Add transform_to_exit_first_loop_alt 2015-04-14 Tom de Vries PR tree-optimization/65443 * tree-parloops.c (replace_imm_uses, replace_uses_in_bb_by) (replace_uses_in_bbs_by, transform_to_exit_first_loop_alt) (try_transform_to_exit_first_loop_alt): New function. (transform_to_exit_first_loop): Use try_transform_to_exit_first_loop_alt. --- gcc/tree-parloops.c | 405 ++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 393 insertions(+), 12 deletions(-) diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c index 080d35e..8168632 100644 --- a/gcc/tree-parloops.c +++ b/gcc/tree-parloops.c @@ -78,6 +78,7 @@ along with GCC; see the file COPYING3. If not see #include "plugin-api.h" #include "ipa-ref.h" #include "cgraph.h" +#include "tree-ssa.h" /* This pass tries to distribute iterations of loops into several threads. The implementation is straightforward -- for each loop we test whether its @@ -1487,17 +1488,386 @@ create_loop_fn (location_t loc) return decl; } -/* Moves the exit condition of LOOP to the beginning of its header, and - duplicates the part of the last iteration that gets disabled to the - exit of the loop. NIT is the number of iterations of the loop - (used to initialize the variables in the duplicated part). +/* Replace uses of NAME by VAL in block BB. */ - TODO: the common case is that latch of the loop is empty and immediately - follows the loop exit. In this case, it would be better not to copy the - body of the loop, but only move the entry of the loop directly before the - exit check and increase the number of iterations of the loop by one. - This may need some additional preconditioning in case NIT = ~0. - REDUCTION_LIST describes the reductions in LOOP. */ +static void +replace_uses_in_bb_by (tree name, tree val, basic_block bb) +{ + gimple use_stmt; + imm_use_iterator imm_iter; + + FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, name) + { + if (gimple_bb (use_stmt) != bb) + continue; + + use_operand_p use_p; + FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter) + SET_USE (use_p, val); + } +} + +/* Replace uses of NAME by VAL in blocks BBS. */ + +static void +replace_uses_in_bbs_by (tree name, tree val, bitmap bbs) +{ + gimple use_stmt; + imm_use_iterator imm_iter; + + FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, name) + { + if (!bitmap_bit_p (bbs, gimple_bb (use_stmt)->index)) + continue; + + use_operand_p use_p; + FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter) + SET_USE (use_p, val); + } +} + +/* Do transformation from: + + : + ... + goto + + : + ivtmp_a = PHI + sum_a = PHI + ... + use (ivtmp_a) + ... + sum_b = sum_a + sum_update + ... + if (ivtmp_a < n) + goto ; + else + goto ; + + : + ivtmp_b = ivtmp_a + 1; + goto + + : + sum_z = PHI + + [1] Where is single_pred (bb latch); In the simplest case, + that's . + + to: + + : + ... + goto + + : + ivtmp_a = PHI + sum_a = PHI + ... + use (ivtmp_a) + ... + sum_b = sum_a + sum_update + ... + goto ; + + : + ivtmp_c = PHI + sum_c = PHI + if (ivtmp_c < n + 1) + goto ; + else + goto ; + + : + ivtmp_b = ivtmp_a + 1; + goto + + : + sum_z = PHI + + + In unified diff format: + + : + ... +- goto ++ goto + + : +- ivtmp_a = PHI +- sum_a = PHI ++ ivtmp_a = PHI ++ sum_a = PHI + ... + use (ivtmp_a) + ... + sum_b = sum_a + sum_update + ... +- if (ivtmp_a < n) +- goto ; ++ goto ; ++ ++ : ++ ivtmp_c = PHI ++ sum_c = PHI ++ if (ivtmp_c < n + 1) ++ goto ; + else + goto ; + + : + ivtmp_b = ivtmp_a + 1; +- goto ++ goto + + : +- sum_z = PHI ++ sum_z = PHI + + Note: the example does not show any virtual phis, but these are handled more + or less as reductions. + + + Moves the exit condition of LOOP to the beginning of its header. + REDUCTION_LIST describes the reductions in LOOP. BOUND is the new loop + bound. */ + +static void +transform_to_exit_first_loop_alt (struct loop *loop, + reduction_info_table_type *reduction_list, + tree bound) +{ + basic_block header = loop->header; + basic_block latch = loop->latch; + edge exit = single_dom_exit (loop); + basic_block exit_block = exit->dest; + gcond *cond_stmt = as_a (last_stmt (exit->src)); + tree control = gimple_cond_lhs (cond_stmt); + edge e; + + /* Gather the bbs dominated by the exit block. */ + bitmap exit_dominated = BITMAP_ALLOC (NULL); + bitmap_set_bit (exit_dominated, exit_block->index); + vec exit_dominated_vec + = get_dominated_by (CDI_DOMINATORS, exit_block); + + int i; + basic_block dom_bb; + FOR_EACH_VEC_ELT (exit_dominated_vec, i, dom_bb) + bitmap_set_bit (exit_dominated, dom_bb->index); + + exit_dominated_vec.release (); + + /* Create the new_header block. */ + basic_block new_header = split_block_before_cond_jump (exit->src); + edge split_edge = single_pred_edge (new_header); + + /* Redirect entry edge to new_header. */ + edge entry = loop_preheader_edge (loop); + e = redirect_edge_and_branch (entry, new_header); + gcc_assert (e == entry); + + /* Redirect post_inc_edge to new_header. */ + edge post_inc_edge = single_succ_edge (latch); + e = redirect_edge_and_branch (post_inc_edge, new_header); + gcc_assert (e == post_inc_edge); + + /* Redirect post_cond_edge to header. */ + edge post_cond_edge = single_pred_edge (latch); + e = redirect_edge_and_branch (post_cond_edge, header); + gcc_assert (e == post_cond_edge); + + /* Redirect split_edge to latch. */ + e = redirect_edge_and_branch (split_edge, latch); + gcc_assert (e == split_edge); + + /* Set the new loop bound. */ + gimple_cond_set_rhs (cond_stmt, bound); + + /* Repair the ssa. */ + vec *v = redirect_edge_var_map_vector (post_inc_edge); + edge_var_map *vm; + gphi_iterator gsi; + for (gsi = gsi_start_phis (header), i = 0; + !gsi_end_p (gsi) && v->iterate (i, &vm); + gsi_next (&gsi), i++) + { + gphi *phi = gsi.phi (); + tree res_a = PHI_RESULT (phi); + + /* Create new phi. */ + tree res_c = copy_ssa_name (res_a, phi); + gphi *nphi = create_phi_node (res_c, new_header); + + /* Replace ivtmp_a with ivtmp_c in condition 'if (ivtmp_a < n)'. */ + replace_uses_in_bb_by (res_a, res_c, new_header); + + /* Replace ivtmp/sum_b with ivtmp/sum_c in header phi. */ + add_phi_arg (phi, res_c, post_cond_edge, UNKNOWN_LOCATION); + + /* Replace sum_b with sum_c in exit phi. Loop-closed ssa does not hold + for virtuals, so we cannot get away with exit_block only. */ + tree res_b = redirect_edge_var_map_def (vm); + replace_uses_in_bbs_by (res_b, res_c, exit_dominated); + + struct reduction_info *red = reduction_phi (reduction_list, phi); + gcc_assert (virtual_operand_p (res_a) + || res_a == control + || red != NULL); + + if (red) + { + /* Register the new reduction phi. */ + red->reduc_phi = nphi; + gimple_set_uid (red->reduc_phi, red->reduc_version); + } + } + gcc_assert (gsi_end_p (gsi) && !v->iterate (i, &vm)); + BITMAP_FREE (exit_dominated); + + /* Set the preheader argument of the new phis to ivtmp/sum_init. */ + flush_pending_stmts (entry); + + /* Set the latch arguments of the new phis to ivtmp/sum_b. */ + flush_pending_stmts (post_inc_edge); + + /* Register the reduction exit phis. */ + for (gphi_iterator gsi = gsi_start_phis (exit_block); + !gsi_end_p (gsi); + gsi_next (&gsi)) + { + gphi *phi = gsi.phi (); + tree res_z = PHI_RESULT (phi); + if (virtual_operand_p (res_z)) + continue; + + tree res_c = PHI_ARG_DEF_FROM_EDGE (phi, exit); + gimple reduc_phi = SSA_NAME_DEF_STMT (res_c); + struct reduction_info *red = reduction_phi (reduction_list, reduc_phi); + if (red != NULL) + red->keep_res = phi; + } + + /* We're going to cancel the loop at the end of gen_parallel_loop, but until + then we're still using some fields, so only bother about fields that are + still used: header and latch. + The loop has a new header bb, so we update it. The latch bb stays the + same. */ + loop->header = new_header; + + /* Recalculate dominance info. */ + free_dominance_info (CDI_DOMINATORS); + calculate_dominance_info (CDI_DOMINATORS); +} + +/* Tries to moves the exit condition of LOOP to the beginning of its header + without duplication of the loop body. NIT is the number of iterations of the + loop. REDUCTION_LIST describes the reductions in LOOP. Return true if + transformation is successful. */ + +static bool +try_transform_to_exit_first_loop_alt (struct loop *loop, + reduction_info_table_type *reduction_list, + tree nit) +{ + /* Check whether the latch contains a single statement. */ + if (!gimple_seq_singleton_p (bb_seq (loop->latch))) + return true; + + /* Check whether the latch contains the loop iv increment. */ + edge back = single_succ_edge (loop->latch); + edge exit = single_dom_exit (loop); + gcond *cond_stmt = as_a (last_stmt (exit->src)); + tree control = gimple_cond_lhs (cond_stmt); + gphi *phi = as_a (SSA_NAME_DEF_STMT (control)); + tree inc_res = gimple_phi_arg_def (phi, back->dest_idx); + if (gimple_bb (SSA_NAME_DEF_STMT (inc_res)) != loop->latch) + return false; + + /* Check whether there's no code between the loop condition and the latch. */ + if (!single_pred_p (loop->latch) + || single_pred (loop->latch) != exit->src) + return false; + + tree alt_bound = NULL_TREE; + tree nit_type = TREE_TYPE (nit); + + /* Figure out whether nit + 1 overflows. */ + if (TREE_CODE (nit) == INTEGER_CST) + { + if (!tree_int_cst_equal (nit, TYPE_MAXVAL (nit_type))) + { + alt_bound = fold_build2_loc (UNKNOWN_LOCATION, PLUS_EXPR, nit_type, + nit, build_one_cst (nit_type)); + + gcc_assert (TREE_CODE (alt_bound) == INTEGER_CST); + } + else + { + /* Todo: Figure out if we can trigger this, if it's worth to handle + optimally, and if we can handle it optimally. */ + } + } + else + { + gcc_assert (TREE_CODE (nit) == SSA_NAME); + + gimple def = SSA_NAME_DEF_STMT (nit); + + if (def + && is_gimple_assign (def) + && gimple_assign_rhs_code (def) == PLUS_EXPR) + { + tree op1 = gimple_assign_rhs1 (def); + tree op2 = gimple_assign_rhs2 (def); + if (integer_minus_onep (op1)) + alt_bound = op2; + else if (integer_minus_onep (op2)) + alt_bound = op1; + } + + /* There is a number of test-cases for which we don't get an alt_bound + here: they're listed here, with the lhs of the last stmt as the nit: + + libgomp.graphite/force-parallel-1.c: + _21 = (signed long) N_6(D); + _19 = _21 + -1; + _7 = (unsigned long) _19; + + libgomp.graphite/force-parallel-2.c: + _33 = (signed long) N_9(D); + _16 = _33 + -1; + _37 = (unsigned long) _16; + + libgomp.graphite/force-parallel-5.c: + : + # graphite_IV.5_46 = PHI <0(5), graphite_IV.5_47(11)> + : + _33 = (unsigned long) graphite_IV.5_46; + + g++.dg/tree-ssa/pr34355.C: + _2 = (unsigned int) i_9; + _3 = 4 - _2; + + gcc.dg/pr53849.c: + _5 = d.0_11 + -2; + _18 = (unsigned int) _5; + + We will be able to handle some of these cases, if we can determine when + it's safe to look past casts. */ + } + + if (alt_bound == NULL_TREE) + return false; + + transform_to_exit_first_loop_alt (loop, reduction_list, alt_bound); + return true; +} + +/* Moves the exit condition of LOOP to the beginning of its header. NIT is the + number of iterations of the loop. REDUCTION_LIST describes the reductions in + LOOP. */ static void transform_to_exit_first_loop (struct loop *loop, @@ -1882,8 +2252,19 @@ gen_parallel_loop (struct loop *loop, /* Base all the induction variables in LOOP on a single control one. */ canonicalize_loop_ivs (loop, &nit, true); - /* Ensure that the exit condition is the first statement in the loop. */ - transform_to_exit_first_loop (loop, reduction_list, nit); + /* Ensure that the exit condition is the first statement in the loop. + The common case is that latch of the loop is empty (apart from the + increment) and immediately follows the loop exit test. Attempt to move the + entry of the loop directly before the exit check and increase the number of + iterations of the loop by one. */ + if (!try_transform_to_exit_first_loop_alt (loop, reduction_list, nit)) + { + /* Fall back on the method that handles more cases, but duplicates the + loop body: move the exit condition of LOOP to the beginning of its + header, and duplicate the part of the last iteration that gets disabled + to the exit of the loop. */ + transform_to_exit_first_loop (loop, reduction_list, nit); + } /* Generate initializations for reductions. */ if (reduction_list->elements () > 0) -- 1.9.1