/* Thread edges through blocks and update the control flow and SSA graphs.
- Copyright (C) 2004 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation,
+ Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
+the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful,
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
-along with GCC; see the file COPYING. If not, write to
-the Free Software Foundation, 59 Temple Place - Suite 330,
-Boston, MA 02111-1307, USA. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "ggc.h"
#include "basic-block.h"
#include "output.h"
-#include "errors.h"
#include "expr.h"
#include "function.h"
#include "diagnostic.h"
#include "tree-flow.h"
#include "tree-dump.h"
#include "tree-pass.h"
+#include "cfgloop.h"
/* Given a block B, update the CFG and SSA graph to reflect redirecting
one or more in-edges to B to instead reach the destination of an
7. Put the duplicated resources in B and all the B' blocks into SSA form.
Note that block duplication can be minimized by first collecting the
- the set of unique destination blocks that the incoming edges should
- be threaded to. Block duplication can be further minimized by using
+ set of unique destination blocks that the incoming edges should
+ be threaded to. Block duplication can be further minimized by using
B instead of creating B' for one destination if all edges into B are
- going to be threaded to a successor of B. */
+ going to be threaded to a successor of B.
+ We further reduce the number of edges and statements we create by
+ not copying all the outgoing edges and the control statement in
+ step #1. We instead create a template block without the outgoing
+ edges and duplicate the template. */
+
+
+/* Steps #5 and #6 of the above algorithm are best implemented by walking
+ all the incoming edges which thread to the same destination edge at
+ the same time. That avoids lots of table lookups to get information
+ for the destination edge.
+
+ To realize that implementation we create a list of incoming edges
+ which thread to the same outgoing edge. Thus to implement steps
+ #5 and #6 we traverse our hash table of outgoing edge information.
+ For each entry we walk the list of incoming edges which thread to
+ the current outgoing edge. */
+
+struct el
+{
+ edge e;
+ struct el *next;
+};
/* Main data structure recording information regarding B's duplicate
blocks. */
+/* We need to efficiently record the unique thread destinations of this
+ block and specific information associated with those destinations. We
+ may have many incoming edges threaded to the same outgoing edge. This
+ can be naturally implemented with a hash table. */
+
struct redirection_data
{
/* A duplicate of B with the trailing control statement removed and which
/* An outgoing edge from B. DUP_BLOCK will have OUTGOING_EDGE->dest as
its single successor. */
edge outgoing_edge;
+
+ /* A list of incoming edges which we want to thread to
+ OUTGOING_EDGE->dest. */
+ struct el *incoming_edges;
+
+ /* Flag indicating whether or not we should create a duplicate block
+ for this thread destination. This is only true if we are threading
+ all incoming edges and thus are using BB itself as a duplicate block. */
+ bool do_not_duplicate;
};
/* Main data structure to hold information for duplicates of BB. */
-static varray_type redirection_data;
+static htab_t redirection_data;
+
+/* Data structure of information to pass to hash table traversal routines. */
+struct local_info
+{
+ /* The current block we are working on. */
+ basic_block bb;
+
+ /* A template copy of BB with no outgoing edges or control statement that
+ we use for creating copies. */
+ basic_block template_block;
+
+ /* TRUE if we thread one or more jumps, FALSE otherwise. */
+ bool jumps_threaded;
+};
+
+/* Passes which use the jump threading code register jump threading
+ opportunities as they are discovered. We keep the registered
+ jump threading opportunities in this vector as edge pairs
+ (original_edge, target_edge). */
+static VEC(edge,heap) *threaded_edges;
+
+
+/* Jump threading statistics. */
+
+struct thread_stats_d
+{
+ unsigned long num_threaded_edges;
+};
+
+struct thread_stats_d thread_stats;
+
/* Remove the last statement in block BB if it is a control statement
Also remove all outgoing edges except the edge which reaches DEST_BB.
static void
remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb)
{
- block_stmt_iterator bsi;
+ gimple_stmt_iterator gsi;
edge e;
edge_iterator ei;
- bsi = bsi_last (bb);
+ gsi = gsi_last_bb (bb);
/* If the duplicate ends with a control statement, then remove it.
Note that if we are duplicating the template block rather than the
original basic block, then the duplicate might not have any real
statements in it. */
- if (!bsi_end_p (bsi)
- && bsi_stmt (bsi)
- && (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
- || TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR))
- bsi_remove (&bsi);
+ if (!gsi_end_p (gsi)
+ && gsi_stmt (gsi)
+ && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND
+ || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO
+ || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH))
+ gsi_remove (&gsi, true);
for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
{
if (e->dest != dest_bb)
- ssa_remove_edge (e);
+ remove_edge (e);
else
ei_next (&ei);
}
{
/* We can use the generic block duplication code and simply remove
the stuff we do not need. */
- rd->dup_block = duplicate_block (bb, NULL);
+ rd->dup_block = duplicate_block (bb, NULL, NULL);
/* Zero out the profile, since the block is unreachable for now. */
rd->dup_block->frequency = 0;
remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL);
}
+/* Hashing and equality routines for our hash table. */
+static hashval_t
+redirection_data_hash (const void *p)
+{
+ edge e = ((const struct redirection_data *)p)->outgoing_edge;
+ return e->dest->index;
+}
+
+static int
+redirection_data_eq (const void *p1, const void *p2)
+{
+ edge e1 = ((const struct redirection_data *)p1)->outgoing_edge;
+ edge e2 = ((const struct redirection_data *)p2)->outgoing_edge;
+
+ return e1 == e2;
+}
+
+/* Given an outgoing edge E lookup and return its entry in our hash table.
+
+ If INSERT is true, then we insert the entry into the hash table if
+ it is not already present. INCOMING_EDGE is added to the list of incoming
+ edges associated with E in the hash table. */
+
+static struct redirection_data *
+lookup_redirection_data (edge e, edge incoming_edge, enum insert_option insert)
+{
+ void **slot;
+ struct redirection_data *elt;
+
+ /* Build a hash table element so we can see if E is already
+ in the table. */
+ elt = XNEW (struct redirection_data);
+ elt->outgoing_edge = e;
+ elt->dup_block = NULL;
+ elt->do_not_duplicate = false;
+ elt->incoming_edges = NULL;
+
+ slot = htab_find_slot (redirection_data, elt, insert);
+
+ /* This will only happen if INSERT is false and the entry is not
+ in the hash table. */
+ if (slot == NULL)
+ {
+ free (elt);
+ return NULL;
+ }
+
+ /* This will only happen if E was not in the hash table and
+ INSERT is true. */
+ if (*slot == NULL)
+ {
+ *slot = (void *)elt;
+ elt->incoming_edges = XNEW (struct el);
+ elt->incoming_edges->e = incoming_edge;
+ elt->incoming_edges->next = NULL;
+ return elt;
+ }
+ /* E was in the hash table. */
+ else
+ {
+ /* Free ELT as we do not need it anymore, we will extract the
+ relevant entry from the hash table itself. */
+ free (elt);
+
+ /* Get the entry stored in the hash table. */
+ elt = (struct redirection_data *) *slot;
+
+ /* If insertion was requested, then we need to add INCOMING_EDGE
+ to the list of incoming edges associated with E. */
+ if (insert)
+ {
+ struct el *el = XNEW (struct el);
+ el->next = elt->incoming_edges;
+ el->e = incoming_edge;
+ elt->incoming_edges = el;
+ }
+
+ return elt;
+ }
+}
+
+/* Given a duplicate block and its single destination (both stored
+ in RD). Create an edge between the duplicate and its single
+ destination.
+
+ Add an additional argument to any PHI nodes at the single
+ destination. */
+
+static void
+create_edge_and_update_destination_phis (struct redirection_data *rd)
+{
+ edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU);
+ gimple_stmt_iterator gsi;
+
+ rescan_loop_exit (e, true, false);
+ e->probability = REG_BR_PROB_BASE;
+ e->count = rd->dup_block->count;
+ e->aux = rd->outgoing_edge->aux;
+
+ /* If there are any PHI nodes at the destination of the outgoing edge
+ from the duplicate block, then we will need to add a new argument
+ to them. The argument should have the same value as the argument
+ associated with the outgoing edge stored in RD. */
+ for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
+ {
+ gimple phi = gsi_stmt (gsi);
+ source_location locus;
+ int indx = rd->outgoing_edge->dest_idx;
+
+ locus = gimple_phi_arg_location (phi, indx);
+ add_phi_arg (phi, gimple_phi_arg_def (phi, indx), e, locus);
+ }
+}
+
+/* Hash table traversal callback routine to create duplicate blocks. */
+
+static int
+create_duplicates (void **slot, void *data)
+{
+ struct redirection_data *rd = (struct redirection_data *) *slot;
+ struct local_info *local_info = (struct local_info *)data;
+
+ /* If this entry should not have a duplicate created, then there's
+ nothing to do. */
+ if (rd->do_not_duplicate)
+ return 1;
+
+ /* Create a template block if we have not done so already. Otherwise
+ use the template to create a new block. */
+ if (local_info->template_block == NULL)
+ {
+ create_block_for_threading (local_info->bb, rd);
+ local_info->template_block = rd->dup_block;
+
+ /* We do not create any outgoing edges for the template. We will
+ take care of that in a later traversal. That way we do not
+ create edges that are going to just be deleted. */
+ }
+ else
+ {
+ create_block_for_threading (local_info->template_block, rd);
+
+ /* Go ahead and wire up outgoing edges and update PHIs for the duplicate
+ block. */
+ create_edge_and_update_destination_phis (rd);
+ }
+
+ /* Keep walking the hash table. */
+ return 1;
+}
+
+/* We did not create any outgoing edges for the template block during
+ block creation. This hash table traversal callback creates the
+ outgoing edge for the template block. */
+
+static int
+fixup_template_block (void **slot, void *data)
+{
+ struct redirection_data *rd = (struct redirection_data *) *slot;
+ struct local_info *local_info = (struct local_info *)data;
+
+ /* If this is the template block, then create its outgoing edges
+ and halt the hash table traversal. */
+ if (rd->dup_block && rd->dup_block == local_info->template_block)
+ {
+ create_edge_and_update_destination_phis (rd);
+ return 0;
+ }
+
+ return 1;
+}
+
+/* Hash table traversal callback to redirect each incoming edge
+ associated with this hash table element to its new destination. */
+
+static int
+redirect_edges (void **slot, void *data)
+{
+ struct redirection_data *rd = (struct redirection_data *) *slot;
+ struct local_info *local_info = (struct local_info *)data;
+ struct el *next, *el;
+
+ /* Walk over all the incoming edges associated associated with this
+ hash table entry. */
+ for (el = rd->incoming_edges; el; el = next)
+ {
+ edge e = el->e;
+
+ /* Go ahead and free this element from the list. Doing this now
+ avoids the need for another list walk when we destroy the hash
+ table. */
+ next = el->next;
+ free (el);
+
+ /* Go ahead and clear E->aux. It's not needed anymore and failure
+ to clear it will cause all kinds of unpleasant problems later. */
+ e->aux = NULL;
+
+ thread_stats.num_threaded_edges++;
+
+ if (rd->dup_block)
+ {
+ edge e2;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
+ e->src->index, e->dest->index, rd->dup_block->index);
+
+ rd->dup_block->count += e->count;
+ rd->dup_block->frequency += EDGE_FREQUENCY (e);
+ EDGE_SUCC (rd->dup_block, 0)->count += e->count;
+ /* Redirect the incoming edge to the appropriate duplicate
+ block. */
+ e2 = redirect_edge_and_branch (e, rd->dup_block);
+ gcc_assert (e == e2);
+ flush_pending_stmts (e2);
+ }
+ else
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
+ e->src->index, e->dest->index, local_info->bb->index);
+
+ /* We are using BB as the duplicate. Remove the unnecessary
+ outgoing edges and statements from BB. */
+ remove_ctrl_stmt_and_useless_edges (local_info->bb,
+ rd->outgoing_edge->dest);
+
+ /* Fixup the flags on the single remaining edge. */
+ single_succ_edge (local_info->bb)->flags
+ &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL);
+ single_succ_edge (local_info->bb)->flags |= EDGE_FALLTHRU;
+
+ /* And adjust count and frequency on BB. */
+ local_info->bb->count = e->count;
+ local_info->bb->frequency = EDGE_FREQUENCY (e);
+ }
+ }
+
+ /* Indicate that we actually threaded one or more jumps. */
+ if (rd->incoming_edges)
+ local_info->jumps_threaded = true;
+
+ return 1;
+}
+
+/* Return true if this block has no executable statements other than
+ a simple ctrl flow instruction. When the number of outgoing edges
+ is one, this is equivalent to a "forwarder" block. */
+
+static bool
+redirection_block_p (basic_block bb)
+{
+ gimple_stmt_iterator gsi;
+
+ /* Advance to the first executable statement. */
+ gsi = gsi_start_bb (bb);
+ while (!gsi_end_p (gsi)
+ && (gimple_code (gsi_stmt (gsi)) == GIMPLE_LABEL
+ || is_gimple_debug (gsi_stmt (gsi))
+ || gimple_nop_p (gsi_stmt (gsi))))
+ gsi_next (&gsi);
+
+ /* Check if this is an empty block. */
+ if (gsi_end_p (gsi))
+ return true;
+
+ /* Test that we've reached the terminating control statement. */
+ return gsi_stmt (gsi)
+ && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND
+ || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO
+ || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH);
+}
+
/* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB
is reached via one or more specific incoming edges, we know which
outgoing edge from BB will be traversed.
- We want to redirect those incoming edges to the target of the
+ We want to redirect those incoming edges to the target of the
appropriate outgoing edge. Doing so avoids a conditional branch
and may expose new optimization opportunities. Note that we have
to update dominator tree and SSA graph after such changes.
successor of BB. We then revector the incoming edges into BB to
the appropriate duplicate of BB.
- BB and its duplicates will have assignments to the same set of
- SSA_NAMEs. Right now, we just call into rewrite_ssa_into_ssa
- to update the SSA graph for those names.
+ If NOLOOP_ONLY is true, we only perform the threading as long as it
+ does not affect the structure of the loops in a nontrivial way. */
- We are also going to experiment with a true incremental update
- scheme for the duplicated resources. One of the interesting
- properties we can exploit here is that all the resources set
- in BB will have the same IDFS, so we have one IDFS computation
- per block with incoming threaded edges, which can lower the
- cost of the true incremental update algorithm. */
-
-static void
-thread_block (basic_block bb)
+static bool
+thread_block (basic_block bb, bool noloop_only)
{
/* E is an incoming edge into BB that we may or may not want to
redirect to a duplicate of BB. */
- edge e;
+ edge e, e2;
edge_iterator ei;
- basic_block template_block;
+ struct local_info local_info;
+ struct loop *loop = bb->loop_father;
/* ALL indicates whether or not all incoming edges into BB should
be threaded to a duplicate of BB. */
bool all = true;
- unsigned int i;
+ /* To avoid scanning a linear array for the element we need we instead
+ use a hash table. For normal code there should be no noticeable
+ difference. However, if we have a block with a large number of
+ incoming and outgoing edges such linear searches can get expensive. */
+ redirection_data = htab_create (EDGE_COUNT (bb->succs),
+ redirection_data_hash,
+ redirection_data_eq,
+ free);
+
+ /* If we thread the latch of the loop to its exit, the loop ceases to
+ exist. Make sure we do not restrict ourselves in order to preserve
+ this loop. */
+ if (loop->header == bb)
+ {
+ e = loop_latch_edge (loop);
+ e2 = (edge) e->aux;
- VARRAY_GENERIC_PTR_INIT (redirection_data, 2, "redirection data");
+ if (e2 && loop_exit_edge_p (loop, e2))
+ {
+ loop->header = NULL;
+ loop->latch = NULL;
+ }
+ }
- /* Look at each incoming edge into BB. Record each unique outgoing
- edge that we want to thread an incoming edge to. Also note if
- all incoming edges are threaded or not. */
+ /* Record each unique threaded destination into a hash table for
+ efficient lookups. */
FOR_EACH_EDGE (e, ei, bb->preds)
{
- if (!e->aux)
+ e2 = (edge) e->aux;
+
+ if (!e2
+ /* If NOLOOP_ONLY is true, we only allow threading through the
+ header of a loop to exit edges. */
+ || (noloop_only
+ && bb == bb->loop_father->header
+ && !loop_exit_edge_p (bb->loop_father, e2)))
{
all = false;
+ continue;
}
- else
- {
- unsigned int i;
- /* See if we can find an entry for the destination of this
- threaded edge that has already been recorded. */
- for (i = 0; i < VARRAY_ACTIVE_SIZE (redirection_data); i++)
- {
- struct redirection_data *rd;
- edge e2;
-
- rd = VARRAY_GENERIC_PTR (redirection_data, i);
- e2 = e->aux;
-
- if (e2->dest == rd->outgoing_edge->dest)
- break;
- }
+ update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e),
+ e->count, (edge) e->aux);
- /* If the loop did not terminate early, then we have a new
- destination for the incoming threaded edges. Record it. */
- if (i == VARRAY_ACTIVE_SIZE (redirection_data))
- {
- struct redirection_data *rd;
+ /* Insert the outgoing edge into the hash table if it is not
+ already in the hash table. */
+ lookup_redirection_data (e2, e, INSERT);
+ }
- rd = ggc_alloc_cleared (sizeof (struct redirection_data));
- rd->outgoing_edge = e->aux;
- VARRAY_PUSH_GENERIC_PTR (redirection_data, rd);
- }
- }
+ /* If we are going to thread all incoming edges to an outgoing edge, then
+ BB will become unreachable. Rather than just throwing it away, use
+ it for one of the duplicates. Mark the first incoming edge with the
+ DO_NOT_DUPLICATE attribute. */
+ if (all)
+ {
+ edge e = (edge) EDGE_PRED (bb, 0)->aux;
+ lookup_redirection_data (e, NULL, NO_INSERT)->do_not_duplicate = true;
}
- /* Now create duplicates of BB. Note that if all incoming edges are
- threaded, then BB is going to become unreachable. In that case
- we use BB for one of the duplicates rather than wasting memory
- duplicating BB. Thus the odd starting condition for the loop.
+ /* We do not update dominance info. */
+ free_dominance_info (CDI_DOMINATORS);
+
+ /* Now create duplicates of BB.
Note that for a block with a high outgoing degree we can waste
a lot of time and memory creating and destroying useless edges.
tail of the duplicate as well as all outgoing edges from the
duplicate. We then use that duplicate block as a template for
the rest of the duplicates. */
- template_block = NULL;
- for (i = (all ? 1 : 0); i < VARRAY_ACTIVE_SIZE (redirection_data); i++)
- {
- struct redirection_data *rd = VARRAY_GENERIC_PTR (redirection_data, i);
+ local_info.template_block = NULL;
+ local_info.bb = bb;
+ local_info.jumps_threaded = false;
+ htab_traverse (redirection_data, create_duplicates, &local_info);
- if (template_block == NULL)
- {
- create_block_for_threading (bb, rd);
- template_block = rd->dup_block;
- }
- else
- {
- create_block_for_threading (template_block, rd);
- }
- }
+ /* The template does not have an outgoing edge. Create that outgoing
+ edge and update PHI nodes as the edge's target as necessary.
+
+ We do this after creating all the duplicates to avoid creating
+ unnecessary edges. */
+ htab_traverse (redirection_data, fixup_template_block, &local_info);
+
+ /* The hash table traversals above created the duplicate blocks (and the
+ statements within the duplicate blocks). This loop creates PHI nodes for
+ the duplicated blocks and redirects the incoming edges into BB to reach
+ the duplicates of BB. */
+ htab_traverse (redirection_data, redirect_edges, &local_info);
+
+ /* Done with this block. Clear REDIRECTION_DATA. */
+ htab_delete (redirection_data);
+ redirection_data = NULL;
+
+ /* Indicate to our caller whether or not any jumps were threaded. */
+ return local_info.jumps_threaded;
+}
+
+/* Threads edge E through E->dest to the edge E->aux. Returns the copy
+ of E->dest created during threading, or E->dest if it was not necessary
+ to copy it (E is its single predecessor). */
+
+static basic_block
+thread_single_edge (edge e)
+{
+ basic_block bb = e->dest;
+ edge eto = (edge) e->aux;
+ struct redirection_data rd;
+
+ e->aux = NULL;
- /* Now created up edges from the duplicate blocks to their new
- destinations. Doing this as a separate loop after block creation
- allows us to avoid creating lots of useless edges. */
- for (i = (all ? 1 : 0); i < VARRAY_ACTIVE_SIZE (redirection_data); i++)
+ thread_stats.num_threaded_edges++;
+
+ if (single_pred_p (bb))
{
- struct redirection_data *rd = VARRAY_GENERIC_PTR (redirection_data, i);
- tree phi;
- edge e;
+ /* If BB has just a single predecessor, we should only remove the
+ control statements at its end, and successors except for ETO. */
+ remove_ctrl_stmt_and_useless_edges (bb, eto->dest);
- e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU);
+ /* And fixup the flags on the single remaining edge. */
+ eto->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL);
+ eto->flags |= EDGE_FALLTHRU;
- /* If there are any PHI nodes at the destination of the outgoing edge
- from the duplicate block, then we will need to add a new argument
- to them. The argument should have the same value as the argument
- associated with the outgoing edge stored in RD. */
- for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
- {
- int indx = phi_arg_from_edge (phi, rd->outgoing_edge);
- add_phi_arg (&phi, PHI_ARG_DEF_TREE (phi, indx), e);
- }
+ return bb;
}
- /* The loop above created the duplicate blocks (and the statements
- within the duplicate blocks). This loop creates PHI nodes for the
- duplicated blocks and redirects the incoming edges into BB to reach
- the duplicates of BB.
+ /* Otherwise, we need to create a copy. */
+ update_bb_profile_for_threading (bb, EDGE_FREQUENCY (e), e->count, eto);
+
+ rd.outgoing_edge = eto;
+
+ create_block_for_threading (bb, &rd);
+ create_edge_and_update_destination_phis (&rd);
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
+ e->src->index, e->dest->index, rd.dup_block->index);
+
+ rd.dup_block->count = e->count;
+ rd.dup_block->frequency = EDGE_FREQUENCY (e);
+ single_succ_edge (rd.dup_block)->count = e->count;
+ redirect_edge_and_branch (e, rd.dup_block);
+ flush_pending_stmts (e);
+
+ return rd.dup_block;
+}
+
+/* Callback for dfs_enumerate_from. Returns true if BB is different
+ from STOP and DBDS_CE_STOP. */
+
+static basic_block dbds_ce_stop;
+static bool
+dbds_continue_enumeration_p (const_basic_block bb, const void *stop)
+{
+ return (bb != (const_basic_block) stop
+ && bb != dbds_ce_stop);
+}
+
+/* Evaluates the dominance relationship of latch of the LOOP and BB, and
+ returns the state. */
+
+enum bb_dom_status
+{
+ /* BB does not dominate latch of the LOOP. */
+ DOMST_NONDOMINATING,
+ /* The LOOP is broken (there is no path from the header to its latch. */
+ DOMST_LOOP_BROKEN,
+ /* BB dominates the latch of the LOOP. */
+ DOMST_DOMINATING
+};
- Note that redirecting the edge will change e->pred_next, so we have
- to hold e->pred_next in a temporary.
+static enum bb_dom_status
+determine_bb_domination_status (struct loop *loop, basic_block bb)
+{
+ basic_block *bblocks;
+ unsigned nblocks, i;
+ bool bb_reachable = false;
+ edge_iterator ei;
+ edge e;
- If this turns out to be a performance problem, then we could create
- a list of incoming edges associated with each entry in
- REDIRECTION_DATA and walk over that list of edges instead. */
- for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
+#ifdef ENABLE_CHECKING
+ /* This function assumes BB is a successor of LOOP->header. */
{
- edge new_dest = e->aux;
+ bool ok = false;
- /* E was not threaded, then there is nothing to do. */
- if (!new_dest)
+ FOR_EACH_EDGE (e, ei, bb->preds)
{
- ei_next (&ei);
- continue;
+ if (e->src == loop->header)
+ {
+ ok = true;
+ break;
+ }
}
- /* Go ahead and clear E->aux. It's not needed anymore and failure
- to clear it will cause all kinds of unpleasant problems later. */
- e->aux = NULL;
+ gcc_assert (ok);
+ }
+#endif
+
+ if (bb == loop->latch)
+ return DOMST_DOMINATING;
+
+ /* Check that BB dominates LOOP->latch, and that it is back-reachable
+ from it. */
+
+ bblocks = XCNEWVEC (basic_block, loop->num_nodes);
+ dbds_ce_stop = loop->header;
+ nblocks = dfs_enumerate_from (loop->latch, 1, dbds_continue_enumeration_p,
+ bblocks, loop->num_nodes, bb);
+ for (i = 0; i < nblocks; i++)
+ FOR_EACH_EDGE (e, ei, bblocks[i]->preds)
+ {
+ if (e->src == loop->header)
+ {
+ free (bblocks);
+ return DOMST_NONDOMINATING;
+ }
+ if (e->src == bb)
+ bb_reachable = true;
+ }
+
+ free (bblocks);
+ return (bb_reachable ? DOMST_DOMINATING : DOMST_LOOP_BROKEN);
+}
- /* We know E is an edge we want to thread. Find the entry associated
- with E's new destination in the REDIRECTION_DATA array. */
- for (i = 0; i < VARRAY_ACTIVE_SIZE (redirection_data); i++)
- {
- struct redirection_data *rd;
+/* Thread jumps through the header of LOOP. Returns true if cfg changes.
+ If MAY_PEEL_LOOP_HEADERS is false, we avoid threading from entry edges
+ to the inside of the loop. */
+
+static bool
+thread_through_loop_header (struct loop *loop, bool may_peel_loop_headers)
+{
+ basic_block header = loop->header;
+ edge e, tgt_edge, latch = loop_latch_edge (loop);
+ edge_iterator ei;
+ basic_block tgt_bb, atgt_bb;
+ enum bb_dom_status domst;
+
+ /* We have already threaded through headers to exits, so all the threading
+ requests now are to the inside of the loop. We need to avoid creating
+ irreducible regions (i.e., loops with more than one entry block), and
+ also loop with several latch edges, or new subloops of the loop (although
+ there are cases where it might be appropriate, it is difficult to decide,
+ and doing it wrongly may confuse other optimizers).
+
+ We could handle more general cases here. However, the intention is to
+ preserve some information about the loop, which is impossible if its
+ structure changes significantly, in a way that is not well understood.
+ Thus we only handle few important special cases, in which also updating
+ of the loop-carried information should be feasible:
+
+ 1) Propagation of latch edge to a block that dominates the latch block
+ of a loop. This aims to handle the following idiom:
+
+ first = 1;
+ while (1)
+ {
+ if (first)
+ initialize;
+ first = 0;
+ body;
+ }
+
+ After threading the latch edge, this becomes
+
+ first = 1;
+ if (first)
+ initialize;
+ while (1)
+ {
+ first = 0;
+ body;
+ }
+
+ The original header of the loop is moved out of it, and we may thread
+ the remaining edges through it without further constraints.
+
+ 2) All entry edges are propagated to a single basic block that dominates
+ the latch block of the loop. This aims to handle the following idiom
+ (normally created for "for" loops):
+
+ i = 0;
+ while (1)
+ {
+ if (i >= 100)
+ break;
+ body;
+ i++;
+ }
+
+ This becomes
+
+ i = 0;
+ while (1)
+ {
+ body;
+ i++;
+ if (i >= 100)
+ break;
+ }
+ */
- rd = VARRAY_GENERIC_PTR (redirection_data, i);
+ /* Threading through the header won't improve the code if the header has just
+ one successor. */
+ if (single_succ_p (header))
+ goto fail;
- /* We have found the right entry if the outgoing edge in this
- entry matches E's new destination. Note that if we have not
- created a duplicate block (rd->dup_block is NULL), then we
- are going to re-use BB as a duplicate and we do not need
- to create PHI nodes or redirect the edge. */
- if (rd->outgoing_edge == new_dest && rd->dup_block)
+ if (latch->aux)
+ {
+ tgt_edge = (edge) latch->aux;
+ tgt_bb = tgt_edge->dest;
+ }
+ else if (!may_peel_loop_headers
+ && !redirection_block_p (loop->header))
+ goto fail;
+ else
+ {
+ tgt_bb = NULL;
+ tgt_edge = NULL;
+ FOR_EACH_EDGE (e, ei, header->preds)
+ {
+ if (!e->aux)
{
- edge e2;
+ if (e == latch)
+ continue;
- if (dump_file && (dump_flags & TDF_DETAILS))
- fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
- e->src->index, e->dest->index, rd->dup_block->index);
+ /* If latch is not threaded, and there is a header
+ edge that is not threaded, we would create loop
+ with multiple entries. */
+ goto fail;
+ }
- e2 = redirect_edge_and_branch (e, rd->dup_block);
- flush_pending_stmts (e2);
+ tgt_edge = (edge) e->aux;
+ atgt_bb = tgt_edge->dest;
+ if (!tgt_bb)
+ tgt_bb = atgt_bb;
+ /* Two targets of threading would make us create loop
+ with multiple entries. */
+ else if (tgt_bb != atgt_bb)
+ goto fail;
+ }
- if ((dump_file && (dump_flags & TDF_DETAILS))
- && e->src != e2->src)
- fprintf (dump_file, " basic block %d created\n",
- e2->src->index);
- break;
- }
+ if (!tgt_bb)
+ {
+ /* There are no threading requests. */
+ return false;
}
+
+ /* Redirecting to empty loop latch is useless. */
+ if (tgt_bb == loop->latch
+ && empty_block_p (loop->latch))
+ goto fail;
}
- /* If all the incoming edges where threaded, then we used BB as one
- of the duplicate blocks. We need to fixup BB in that case so that
- it no longer has a COND_EXPR or SWITCH_EXPR and reaches one destination
- unconditionally. */
- if (all)
+ /* The target block must dominate the loop latch, otherwise we would be
+ creating a subloop. */
+ domst = determine_bb_domination_status (loop, tgt_bb);
+ if (domst == DOMST_NONDOMINATING)
+ goto fail;
+ if (domst == DOMST_LOOP_BROKEN)
+ {
+ /* If the loop ceased to exist, mark it as such, and thread through its
+ original header. */
+ loop->header = NULL;
+ loop->latch = NULL;
+ return thread_block (header, false);
+ }
+
+ if (tgt_bb->loop_father->header == tgt_bb)
+ {
+ /* If the target of the threading is a header of a subloop, we need
+ to create a preheader for it, so that the headers of the two loops
+ do not merge. */
+ if (EDGE_COUNT (tgt_bb->preds) > 2)
+ {
+ tgt_bb = create_preheader (tgt_bb->loop_father, 0);
+ gcc_assert (tgt_bb != NULL);
+ }
+ else
+ tgt_bb = split_edge (tgt_edge);
+ }
+
+ if (latch->aux)
{
- struct redirection_data *rd;
+ /* First handle the case latch edge is redirected. */
+ loop->latch = thread_single_edge (latch);
+ gcc_assert (single_succ (loop->latch) == tgt_bb);
+ loop->header = tgt_bb;
- rd = VARRAY_GENERIC_PTR (redirection_data, 0);
+ /* Thread the remaining edges through the former header. */
+ thread_block (header, false);
+ }
+ else
+ {
+ basic_block new_preheader;
- if (dump_file && (dump_flags & TDF_DETAILS))
- fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
- EDGE_PRED (bb, 0)->src->index, bb->index,
- EDGE_SUCC (bb, 0)->dest->index);
+ /* Now consider the case entry edges are redirected to the new entry
+ block. Remember one entry edge, so that we can find the new
+ preheader (its destination after threading). */
+ FOR_EACH_EDGE (e, ei, header->preds)
+ {
+ if (e->aux)
+ break;
+ }
- remove_ctrl_stmt_and_useless_edges (bb, rd->outgoing_edge->dest);
- EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
- EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
+ /* The duplicate of the header is the new preheader of the loop. Ensure
+ that it is placed correctly in the loop hierarchy. */
+ set_loop_copy (loop, loop_outer (loop));
+
+ thread_block (header, false);
+ set_loop_copy (loop, NULL);
+ new_preheader = e->dest;
+
+ /* Create the new latch block. This is always necessary, as the latch
+ must have only a single successor, but the original header had at
+ least two successors. */
+ loop->latch = NULL;
+ mfb_kj_edge = single_succ_edge (new_preheader);
+ loop->header = mfb_kj_edge->dest;
+ latch = make_forwarder_block (tgt_bb, mfb_keep_just, NULL);
+ loop->header = latch->dest;
+ loop->latch = latch->src;
}
- /* Done with this block. Clear REDIRECTION_DATA. */
- VARRAY_CLEAR (redirection_data);
+ return true;
+
+fail:
+ /* We failed to thread anything. Cancel the requests. */
+ FOR_EACH_EDGE (e, ei, header->preds)
+ {
+ e->aux = NULL;
+ }
+ return false;
}
-/* Walk through all blocks and thread incoming edges to the block's
- destinations as requested. This is the only entry point into this
- file.
+/* Walk through the registered jump threads and convert them into a
+ form convenient for this pass.
+
+ Any block which has incoming edges threaded to outgoing edges
+ will have its entry in THREADED_BLOCK set.
+
+ Any threaded edge will have its new outgoing edge stored in the
+ original edge's AUX field.
+
+ This form avoids the need to walk all the edges in the CFG to
+ discover blocks which need processing and avoids unnecessary
+ hash table lookups to map from threaded edge to new target. */
+
+static void
+mark_threaded_blocks (bitmap threaded_blocks)
+{
+ unsigned int i;
+ bitmap_iterator bi;
+ bitmap tmp = BITMAP_ALLOC (NULL);
+ basic_block bb;
+ edge e;
+ edge_iterator ei;
+
+ for (i = 0; i < VEC_length (edge, threaded_edges); i += 2)
+ {
+ edge e = VEC_index (edge, threaded_edges, i);
+ edge e2 = VEC_index (edge, threaded_edges, i + 1);
+
+ e->aux = e2;
+ bitmap_set_bit (tmp, e->dest->index);
+ }
+
+ /* If optimizing for size, only thread through block if we don't have
+ to duplicate it or it's an otherwise empty redirection block. */
+ if (optimize_function_for_size_p (cfun))
+ {
+ EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi)
+ {
+ bb = BASIC_BLOCK (i);
+ if (EDGE_COUNT (bb->preds) > 1
+ && !redirection_block_p (bb))
+ {
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ e->aux = NULL;
+ }
+ else
+ bitmap_set_bit (threaded_blocks, i);
+ }
+ }
+ else
+ bitmap_copy (threaded_blocks, tmp);
- Blocks which have one or more incoming edges have INCOMING_EDGE_THREADED
- set in the block's annotation.
- this routine.
+ BITMAP_FREE(tmp);
+}
- Each edge that should be threaded has the new destination edge stored in
- the original edge's AUX field.
- This routine (or one of its callees) will clear INCOMING_EDGE_THREADED
- in the block annotations and the AUX field in the edges.
+/* Walk through all blocks and thread incoming edges to the appropriate
+ outgoing edge for each edge pair recorded in THREADED_EDGES.
It is the caller's responsibility to fix the dominance information
and rewrite duplicated SSA_NAMEs back into SSA form.
+ If MAY_PEEL_LOOP_HEADERS is false, we avoid threading edges through
+ loop headers if it does not simplify the loop.
+
Returns true if one or more edges were threaded, false otherwise. */
bool
-thread_through_all_blocks (void)
+thread_through_all_blocks (bool may_peel_loop_headers)
{
- basic_block bb;
bool retval = false;
+ unsigned int i;
+ bitmap_iterator bi;
+ bitmap threaded_blocks;
+ struct loop *loop;
+ loop_iterator li;
+
+ /* We must know about loops in order to preserve them. */
+ gcc_assert (current_loops != NULL);
+
+ if (threaded_edges == NULL)
+ return false;
+
+ threaded_blocks = BITMAP_ALLOC (NULL);
+ memset (&thread_stats, 0, sizeof (thread_stats));
- FOR_EACH_BB (bb)
+ mark_threaded_blocks (threaded_blocks);
+
+ initialize_original_copy_tables ();
+
+ /* First perform the threading requests that do not affect
+ loop structure. */
+ EXECUTE_IF_SET_IN_BITMAP (threaded_blocks, 0, i, bi)
{
- if (bb_ann (bb)->incoming_edge_threaded)
- {
- thread_block (bb);
- retval = true;
- bb_ann (bb)->incoming_edge_threaded = false;
- }
+ basic_block bb = BASIC_BLOCK (i);
+
+ if (EDGE_COUNT (bb->preds) > 0)
+ retval |= thread_block (bb, true);
+ }
+
+ /* Then perform the threading through loop headers. We start with the
+ innermost loop, so that the changes in cfg we perform won't affect
+ further threading. */
+ FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
+ {
+ if (!loop->header
+ || !bitmap_bit_p (threaded_blocks, loop->header->index))
+ continue;
+
+ retval |= thread_through_loop_header (loop, may_peel_loop_headers);
}
+
+ statistics_counter_event (cfun, "Jumps threaded",
+ thread_stats.num_threaded_edges);
+
+ free_original_copy_tables ();
+
+ BITMAP_FREE (threaded_blocks);
+ threaded_blocks = NULL;
+ VEC_free (edge, heap, threaded_edges);
+ threaded_edges = NULL;
+
+ if (retval)
+ loops_state_set (LOOPS_NEED_FIXUP);
+
return retval;
}
+
+/* Register a jump threading opportunity. We queue up all the jump
+ threading opportunities discovered by a pass and update the CFG
+ and SSA form all at once.
+
+ E is the edge we can thread, E2 is the new target edge, i.e., we
+ are effectively recording that E->dest can be changed to E2->dest
+ after fixing the SSA graph. */
+
+void
+register_jump_thread (edge e, edge e2)
+{
+ if (threaded_edges == NULL)
+ threaded_edges = VEC_alloc (edge, heap, 10);
+
+ VEC_safe_push (edge, heap, threaded_edges, e);
+ VEC_safe_push (edge, heap, threaded_edges, e2);
+}
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