/* 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, 2010, 201
+ 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 "tm.h"
#include "tree.h"
#include "flags.h"
-#include "rtl.h"
#include "tm_p.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
- B instead of creating B' for one destination if all edges into B are
- going to be threaded to a successor of B.
+ 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. We had code to do this at one time, but
+ I'm not convinced it is correct with the changes to avoid mucking up
+ the loop structure (which may cancel threading requests, thus a block
+ which we thought was going to become unreachable may still be reachable).
+ This code was also going to get ugly with the introduction of the ability
+ for a single jump thread request to bypass multiple blocks.
We further reduce the number of edges and statements we create by
not copying all the outgoing edges and the control statement in
its single successor. */
edge outgoing_edge;
+ edge intermediate_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. */
/* 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;
+
+/* When we start updating the CFG for threading, data necessary for jump
+ threading is attached to the AUX field for the incoming edge. Use these
+ macros to access the underlying structure attached to the AUX field. */
+#define THREAD_TARGET(E) ((edge *)(E)->aux)[0]
+#define THREAD_TARGET2(E) ((edge *)(E)->aux)[1]
+
+/* 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.
If DEST_BB is NULL, then remove all outgoing edges. */
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);
}
}
-/* Create a duplicate of BB which only reaches the destination of the edge
- stored in RD. Record the duplicate block in RD. */
+/* Create a duplicate of BB. Record the duplicate block in RD. */
static void
create_block_for_threading (basic_block bb, struct redirection_data *rd)
{
+ edge_iterator ei;
+ edge e;
+
/* 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);
+
+ FOR_EACH_EDGE (e, ei, rd->dup_block->succs)
+ e->aux = NULL;
/* Zero out the profile, since the block is unreachable for now. */
rd->dup_block->frequency = 0;
rd->dup_block->count = 0;
-
- /* The call to duplicate_block will copy everything, including the
- useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove
- the useless COND_EXPR or SWITCH_EXPR here rather than having a
- specialized block copier. We also remove all outgoing edges
- from the duplicate block. The appropriate edge will be created
- later. */
- 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 = ((struct redirection_data *)p)->outgoing_edge;
- return htab_hash_pointer (e);
+ 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 = ((struct redirection_data *)p1)->outgoing_edge;
- edge e2 = ((struct redirection_data *)p2)->outgoing_edge;
+ edge e1 = ((const struct redirection_data *)p1)->outgoing_edge;
+ edge e2 = ((const struct redirection_data *)p2)->outgoing_edge;
+ edge e3 = ((const struct redirection_data *)p1)->intermediate_edge;
+ edge e4 = ((const struct redirection_data *)p2)->intermediate_edge;
- return e1 == e2;
+ return e1 == e2 && e3 == e4;
}
/* Given an outgoing edge E lookup and return its entry in our hash table.
edges associated with E in the hash table. */
static struct redirection_data *
-lookup_redirection_data (edge e, edge incoming_edge, bool insert)
+lookup_redirection_data (edge e, 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 = xmalloc (sizeof (struct redirection_data));
- elt->outgoing_edge = e;
+ elt = XNEW (struct redirection_data);
+ elt->intermediate_edge = THREAD_TARGET2 (e) ? THREAD_TARGET (e) : NULL;
+ elt->outgoing_edge = THREAD_TARGET2 (e) ? THREAD_TARGET2 (e)
+ : THREAD_TARGET (e);
elt->dup_block = NULL;
- elt->do_not_duplicate = false;
elt->incoming_edges = NULL;
slot = htab_find_slot (redirection_data, elt, insert);
if (*slot == NULL)
{
*slot = (void *)elt;
- elt->incoming_edges = xmalloc (sizeof (struct el));
- elt->incoming_edges->e = incoming_edge;
+ elt->incoming_edges = XNEW (struct el);
+ elt->incoming_edges->e = e;
elt->incoming_edges->next = NULL;
return elt;
}
to the list of incoming edges associated with E. */
if (insert)
{
- struct el *el = xmalloc (sizeof (struct el));
+ struct el *el = XNEW (struct el);
el->next = elt->incoming_edges;
- el->e = incoming_edge;
+ el->e = e;
elt->incoming_edges = el;
}
}
}
+/* For each PHI in BB, copy the argument associated with SRC_E to TGT_E. */
+
+static void
+copy_phi_args (basic_block bb, edge src_e, edge tgt_e)
+{
+ gimple_stmt_iterator gsi;
+ int src_indx = src_e->dest_idx;
+
+ for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ {
+ gimple phi = gsi_stmt (gsi);
+ source_location locus = gimple_phi_arg_location (phi, src_indx);
+ add_phi_arg (phi, gimple_phi_arg_def (phi, src_indx), tgt_e, locus);
+ }
+}
+
+/* We have recently made a copy of ORIG_BB, including its outgoing
+ edges. The copy is NEW_BB. Every PHI node in every direct successor of
+ ORIG_BB has a new argument associated with edge from NEW_BB to the
+ successor. Initialize the PHI argument so that it is equal to the PHI
+ argument associated with the edge from ORIG_BB to the successor. */
+
+static void
+update_destination_phis (basic_block orig_bb, basic_block new_bb)
+{
+ edge_iterator ei;
+ edge e;
+
+ FOR_EACH_EDGE (e, ei, orig_bb->succs)
+ {
+ edge e2 = find_edge (new_bb, e->dest);
+ copy_phi_args (e->dest, e, e2);
+ }
+}
+
/* Given a duplicate block and its single destination (both stored
in RD). Create an edge between the duplicate and its single
destination.
destination. */
static void
-create_edge_and_update_destination_phis (struct redirection_data *rd)
+create_edge_and_update_destination_phis (struct redirection_data *rd,
+ basic_block bb)
{
- edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU);
- tree phi;
+ edge e = make_edge (bb, rd->outgoing_edge->dest, EDGE_FALLTHRU);
+
+ rescan_loop_exit (e, true, false);
+ e->probability = REG_BR_PROB_BASE;
+ e->count = bb->count;
+
+ if (rd->outgoing_edge->aux)
+ {
+ e->aux = (edge *) XNEWVEC (edge, 2);
+ THREAD_TARGET(e) = THREAD_TARGET (rd->outgoing_edge);
+ THREAD_TARGET2(e) = THREAD_TARGET2 (rd->outgoing_edge);
+ }
+ else
+ {
+ e->aux = NULL;
+ }
/* 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))
+ copy_phi_args (e->dest, rd->outgoing_edge, e);
+}
+
+/* Wire up the outgoing edges from the duplicate block and
+ update any PHIs as needed. */
+static void
+fix_duplicate_block_edges (struct redirection_data *rd,
+ struct local_info *local_info)
+{
+ /* If we were threading through an joiner block, then we want
+ to keep its control statement and redirect an outgoing edge.
+ Else we want to remove the control statement & edges, then create
+ a new outgoing edge. In both cases we may need to update PHIs. */
+ if (THREAD_TARGET2 (rd->incoming_edges->e))
+ {
+ edge victim;
+ edge e2;
+ edge e = rd->incoming_edges->e;
+
+ /* This updates the PHIs at the destination of the duplicate
+ block. */
+ update_destination_phis (local_info->bb, rd->dup_block);
+
+ /* Find the edge from the duplicate block to the block we're
+ threading through. That's the edge we want to redirect. */
+ victim = find_edge (rd->dup_block, THREAD_TARGET (e)->dest);
+ e2 = redirect_edge_and_branch (victim, THREAD_TARGET2 (e)->dest);
+
+ /* If we redirected the edge, then we need to copy PHI arguments
+ at the target. If the edge already existed (e2 != victim case),
+ then the PHIs in the target already have the correct arguments. */
+ if (e2 == victim)
+ copy_phi_args (e2->dest, THREAD_TARGET2 (e), e2);
+ }
+ else
{
- int indx = phi_arg_from_edge (phi, rd->outgoing_edge);
- add_phi_arg (&phi, PHI_ARG_DEF_TREE (phi, indx), e);
+ remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL);
+ create_edge_and_update_destination_phis (rd, rd->dup_block);
}
}
-
/* Hash table traversal callback routine to create duplicate blocks. */
static int
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->template_block, rd);
/* Go ahead and wire up outgoing edges and update PHIs for the duplicate
- block. */
- create_edge_and_update_destination_phis (rd);
+ block. */
+ fix_duplicate_block_edges (rd, local_info);
}
/* Keep walking the hash table. */
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 this is the template block halt the traversal after updating
+ it appropriately.
+
+ If we were threading through an joiner block, then we want
+ to keep its control statement and redirect an outgoing edge.
+ Else we want to remove the control statement & edges, then create
+ a new outgoing edge. In both cases we may need to update PHIs. */
if (rd->dup_block && rd->dup_block == local_info->template_block)
{
- create_edge_and_update_destination_phis (rd);
+ fix_duplicate_block_edges (rd, local_info);
return 0;
}
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 we are threading through a joiner block, then we have to
+ find the edge we want to redirect and update some PHI nodes. */
+ if (THREAD_TARGET2 (e))
+ {
+ edge e2;
- if (rd->dup_block)
+ /* We want to redirect the incoming edge to the joiner block (E)
+ to instead reach the duplicate of the joiner block. */
+ e2 = redirect_edge_and_branch (e, rd->dup_block);
+ flush_pending_stmts (e2);
+ }
+ else if (rd->dup_block)
{
edge e2;
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;
+
+ /* Excessive jump threading may make frequencies large enough so
+ the computation overflows. */
+ if (rd->dup_block->frequency < BB_FREQ_MAX * 2)
+ 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);
-
- if ((dump_file && (dump_flags & TDF_DETAILS))
- && e->src != e2->src)
- fprintf (dump_file, " basic block %d created\n", e2->src->index);
}
- 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);
+ /* Go ahead and clear E->aux. It's not needed anymore and failure
+ to clear it will cause all kinds of unpleasant problems later. */
+ free (e->aux);
+ e->aux = NULL;
- /* And fixup the flags on the single remaining edge. */
- EDGE_SUCC (local_info->bb, 0)->flags
- &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
- EDGE_SUCC (local_info->bb, 0)->flags |= EDGE_FALLTHRU;
- }
}
+
+ /* 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.
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;
struct local_info local_info;
-
- /* ALL indicates whether or not all incoming edges into BB should
- be threaded to a duplicate of BB. */
- bool all = true;
+ struct loop *loop = bb->loop_father;
/* 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
redirection_data_eq,
free);
- /* Record each unique threaded destination into a hash table for
- efficient lookups. */
- FOR_EACH_EDGE (e, ei, bb->preds)
+ /* 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)
{
- if (!e->aux)
- {
- all = false;
- }
+ e = loop_latch_edge (loop);
+
+ if (e->aux)
+ e2 = THREAD_TARGET (e);
else
- {
- edge e2 = e->aux;
+ e2 = NULL;
- /* Insert the outgoing edge into the hash table if it is not
- already in the hash table. */
- lookup_redirection_data (e2, e, true);
+ if (e2 && loop_exit_edge_p (loop, e2))
+ {
+ loop->header = NULL;
+ loop->latch = NULL;
}
}
- /* 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)
+ /* Record each unique threaded destination into a hash table for
+ efficient lookups. */
+ FOR_EACH_EDGE (e, ei, bb->preds)
{
- edge e = EDGE_PRED (bb, 0)->aux;
- lookup_redirection_data (e, NULL, false)->do_not_duplicate = true;
+ if (e->aux == NULL)
+ continue;
+
+ if (THREAD_TARGET2 (e))
+ e2 = THREAD_TARGET2 (e);
+ else
+ e2 = THREAD_TARGET (e);
+
+ 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)
+ || THREAD_TARGET2 (e))))
+ continue;
+
+ if (e->dest == e2->src)
+ update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e),
+ e->count, THREAD_TARGET (e));
+
+ /* Insert the outgoing edge into the hash table if it is not
+ already in the hash table. */
+ lookup_redirection_data (e, INSERT);
}
+ /* 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
the rest of the duplicates. */
local_info.template_block = NULL;
local_info.bb = bb;
+ local_info.jumps_threaded = false;
htab_traverse (redirection_data, create_duplicates, &local_info);
/* The template does not have an outgoing edge. Create that outgoing
/* 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 THREAD_TARGET (E). 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 = THREAD_TARGET (e);
+ struct redirection_data rd;
+
+ free (e->aux);
+ e->aux = NULL;
+
+ thread_stats.num_threaded_edges++;
+
+ if (single_pred_p (bb))
+ {
+ /* 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);
+
+ /* And fixup the flags on the single remaining edge. */
+ eto->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL);
+ eto->flags |= EDGE_FALLTHRU;
+
+ return bb;
+ }
+
+ /* Otherwise, we need to create a copy. */
+ if (e->dest == eto->src)
+ update_bb_profile_for_threading (bb, EDGE_FREQUENCY (e), e->count, eto);
+
+ rd.outgoing_edge = eto;
+
+ create_block_for_threading (bb, &rd);
+ remove_ctrl_stmt_and_useless_edges (rd.dup_block, NULL);
+ create_edge_and_update_destination_phis (&rd, rd.dup_block);
+
+ 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);
}
-/* Walk through all blocks and thread incoming edges to the block's
- destinations as requested. This is the only entry point into this
- file.
+/* 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
+};
+
+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;
+
+ /* This function assumes BB is a successor of LOOP->header.
+ If that is not the case return DOMST_NONDOMINATING which
+ is always safe. */
+ {
+ bool ok = false;
+
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ {
+ if (e->src == loop->header)
+ {
+ ok = true;
+ break;
+ }
+ }
+
+ if (!ok)
+ return DOMST_NONDOMINATING;
+ }
- Blocks which have one or more incoming edges have INCOMING_EDGE_THREADED
- set in the block's annotation.
+ 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);
+}
- Each edge that should be threaded has the new destination edge stored in
- the original edge's AUX field.
+/* 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. */
- This routine (or one of its callees) will clear INCOMING_EDGE_THREADED
- in the block annotations and the AUX field in the edges.
+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;
+ }
+ */
+
+ /* Threading through the header won't improve the code if the header has just
+ one successor. */
+ if (single_succ_p (header))
+ goto fail;
+
+ if (latch->aux)
+ {
+ if (THREAD_TARGET2 (latch))
+ goto fail;
+ tgt_edge = THREAD_TARGET (latch);
+ 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)
+ {
+ if (e == latch)
+ continue;
+
+ /* If latch is not threaded, and there is a header
+ edge that is not threaded, we would create loop
+ with multiple entries. */
+ goto fail;
+ }
+
+ if (THREAD_TARGET2 (e))
+ goto fail;
+ tgt_edge = THREAD_TARGET (e);
+ 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 (!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;
+ }
+
+ /* 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)
+ {
+ /* 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;
+
+ /* Thread the remaining edges through the former header. */
+ thread_block (header, false);
+ }
+ else
+ {
+ basic_block new_preheader;
+
+ /* 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;
+ }
+
+ /* 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;
+ }
+
+ return true;
+
+fail:
+ /* We failed to thread anything. Cancel the requests. */
+ FOR_EACH_EDGE (e, ei, header->preds)
+ {
+ free (e->aux);
+ e->aux = NULL;
+ }
+ return false;
+}
+
+/* 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 += 3)
+ {
+ edge e = VEC_index (edge, threaded_edges, i);
+ edge *x = (edge *) XNEWVEC (edge, 2);
+
+ e->aux = x;
+ THREAD_TARGET (e) = VEC_index (edge, threaded_edges, i + 1);
+ THREAD_TARGET2 (e) = VEC_index (edge, threaded_edges, i + 2);
+ 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)
+ {
+ free (e->aux);
+ e->aux = NULL;
+ }
+ }
+ else
+ bitmap_set_bit (threaded_blocks, i);
+ }
+ }
+ else
+ bitmap_copy (threaded_blocks, tmp);
+
+ BITMAP_FREE(tmp);
+}
+
+
+/* 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;
- FOR_EACH_BB (bb)
+ threaded_blocks = BITMAP_ALLOC (NULL);
+ memset (&thread_stats, 0, sizeof (thread_stats));
+
+ 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, edge e3)
+{
+ /* This can occur if we're jumping to a constant address or
+ or something similar. Just get out now. */
+ if (e2 == NULL)
+ return;
+
+ if (threaded_edges == NULL)
+ threaded_edges = VEC_alloc (edge, heap, 15);
+
+ if (dump_file && (dump_flags & TDF_DETAILS)
+ && e->dest != e2->src)
+ fprintf (dump_file,
+ " Registering jump thread around one or more intermediate blocks\n");
+
+ VEC_safe_push (edge, heap, threaded_edges, e);
+ VEC_safe_push (edge, heap, threaded_edges, e2);
+ VEC_safe_push (edge, heap, threaded_edges, e3);
+}
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