssa/pr96480.c: New test.
>
> --- gcc/tree-ssa-reassoc.c.jj 2020-07-30 15:04:38.000000000 +0200
> +++ gcc/tree-ssa-reassoc.c 2020-08-06 11:19:30.942825436 +0200
> @@ -4127,11 +4127,14 @@ final_range_test_p (gimple *stmt)
> of TEST_BB, and *OTHER_BB is either NULL and filled by the routine,
> or compared with to find a common basic block to which all conditions
> branch to if true resp. false. If BACKWARD is false, TEST_BB should
> - be the only predecessor of BB. */
> + be the only predecessor of BB. *TEST_SWAPPED_P is set to true if
> + TEST_BB is a bb ending in condition where the edge to non-*OTHER_BB
> + block points to an empty block that falls through into *OTHER_BB and
> + the phi args match that path. */
>
> static bool
> suitable_cond_bb (basic_block bb, basic_block test_bb, basic_block *other_bb,
> - bool backward)
> + bool *test_swapped_p, bool backward)
> {
> edge_iterator ei, ei2;
> edge e, e2;
> @@ -4196,6 +4199,7 @@ suitable_cond_bb (basic_block bb, basic_
> /* Now check all PHIs of *OTHER_BB. */
> e = find_edge (bb, *other_bb);
> e2 = find_edge (test_bb, *other_bb);
> + retry:;
> for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
> {
> gphi *phi = gsi.phi ();
> @@ -4221,11 +4225,52 @@ suitable_cond_bb (basic_block bb, basic_
> else
> {
> gimple *test_last = last_stmt (test_bb);
> - if (gimple_code (test_last) != GIMPLE_COND
> - && gimple_phi_arg_def (phi, e2->dest_idx)
> - == gimple_assign_lhs (test_last)
> - && (integer_zerop (gimple_phi_arg_def (phi, e->dest_idx))
> - || integer_onep (gimple_phi_arg_def (phi, e->dest_idx))))
> + if (gimple_code (test_last) == GIMPLE_COND)
> + {
> + if (backward ? e2->src != test_bb : e->src != bb)
> + return false;
> +
> + /* For last_bb, handle also:
> + if (x_3(D) == 3)
> + goto <bb 6>; [34.00%]
> + else
> + goto <bb 7>; [66.00%]
> +
> + <bb 6> [local count: 79512730]:
> +
> + <bb 7> [local count: 1073741824]:
> + # prephitmp_7 = PHI <1(3), 1(4), 0(5), 1(2), 1(6)>
> + where bb 7 is *OTHER_BB, but the PHI values from the
> + earlier bbs match the path through the empty bb
> + in between. */
> + edge e3;
> + if (backward)
> + e3 = EDGE_SUCC (test_bb,
> + e2 == EDGE_SUCC (test_bb, 0) ? 1 : 0);
> + else
> + e3 = EDGE_SUCC (bb,
> + e == EDGE_SUCC (bb, 0) ? 1 : 0);
> + if (empty_block_p (e3->dest)
> + && single_succ_p (e3->dest)
> + && single_succ (e3->dest) == *other_bb
> + && single_pred_p (e3->dest)
> + && single_succ_edge (e3->dest)->flags == EDGE_FALLTHRU)
> + {
> + if (backward)
> + e2 = single_succ_edge (e3->dest);
> + else
> + e = single_succ_edge (e3->dest);
> + if (test_swapped_p)
> + *test_swapped_p = true;
> + goto retry;
> + }
> + }
> + else if (gimple_phi_arg_def (phi, e2->dest_idx)
> + == gimple_assign_lhs (test_last)
> + && (integer_zerop (gimple_phi_arg_def (phi,
> + e->dest_idx))
> + || integer_onep (gimple_phi_arg_def (phi,
> + e->dest_idx))))
> continue;
> }
>
> @@ -4414,7 +4459,7 @@ maybe_optimize_range_tests (gimple *stmt
> while (single_pred_p (first_bb))
> {
> basic_block pred_bb = single_pred (first_bb);
> - if (!suitable_cond_bb (pred_bb, first_bb, &other_bb, true))
> + if (!suitable_cond_bb (pred_bb, first_bb, &other_bb, NULL, true))
> break;
> if (!no_side_effect_bb (first_bb))
> break;
> @@ -4444,7 +4489,8 @@ maybe_optimize_range_tests (gimple *stmt
> && gimple_code (stmt) == GIMPLE_COND
> && EDGE_COUNT (e->dest->succs) == 2)
> {
> - if (suitable_cond_bb (first_bb, e->dest, &other_bb, true))
> + if (suitable_cond_bb (first_bb, e->dest, &other_bb,
> + NULL, true))
> break;
> else
> other_bb = NULL;
> @@ -4472,7 +4518,7 @@ maybe_optimize_range_tests (gimple *stmt
> break;
> if (!single_pred_p (e->dest))
> break;
> - if (!suitable_cond_bb (e->dest, last_bb, &other_bb, false))
> + if (!suitable_cond_bb (e->dest, last_bb, &other_bb, NULL, false))
> break;
> if (!no_side_effect_bb (e->dest))
> break;
> @@ -4583,6 +4629,28 @@ maybe_optimize_range_tests (gimple *stmt
> bbinfo.safe_push (bb_ent);
> continue;
> }
> + else if (bb == last_bb)
> + {
> + /* For last_bb, handle also:
> + if (x_3(D) == 3)
> + goto <bb 6>; [34.00%]
> + else
> + goto <bb 7>; [66.00%]
> +
> + <bb 6> [local count: 79512730]:
> +
> + <bb 7> [local count: 1073741824]:
> + # prephitmp_7 = PHI <1(3), 1(4), 0(5), 1(2), 1(6)>
> + where bb 7 is OTHER_BB, but the PHI values from the
> + earlier bbs match the path through the empty bb
> + in between. */
> + bool test_swapped_p = false;
> + bool ok = suitable_cond_bb (single_pred (last_bb), last_bb,
> + &other_bb, &test_swapped_p, true);
> + gcc_assert (ok);
> + if (test_swapped_p)
> + e = EDGE_SUCC (bb, e == EDGE_SUCC (bb, 0) ? 1 : 0);
> + }
> /* Otherwise stmt is GIMPLE_COND. */
> code = gimple_cond_code (stmt);
> lhs = gimple_cond_lhs (stmt);
> --- gcc/testsuite/gcc.dg/tree-ssa/pr96480.c.jj 2020-08-05
> 16:08:30.625614787 +0200
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr96480.c 2020-08-05 16:02:32.498832099
> +0200
> @@ -0,0 +1,23 @@
> +/* PR tree-optimization/96480 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump " = _\[0-9]* <= 3;" "optimized" } } */
> +
> +int v[4];
> +
> +int
> +foo (int x)
> +{
> + int *p;
> + if (x == 0)
> + p = &v[0];
> + else if (x == 1)
> + p = &v[1];
> + else if (x == 2)
> + p = &v[2];
> + else if (x == 3)
> + p = &v[3];
> + else
> + p = &v[4];
> + return p != &v[4];
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
