/* Thread edges through blocks and update the control flow and SSA graphs.
- Copyright (C) 2004 Free Software Foundation, Inc.
+ Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc.
This file is part of GCC.
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. */
+the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+Boston, MA 02110-1301, USA. */
#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
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
+ 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;
-
-/* For each PHI node in BB, find or create a PHI node in NEW_BB for the
- same PHI_RESULT. Add an argument to the PHI node in NEW_BB which
- corresponds to the same PHI argument associated with edge E in BB. */
+static htab_t redirection_data;
-static void
-copy_phis_to_block (basic_block new_bb, basic_block bb, edge e)
+/* Data structure of information to pass to hash table traversal routines. */
+struct local_info
{
- tree phi, arg;
+ /* The current block we are working on. */
+ basic_block bb;
- /* Walk over every PHI in BB. */
- for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- {
- tree new_phi;
+ /* A template copy of BB with no outgoing edges or control statement that
+ we use for creating copies. */
+ basic_block template_block;
- /* First try to find a PHI node in NEW_BB which has the same
- PHI_RESULT as the PHI from BB we are currently processing. */
- for (new_phi = phi_nodes (new_bb); new_phi;
- new_phi = PHI_CHAIN (new_phi))
- if (PHI_RESULT (new_phi) == PHI_RESULT (phi))
- break;
+ /* TRUE if we thread one or more jumps, FALSE otherwise. */
+ bool jumps_threaded;
+};
- /* If we did not find a suitable PHI in NEW_BB, create one. */
- if (!new_phi)
- new_phi = create_phi_node (PHI_RESULT (phi), new_bb);
+/* 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;
- /* Extract the argument corresponding to E from the current PHI
- node in BB. */
- arg = PHI_ARG_DEF_TREE (phi, phi_arg_from_edge (phi, e));
- /* Now add that same argument to the new PHI node in block NEW_BB. */
- add_phi_arg (&new_phi, arg, e);
- }
-}
+/* 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 (!bsi_end_p (bsi)
&& bsi_stmt (bsi)
&& (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
+ || TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
|| TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR))
- bsi_remove (&bsi);
+ bsi_remove (&bsi, 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 = ((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;
+
+ 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);
+ tree phi;
+
+ e->probability = REG_BR_PROB_BASE;
+ e->count = rd->dup_block->count;
+
+ /* 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 = rd->outgoing_edge->dest_idx;
+ add_phi_arg (phi, PHI_ARG_DEF (phi, indx), e);
+ }
+}
+
+/* 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;
+}
+
+/* Not all jump threading requests are useful. In particular some
+ jump threading requests can create irreducible regions which are
+ undesirable.
+
+ This routine will examine the BB's incoming edges for jump threading
+ requests which, if acted upon, would create irreducible regions. Any
+ such jump threading requests found will be pruned away. */
+
+static void
+prune_undesirable_thread_requests (basic_block bb)
+{
+ edge e;
+ edge_iterator ei;
+ bool may_create_irreducible_region = false;
+ unsigned int num_outgoing_edges_into_loop = 0;
+
+ /* For the heuristics below, we need to know if BB has more than
+ one outgoing edge into a loop. */
+ FOR_EACH_EDGE (e, ei, bb->succs)
+ num_outgoing_edges_into_loop += ((e->flags & EDGE_LOOP_EXIT) == 0);
+
+ if (num_outgoing_edges_into_loop > 1)
+ {
+ edge backedge = NULL;
+
+ /* Consider the effect of threading the edge (0, 1) to 2 on the left
+ CFG to produce the right CFG:
+
+
+ 0 0
+ | |
+ 1<--+ 2<--------+
+ / \ | | |
+ 2 3 | 4<----+ |
+ \ / | / \ | |
+ 4---+ E 1-- | --+
+ | | |
+ E 3---+
+
+
+ Threading the (0, 1) edge to 2 effectively creates two loops
+ (2, 4, 1) and (4, 1, 3) which are neither disjoint nor nested.
+ This is not good.
+
+ However, we do need to be able to thread (0, 1) to 2 or 3
+ in the left CFG below (which creates the middle and right
+ CFGs with nested loops).
+
+ 0 0 0
+ | | |
+ 1<--+ 2<----+ 3<-+<-+
+ /| | | | | | |
+ 2 | | 3<-+ | 1--+ |
+ \| | | | | | |
+ 3---+ 1--+--+ 2-----+
+
+
+ A safe heuristic appears to be to only allow threading if BB
+ has a single incoming backedge from one of its direct successors. */
+
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ {
+ if (e->flags & EDGE_DFS_BACK)
+ {
+ if (backedge)
+ {
+ backedge = NULL;
+ break;
+ }
+ else
+ {
+ backedge = e;
+ }
+ }
+ }
+
+ if (backedge && find_edge (bb, backedge->src))
+ ;
+ else
+ may_create_irreducible_region = true;
+ }
+ else
+ {
+ edge dest = NULL;
+
+ /* If we thread across the loop entry block (BB) into the
+ loop and BB is still reached from outside the loop, then
+ we would create an irreducible CFG. Consider the effect
+ of threading the edge (1, 4) to 5 on the left CFG to produce
+ the right CFG
+
+ 0 0
+ / \ / \
+ 1 2 1 2
+ \ / | |
+ 4<----+ 5<->4
+ / \ | |
+ E 5---+ E
+
+
+ Threading the (1, 4) edge to 5 creates two entry points
+ into the loop (4, 5) (one from block 1, the other from
+ block 2). A classic irreducible region.
+
+ So look at all of BB's incoming edges which are not
+ backedges and which are not threaded to the loop exit.
+ If that subset of incoming edges do not all thread
+ to the same block, then threading any of them will create
+ an irreducible region. */
+
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ {
+ edge e2;
+
+ /* We ignore back edges for now. This may need refinement
+ as threading a backedge creates an inner loop which
+ we would need to verify has a single entry point.
+
+ If all backedges thread to new locations, then this
+ block will no longer have incoming backedges and we
+ need not worry about creating irreducible regions
+ by threading through BB. I don't think this happens
+ enough in practice to worry about it. */
+ if (e->flags & EDGE_DFS_BACK)
+ continue;
+
+ /* If the incoming edge threads to the loop exit, then it
+ is clearly safe. */
+ e2 = e->aux;
+ if (e2 && (e2->flags & EDGE_LOOP_EXIT))
+ continue;
+
+ /* E enters the loop header and is not threaded. We can
+ not allow any other incoming edges to thread into
+ the loop as that would create an irreducible region. */
+ if (!e2)
+ {
+ may_create_irreducible_region = true;
+ break;
+ }
+
+ /* We know that this incoming edge threads to a block inside
+ the loop. This edge must thread to the same target in
+ the loop as any previously seen threaded edges. Otherwise
+ we will create an irreducible region. */
+ if (!dest)
+ dest = e2;
+ else if (e2 != dest)
+ {
+ may_create_irreducible_region = true;
+ break;
+ }
+ }
+ }
+
+ /* If we might create an irreducible region, then cancel any of
+ the jump threading requests for incoming edges which are
+ not backedges and which do not thread to the exit block. */
+ if (may_create_irreducible_region)
+ {
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ {
+ edge e2;
+
+ /* Ignore back edges. */
+ if (e->flags & EDGE_DFS_BACK)
+ continue;
+
+ e2 = e->aux;
+
+ /* If this incoming edge was not threaded, then there is
+ nothing to do. */
+ if (!e2)
+ continue;
+
+ /* If this incoming edge threaded to the loop exit,
+ then it can be ignored as it is safe. */
+ if (e2->flags & EDGE_LOOP_EXIT)
+ continue;
+
+ if (e2)
+ {
+ /* This edge threaded into the loop and the jump thread
+ request must be cancelled. */
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, " Not threading jump %d --> %d to %d\n",
+ e->src->index, e->dest->index, e2->dest->index);
+ e->aux = NULL;
+ }
+ }
+ }
+}
+
+/* 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);
+ 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);
+
+ /* And 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;
+ }
+ }
+
+ /* 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)
+{
+ block_stmt_iterator bsi;
+
+ /* Advance to the first executable statement. */
+ bsi = bsi_start (bb);
+ while (!bsi_end_p (bsi)
+ && (TREE_CODE (bsi_stmt (bsi)) == LABEL_EXPR
+ || IS_EMPTY_STMT (bsi_stmt (bsi))))
+ bsi_next (&bsi);
+
+ /* Check if this is an empty block. */
+ if (bsi_end_p (bsi))
+ return true;
+
+ /* Test that we've reached the terminating control statement. */
+ return bsi_stmt (bsi)
+ && (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
+ || TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
+ || TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR);
+}
+
/* 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.
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.
+ SSA_NAMEs. Right now, we just call into update_ssa to update the
+ SSA graph for those names.
We are also going to experiment with a true incremental update
scheme for the duplicated resources. One of the interesting
per block with incoming threaded edges, which can lower the
cost of the true incremental update algorithm. */
-static void
+static bool
thread_block (basic_block bb)
{
/* E is an incoming edge into BB that we may or may not want to
redirect to a duplicate of BB. */
edge e;
edge_iterator ei;
- basic_block template_block;
+ struct local_info local_info;
+
+ /* FOUND_BACKEDGE indicates that we found an incoming backedge
+ into BB, in which case we may ignore certain jump threads
+ to avoid creating irreducible regions. */
+ bool found_backedge = false;
/* ALL indicates whether or not all incoming edges into BB should
be threaded to a duplicate of BB. */
bool all = true;
- unsigned int i;
+ /* If optimizing for size, only thread this block if we don't have
+ to duplicate it or it's an otherwise empty redirection block. */
+ if (optimize_size
+ && EDGE_COUNT (bb->preds) > 1
+ && !redirection_block_p (bb))
+ {
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ e->aux = NULL;
+ return false;
+ }
- VARRAY_GENERIC_PTR_INIT (redirection_data, 2, "redirection data");
+ /* 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);
- /* 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. */
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ found_backedge |= ((e->flags & EDGE_DFS_BACK) != 0);
+
+ /* If BB has incoming backedges, then threading across BB might
+ introduce an irreducible region, which would be undesirable
+ as that inhibits various optimizations later. Prune away
+ any jump threading requests which we know will result in
+ an irreducible region. */
+ if (found_backedge)
+ prune_undesirable_thread_requests (bb);
+
+ /* Record each unique threaded destination into a hash table for
+ efficient lookups. */
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (!e->aux)
}
else
{
- unsigned int i;
+ edge e2 = e->aux;
+ update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e),
+ e->count, e->aux);
- /* 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;
- }
-
- /* 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;
-
- rd = ggc_alloc_cleared (sizeof (struct redirection_data));
- rd->outgoing_edge = e->aux;
- VARRAY_PUSH_GENERIC_PTR (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);
}
}
- /* 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.
+ /* 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_PRED (bb, 0)->aux;
+ lookup_redirection_data (e, NULL, NO_INSERT)->do_not_duplicate = true;
+ }
+
+ /* 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);
- }
- }
-
- /* 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++)
- {
- struct redirection_data *rd = VARRAY_GENERIC_PTR (redirection_data, i);
- tree phi;
- edge e;
-
- e = make_edge (rd->dup_block, rd->outgoing_edge->dest, 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);
- }
- }
-
- /* 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.
-
- Note that redirecting the edge will change e->pred_next, so we have
- to hold e->pred_next in a temporary.
+ /* The template does not have an outgoing edge. Create that outgoing
+ edge and update PHI nodes as the edge's target as necessary.
- 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)); )
- {
- edge new_dest = e->aux;
+ We do this after creating all the duplicates to avoid creating
+ unnecessary edges. */
+ htab_traverse (redirection_data, fixup_template_block, &local_info);
- /* E was not threaded, then there is nothing to do. */
- if (!new_dest)
- {
- ei_next (&ei);
- continue;
- }
+ /* 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);
- /* 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;
+ /* Done with this block. Clear REDIRECTION_DATA. */
+ htab_delete (redirection_data);
+ redirection_data = NULL;
- /* 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;
+ /* Indicate to our caller whether or not any jumps were threaded. */
+ return local_info.jumps_threaded;
+}
- rd = VARRAY_GENERIC_PTR (redirection_data, i);
+/* Walk through the registered jump threads and convert them into a
+ form convenient for this pass.
- /* 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)
- {
- edge e2;
- copy_phis_to_block (rd->dup_block, bb, e);
+ Any block which has incoming edges threaded to outgoing edges
+ will have its entry in THREADED_BLOCK set.
- 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);
+ Any threaded edge will have its new outgoing edge stored in the
+ original edge's AUX field.
- e2 = redirect_edge_and_branch (e, rd->dup_block);
- PENDING_STMT (e2) = NULL;
+ 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. */
- if ((dump_file && (dump_flags & TDF_DETAILS))
- && e->src != e2->src)
- fprintf (dump_file, " basic block %d created\n",
- e2->src->index);
- break;
- }
- }
- }
+static void
+mark_threaded_blocks (bitmap threaded_blocks)
+{
+ unsigned int i;
- /* 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)
+ for (i = 0; i < VEC_length (edge, threaded_edges); i += 2)
{
- struct redirection_data *rd;
-
- rd = VARRAY_GENERIC_PTR (redirection_data, 0);
-
- 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);
+ edge e = VEC_index (edge, threaded_edges, i);
+ edge e2 = VEC_index (edge, threaded_edges, i + 1);
- 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;
+ e->aux = e2;
+ bitmap_set_bit (threaded_blocks, e->dest->index);
}
-
- /* Done with this block. Clear REDIRECTION_DATA. */
- VARRAY_CLEAR (redirection_data);
}
-/* Walk through all blocks and thread incoming edges to the block's
- destinations as requested. This is the only entry point into this
- file.
-
- Blocks which have one or more incoming edges have INCOMING_EDGE_THREADED
- set in the block's annotation.
- this routine.
-
- 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.
- Returns true if one or more edges were threaded, false otherwise. */
+ Returns true if one or more edges were threaded, false otherwise. */
bool
thread_through_all_blocks (void)
{
- basic_block bb;
bool retval = false;
+ unsigned int i;
+ bitmap_iterator bi;
+ bitmap threaded_blocks;
+
+ 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);
+
+ 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);
}
+
+ if (dump_file && (dump_flags & TDF_STATS))
+ fprintf (dump_file, "\nJumps threaded: %lu\n",
+ thread_stats.num_threaded_edges);
+
+ BITMAP_FREE (threaded_blocks);
+ threaded_blocks = NULL;
+ VEC_free (edge, heap, threaded_edges);
+ threaded_edges = NULL;
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. ie, 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);
+}
OSDN Git Service
