825 lines
26 KiB
C
825 lines
26 KiB
C
/* Thread edges through blocks and update the control flow and SSA graphs.
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Copyright (C) 2004, 2005 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to
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the Free Software Foundation, 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "tree.h"
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#include "flags.h"
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#include "rtl.h"
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#include "tm_p.h"
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#include "ggc.h"
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#include "basic-block.h"
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#include "output.h"
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#include "errors.h"
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#include "expr.h"
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#include "function.h"
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#include "diagnostic.h"
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#include "tree-flow.h"
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#include "tree-dump.h"
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#include "tree-pass.h"
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#include "cfgloop.h"
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/* Given a block B, update the CFG and SSA graph to reflect redirecting
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one or more in-edges to B to instead reach the destination of an
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out-edge from B while preserving any side effects in B.
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i.e., given A->B and B->C, change A->B to be A->C yet still preserve the
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side effects of executing B.
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1. Make a copy of B (including its outgoing edges and statements). Call
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the copy B'. Note B' has no incoming edges or PHIs at this time.
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2. Remove the control statement at the end of B' and all outgoing edges
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except B'->C.
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3. Add a new argument to each PHI in C with the same value as the existing
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argument associated with edge B->C. Associate the new PHI arguments
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with the edge B'->C.
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4. For each PHI in B, find or create a PHI in B' with an identical
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PHI_RESULT. Add an argument to the PHI in B' which has the same
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value as the PHI in B associated with the edge A->B. Associate
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the new argument in the PHI in B' with the edge A->B.
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5. Change the edge A->B to A->B'.
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5a. This automatically deletes any PHI arguments associated with the
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edge A->B in B.
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5b. This automatically associates each new argument added in step 4
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with the edge A->B'.
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6. Repeat for other incoming edges into B.
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7. Put the duplicated resources in B and all the B' blocks into SSA form.
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Note that block duplication can be minimized by first collecting the
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the set of unique destination blocks that the incoming edges should
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be threaded to. Block duplication can be further minimized by using
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B instead of creating B' for one destination if all edges into B are
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going to be threaded to a successor of B.
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We further reduce the number of edges and statements we create by
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not copying all the outgoing edges and the control statement in
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step #1. We instead create a template block without the outgoing
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edges and duplicate the template. */
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/* Steps #5 and #6 of the above algorithm are best implemented by walking
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all the incoming edges which thread to the same destination edge at
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the same time. That avoids lots of table lookups to get information
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for the destination edge.
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To realize that implementation we create a list of incoming edges
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which thread to the same outgoing edge. Thus to implement steps
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#5 and #6 we traverse our hash table of outgoing edge information.
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For each entry we walk the list of incoming edges which thread to
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the current outgoing edge. */
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struct el
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{
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edge e;
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struct el *next;
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};
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/* Main data structure recording information regarding B's duplicate
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blocks. */
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/* We need to efficiently record the unique thread destinations of this
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block and specific information associated with those destinations. We
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may have many incoming edges threaded to the same outgoing edge. This
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can be naturally implemented with a hash table. */
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struct redirection_data
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{
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/* A duplicate of B with the trailing control statement removed and which
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targets a single successor of B. */
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basic_block dup_block;
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/* An outgoing edge from B. DUP_BLOCK will have OUTGOING_EDGE->dest as
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its single successor. */
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edge outgoing_edge;
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/* A list of incoming edges which we want to thread to
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OUTGOING_EDGE->dest. */
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struct el *incoming_edges;
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/* Flag indicating whether or not we should create a duplicate block
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for this thread destination. This is only true if we are threading
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all incoming edges and thus are using BB itself as a duplicate block. */
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bool do_not_duplicate;
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};
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/* Main data structure to hold information for duplicates of BB. */
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static htab_t redirection_data;
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bool rediscover_loops_after_threading;
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/* Data structure of information to pass to hash table traversal routines. */
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struct local_info
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{
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/* The current block we are working on. */
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basic_block bb;
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/* A template copy of BB with no outgoing edges or control statement that
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we use for creating copies. */
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basic_block template_block;
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/* TRUE if we thread one or more jumps, FALSE otherwise. */
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bool jumps_threaded;
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};
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/* Remove the last statement in block BB if it is a control statement
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Also remove all outgoing edges except the edge which reaches DEST_BB.
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If DEST_BB is NULL, then remove all outgoing edges. */
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static void
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remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb)
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{
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block_stmt_iterator bsi;
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edge e;
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edge_iterator ei;
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bsi = bsi_last (bb);
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/* If the duplicate ends with a control statement, then remove it.
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Note that if we are duplicating the template block rather than the
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original basic block, then the duplicate might not have any real
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statements in it. */
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if (!bsi_end_p (bsi)
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&& bsi_stmt (bsi)
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&& (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
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|| TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
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|| TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR))
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bsi_remove (&bsi);
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for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
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{
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if (e->dest != dest_bb)
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remove_edge (e);
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else
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ei_next (&ei);
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}
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}
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/* Create a duplicate of BB which only reaches the destination of the edge
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stored in RD. Record the duplicate block in RD. */
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static void
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create_block_for_threading (basic_block bb, struct redirection_data *rd)
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{
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/* We can use the generic block duplication code and simply remove
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the stuff we do not need. */
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rd->dup_block = duplicate_block (bb, NULL);
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/* Zero out the profile, since the block is unreachable for now. */
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rd->dup_block->frequency = 0;
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rd->dup_block->count = 0;
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/* The call to duplicate_block will copy everything, including the
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useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove
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the useless COND_EXPR or SWITCH_EXPR here rather than having a
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specialized block copier. We also remove all outgoing edges
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from the duplicate block. The appropriate edge will be created
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later. */
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remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL);
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}
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/* Hashing and equality routines for our hash table. */
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static hashval_t
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redirection_data_hash (const void *p)
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{
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edge e = ((struct redirection_data *)p)->outgoing_edge;
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return e->dest->index;
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}
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static int
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redirection_data_eq (const void *p1, const void *p2)
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{
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edge e1 = ((struct redirection_data *)p1)->outgoing_edge;
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edge e2 = ((struct redirection_data *)p2)->outgoing_edge;
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return e1 == e2;
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}
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/* Given an outgoing edge E lookup and return its entry in our hash table.
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If INSERT is true, then we insert the entry into the hash table if
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it is not already present. INCOMING_EDGE is added to the list of incoming
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edges associated with E in the hash table. */
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static struct redirection_data *
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lookup_redirection_data (edge e, edge incoming_edge, enum insert_option insert)
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{
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void **slot;
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struct redirection_data *elt;
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/* Build a hash table element so we can see if E is already
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in the table. */
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elt = xmalloc (sizeof (struct redirection_data));
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elt->outgoing_edge = e;
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elt->dup_block = NULL;
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elt->do_not_duplicate = false;
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elt->incoming_edges = NULL;
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slot = htab_find_slot (redirection_data, elt, insert);
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/* This will only happen if INSERT is false and the entry is not
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in the hash table. */
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if (slot == NULL)
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{
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free (elt);
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return NULL;
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}
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/* This will only happen if E was not in the hash table and
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INSERT is true. */
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if (*slot == NULL)
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{
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*slot = (void *)elt;
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elt->incoming_edges = xmalloc (sizeof (struct el));
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elt->incoming_edges->e = incoming_edge;
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elt->incoming_edges->next = NULL;
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return elt;
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}
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/* E was in the hash table. */
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else
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{
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/* Free ELT as we do not need it anymore, we will extract the
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relevant entry from the hash table itself. */
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free (elt);
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/* Get the entry stored in the hash table. */
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elt = (struct redirection_data *) *slot;
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/* If insertion was requested, then we need to add INCOMING_EDGE
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to the list of incoming edges associated with E. */
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if (insert)
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{
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struct el *el = xmalloc (sizeof (struct el));
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el->next = elt->incoming_edges;
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el->e = incoming_edge;
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elt->incoming_edges = el;
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}
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return elt;
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}
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}
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/* Given a duplicate block and its single destination (both stored
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in RD). Create an edge between the duplicate and its single
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destination.
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Add an additional argument to any PHI nodes at the single
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destination. */
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static void
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create_edge_and_update_destination_phis (struct redirection_data *rd)
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{
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edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU);
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tree phi;
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/* If there are any PHI nodes at the destination of the outgoing edge
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from the duplicate block, then we will need to add a new argument
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to them. The argument should have the same value as the argument
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associated with the outgoing edge stored in RD. */
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for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
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{
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int indx = rd->outgoing_edge->dest_idx;
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add_phi_arg (phi, PHI_ARG_DEF (phi, indx), e);
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}
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}
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/* Hash table traversal callback routine to create duplicate blocks. */
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static int
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create_duplicates (void **slot, void *data)
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{
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struct redirection_data *rd = (struct redirection_data *) *slot;
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struct local_info *local_info = (struct local_info *)data;
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/* If this entry should not have a duplicate created, then there's
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nothing to do. */
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if (rd->do_not_duplicate)
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return 1;
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/* Create a template block if we have not done so already. Otherwise
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use the template to create a new block. */
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if (local_info->template_block == NULL)
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{
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create_block_for_threading (local_info->bb, rd);
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local_info->template_block = rd->dup_block;
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/* We do not create any outgoing edges for the template. We will
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take care of that in a later traversal. That way we do not
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create edges that are going to just be deleted. */
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}
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else
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{
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create_block_for_threading (local_info->template_block, rd);
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/* Go ahead and wire up outgoing edges and update PHIs for the duplicate
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block. */
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create_edge_and_update_destination_phis (rd);
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}
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/* Keep walking the hash table. */
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return 1;
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}
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/* We did not create any outgoing edges for the template block during
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block creation. This hash table traversal callback creates the
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outgoing edge for the template block. */
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static int
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fixup_template_block (void **slot, void *data)
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{
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struct redirection_data *rd = (struct redirection_data *) *slot;
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struct local_info *local_info = (struct local_info *)data;
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/* If this is the template block, then create its outgoing edges
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and halt the hash table traversal. */
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if (rd->dup_block && rd->dup_block == local_info->template_block)
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{
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create_edge_and_update_destination_phis (rd);
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return 0;
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}
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return 1;
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}
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/* Not all jump threading requests are useful. In particular some
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jump threading requests can create irreducible regions which are
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undesirable.
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This routine will examine the BB's incoming edges for jump threading
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requests which, if acted upon, would create irreducible regions. Any
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such jump threading requests found will be pruned away. */
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static void
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prune_undesirable_thread_requests (basic_block bb)
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{
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edge e;
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edge_iterator ei;
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bool may_create_irreducible_region = false;
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unsigned int num_outgoing_edges_into_loop = 0;
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/* For the heuristics below, we need to know if BB has more than
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one outgoing edge into a loop. */
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FOR_EACH_EDGE (e, ei, bb->succs)
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num_outgoing_edges_into_loop += ((e->flags & EDGE_LOOP_EXIT) == 0);
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if (num_outgoing_edges_into_loop > 1)
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{
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edge backedge = NULL;
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/* Consider the effect of threading the edge (0, 1) to 2 on the left
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CFG to produce the right CFG:
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0 0
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1<--+ 2<--------+
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/ \ | | |
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2 3 | 4<----+ |
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\ / | / \ | |
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4---+ E 1-- | --+
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E 3---+
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Threading the (0, 1) edge to 2 effectively creates two loops
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(2, 4, 1) and (4, 1, 3) which are neither disjoint nor nested.
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This is not good.
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However, we do need to be able to thread (0, 1) to 2 or 3
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in the left CFG below (which creates the middle and right
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CFGs with nested loops).
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0 0 0
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1<--+ 2<----+ 3<-+<-+
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/| | | | | | |
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2 | | 3<-+ | 1--+ |
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\| | | | | | |
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3---+ 1--+--+ 2-----+
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A safe heuristic appears to be to only allow threading if BB
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has a single incoming backedge from one of its direct successors. */
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FOR_EACH_EDGE (e, ei, bb->preds)
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{
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if (e->flags & EDGE_DFS_BACK)
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{
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if (backedge)
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{
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backedge = NULL;
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break;
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}
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else
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{
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backedge = e;
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}
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}
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}
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if (backedge && find_edge (bb, backedge->src))
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;
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else
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may_create_irreducible_region = true;
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}
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else
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{
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edge dest = NULL;
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/* If we thread across the loop entry block (BB) into the
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loop and BB is still reached from outside the loop, then
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we would create an irreducible CFG. Consider the effect
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of threading the edge (1, 4) to 5 on the left CFG to produce
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the right CFG
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0 0
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/ \ / \
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1 2 1 2
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\ / | |
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4<----+ 5<->4
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/ \ | |
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E 5---+ E
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Threading the (1, 4) edge to 5 creates two entry points
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into the loop (4, 5) (one from block 1, the other from
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block 2). A classic irreducible region.
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So look at all of BB's incoming edges which are not
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backedges and which are not threaded to the loop exit.
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If that subset of incoming edges do not all thread
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to the same block, then threading any of them will create
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an irreducible region. */
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FOR_EACH_EDGE (e, ei, bb->preds)
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{
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edge e2;
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/* We ignore back edges for now. This may need refinement
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as threading a backedge creates an inner loop which
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we would need to verify has a single entry point.
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If all backedges thread to new locations, then this
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block will no longer have incoming backedges and we
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need not worry about creating irreducible regions
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by threading through BB. I don't think this happens
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enough in practice to worry about it. */
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if (e->flags & EDGE_DFS_BACK)
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continue;
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/* If the incoming edge threads to the loop exit, then it
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is clearly safe. */
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e2 = e->aux;
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if (e2 && (e2->flags & EDGE_LOOP_EXIT))
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continue;
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/* E enters the loop header and is not threaded. We can
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not allow any other incoming edges to thread into
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the loop as that would create an irreducible region. */
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if (!e2)
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{
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may_create_irreducible_region = true;
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break;
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}
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/* We know that this incoming edge threads to a block inside
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the loop. This edge must thread to the same target in
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the loop as any previously seen threaded edges. Otherwise
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we will create an irreducible region. */
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if (!dest)
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dest = e2;
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else if (e2 != dest)
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{
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may_create_irreducible_region = true;
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break;
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}
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}
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}
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/* If we might create an irreducible region, then cancel any of
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the jump threading requests for incoming edges which are
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not backedges and which do not thread to the exit block. */
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if (may_create_irreducible_region)
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{
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FOR_EACH_EDGE (e, ei, bb->preds)
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{
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edge e2;
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/* Ignore back edges. */
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if (e->flags & EDGE_DFS_BACK)
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continue;
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e2 = e->aux;
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/* 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;
|
|
|
|
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);
|
|
|
|
/* 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;
|
|
}
|
|
|
|
/* 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
|
|
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 key to keeping the SSA graph update manageable is to duplicate
|
|
the side effects occurring in BB so that those side effects still
|
|
occur on the paths which bypass BB after redirecting edges.
|
|
|
|
We accomplish this by creating duplicates of BB and arranging for
|
|
the duplicates to unconditionally pass control to one specific
|
|
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 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
|
|
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 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;
|
|
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;
|
|
|
|
/* 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);
|
|
|
|
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)
|
|
{
|
|
all = false;
|
|
}
|
|
else
|
|
{
|
|
edge e2 = e->aux;
|
|
|
|
/* If we thread to a loop exit edge, then we will need to
|
|
rediscover the loop exit edges. While it may seem that
|
|
the new edge is a loop exit edge, that is not the case.
|
|
Consider threading the edge (5,6) to E in the CFG on the
|
|
left which creates the CFG on the right:
|
|
|
|
|
|
0<--+ 0<---+
|
|
/ \ | / \ |
|
|
1 2 | 1 2 |
|
|
/ \ | | / \ | |
|
|
3 4 | | 3 4 6--+
|
|
\ / | | \ /
|
|
5 | | 5
|
|
\ / | |
|
|
6---+ E
|
|
|
|
|
E
|
|
|
|
After threading, the edge (0, 1) is the loop exit edge and
|
|
the nodes 0, 2, 6 are the only nodes in the loop. */
|
|
if (e2->flags & EDGE_LOOP_EXIT)
|
|
rediscover_loops_after_threading = true;
|
|
|
|
/* Insert the outgoing edge into the hash table if it is not
|
|
already in the hash table. */
|
|
lookup_redirection_data (e2, e, INSERT);
|
|
}
|
|
}
|
|
|
|
/* 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.
|
|
|
|
So we first duplicate BB and remove the control structure at the
|
|
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. */
|
|
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
|
|
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;
|
|
}
|
|
|
|
/* 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.
|
|
|
|
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.
|
|
|
|
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. */
|
|
|
|
bool
|
|
thread_through_all_blocks (void)
|
|
{
|
|
basic_block bb;
|
|
bool retval = false;
|
|
|
|
rediscover_loops_after_threading = false;
|
|
|
|
FOR_EACH_BB (bb)
|
|
{
|
|
if (bb_ann (bb)->incoming_edge_threaded
|
|
&& EDGE_COUNT (bb->preds) > 0)
|
|
{
|
|
retval |= thread_block (bb);
|
|
bb_ann (bb)->incoming_edge_threaded = false;
|
|
|
|
}
|
|
}
|
|
|
|
return retval;
|
|
}
|