#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
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:
+
+ <bb preheader>:
+ ...
+ goto <bb header>
+
+ <bb header>:
+ ivtmp_a = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
+ sum_a = PHI <sum_init (preheader), sum_b (latch)>
+ ...
+ use (ivtmp_a)
+ ...
+ sum_b = sum_a + sum_update
+ ...
+ if (ivtmp_a < n)
+ goto <bb latch>;
+ else
+ goto <bb exit>;
+
+ <bb latch>:
+ ivtmp_b = ivtmp_a + 1;
+ goto <bb header>
+
+ <bb exit>:
+ sum_z = PHI <sum_b (cond[1])>
+
+ [1] Where <bb cond> is single_pred (bb latch); In the simplest case,
+ that's <bb header>.
+
+ to:
+
+ <bb preheader>:
+ ...
+ goto <bb newheader>
+
+ <bb header>:
+ ivtmp_a = PHI <ivtmp_c (latch)>
+ sum_a = PHI <sum_c (latch)>
+ ...
+ use (ivtmp_a)
+ ...
+ sum_b = sum_a + sum_update
+ ...
+ goto <bb latch>;
+
+ <bb newheader>:
+ ivtmp_c = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
+ sum_c = PHI <sum_init (preheader), sum_b (latch)>
+ if (ivtmp_c < n + 1)
+ goto <bb header>;
+ else
+ goto <bb exit>;
+
+ <bb latch>:
+ ivtmp_b = ivtmp_a + 1;
+ goto <bb newheader>
+
+ <bb exit>:
+ sum_z = PHI <sum_c (newheader)>
+
+
+ In unified diff format:
+
+ <bb preheader>:
+ ...
+- goto <bb header>
++ goto <bb newheader>
+
+ <bb header>:
+- ivtmp_a = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
+- sum_a = PHI <sum_init (preheader), sum_b (latch)>
++ ivtmp_a = PHI <ivtmp_c (latch)>
++ sum_a = PHI <sum_c (latch)>
+ ...
+ use (ivtmp_a)
+ ...
+ sum_b = sum_a + sum_update
+ ...
+- if (ivtmp_a < n)
+- goto <bb latch>;
++ goto <bb latch>;
++
++ <bb newheader>:
++ ivtmp_c = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
++ sum_c = PHI <sum_init (preheader), sum_b (latch)>
++ if (ivtmp_c < n + 1)
++ goto <bb header>;
+ else
+ goto <bb exit>;
+
+ <bb latch>:
+ ivtmp_b = ivtmp_a + 1;
+- goto <bb header>
++ goto <bb newheader>
+
+ <bb exit>:
+- sum_z = PHI <sum_b (cond[1])>
++ sum_z = PHI <sum_c (newheader)>
+
+ 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 <gcond *> (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<basic_block> 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<edge_var_map> *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 <gcond *> (last_stmt (exit->src));
+ tree control = gimple_cond_lhs (cond_stmt);
+ gphi *phi = as_a <gphi *> (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:
+ <bb 6>:
+ # graphite_IV.5_46 = PHI <0(5), graphite_IV.5_47(11)>
+ <bb 7>:
+ _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,
/* 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)
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