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author | Dan Albert <danalbert@google.com> | 2016-02-24 13:48:45 -0800 |
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committer | Dan Albert <danalbert@google.com> | 2016-02-24 13:51:18 -0800 |
commit | b9de1157289455b0ca26daff519d4a0ddcd1fa13 (patch) | |
tree | 4c56cc0a34b91f17033a40a455f26652304f7b8d /gcc-4.8.3/gcc/tree-ssa-threadupdate.c | |
parent | 098157a754787181cfa10e71325832448ddcea98 (diff) | |
download | toolchain_gcc-b9de1157289455b0ca26daff519d4a0ddcd1fa13.tar.gz toolchain_gcc-b9de1157289455b0ca26daff519d4a0ddcd1fa13.tar.bz2 toolchain_gcc-b9de1157289455b0ca26daff519d4a0ddcd1fa13.zip |
Update 4.8.1 to 4.8.3.
My previous drop was the wrong version. The platform mingw is
currently using 4.8.3, not 4.8.1 (not sure how I got that wrong).
From ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.3/gcc-4.8.3.tar.bz2.
Bug: http://b/26523949
Change-Id: Id85f1bdcbbaf78c7d0b5a69e74c798a08f341c35
Diffstat (limited to 'gcc-4.8.3/gcc/tree-ssa-threadupdate.c')
-rw-r--r-- | gcc-4.8.3/gcc/tree-ssa-threadupdate.c | 1285 |
1 files changed, 1285 insertions, 0 deletions
diff --git a/gcc-4.8.3/gcc/tree-ssa-threadupdate.c b/gcc-4.8.3/gcc/tree-ssa-threadupdate.c new file mode 100644 index 000000000..0e4cbc98c --- /dev/null +++ b/gcc-4.8.3/gcc/tree-ssa-threadupdate.c @@ -0,0 +1,1285 @@ +/* Thread edges through blocks and update the control flow and SSA graphs. + Copyright (C) 2004-2013 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 3, or (at your option) +any later version. + +GCC is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +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 COPYING3. If not see +<http://www.gnu.org/licenses/>. */ + +#include "config.h" +#include "system.h" +#include "coretypes.h" +#include "tm.h" +#include "tree.h" +#include "flags.h" +#include "tm_p.h" +#include "basic-block.h" +#include "function.h" +#include "tree-flow.h" +#include "dumpfile.h" +#include "cfgloop.h" +#include "hash-table.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 + out-edge from B while preserving any side effects in B. + + i.e., given A->B and B->C, change A->B to be A->C yet still preserve the + side effects of executing B. + + 1. Make a copy of B (including its outgoing edges and statements). Call + the copy B'. Note B' has no incoming edges or PHIs at this time. + + 2. Remove the control statement at the end of B' and all outgoing edges + except B'->C. + + 3. Add a new argument to each PHI in C with the same value as the existing + argument associated with edge B->C. Associate the new PHI arguments + with the edge B'->C. + + 4. For each PHI in B, find or create a PHI in B' with an identical + PHI_RESULT. Add an argument to the PHI in B' which has the same + value as the PHI in B associated with the edge A->B. Associate + the new argument in the PHI in B' with the edge A->B. + + 5. Change the edge A->B to A->B'. + + 5a. This automatically deletes any PHI arguments associated with the + edge A->B in B. + + 5b. This automatically associates each new argument added in step 4 + with the edge A->B'. + + 6. Repeat for other incoming edges into B. + + 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 + 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 + 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 : typed_free_remove<redirection_data> +{ + /* A duplicate of B with the trailing control statement removed and which + targets a single successor of B. */ + basic_block dup_block; + + /* An outgoing edge from B. DUP_BLOCK will have OUTGOING_EDGE->dest as + 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; + + /* hash_table support. */ + typedef redirection_data value_type; + typedef redirection_data compare_type; + static inline hashval_t hash (const value_type *); + static inline int equal (const value_type *, const compare_type *); +}; + +inline hashval_t +redirection_data::hash (const value_type *p) +{ + edge e = p->outgoing_edge; + return e->dest->index; +} + +inline int +redirection_data::equal (const value_type *p1, const compare_type *p2) +{ + edge e1 = p1->outgoing_edge; + edge e2 = p2->outgoing_edge; + edge e3 = p1->intermediate_edge; + edge e4 = p2->intermediate_edge; + return e1 == e2 && e3 == e4; +} + +/* Data structure of information to pass to hash table traversal routines. */ +struct ssa_local_info_t +{ + /* The current block we are working on. */ + basic_block bb; + + /* A template copy of BB with no outgoing edges or control statement that + we use for creating copies. */ + basic_block template_block; + + /* TRUE if we thread one or more jumps, FALSE otherwise. */ + bool jumps_threaded; +}; + +/* Passes which use the jump threading code register jump threading + opportunities as they are discovered. We keep the registered + jump threading opportunities in this vector as edge pairs + (original_edge, target_edge). */ +static vec<edge> 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) +{ + gimple_stmt_iterator gsi; + edge e; + edge_iterator ei; + + 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 (!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) + remove_edge (e); + else + ei_next (&ei); + } +} + +/* 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, 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; +} + +/* Main data structure to hold information for duplicates of BB. */ + +static hash_table <redirection_data> redirection_data; + +/* 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, enum insert_option insert) +{ + struct redirection_data **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->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->incoming_edges = NULL; + + slot = redirection_data.find_slot (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 = elt; + elt->incoming_edges = XNEW (struct el); + elt->incoming_edges->e = e; + 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 = *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 = e; + elt->incoming_edges = el; + } + + return elt; + } +} + +/* 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. + + Add an additional argument to any PHI nodes at the single + destination. */ + +static void +create_edge_and_update_destination_phis (struct redirection_data *rd, + basic_block bb) +{ + 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 = 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. */ + copy_phi_args (e->dest, rd->outgoing_edge, e); +} + +/* Wire up the outgoing edges from the duplicate block and + update any PHIs as needed. */ +void +ssa_fix_duplicate_block_edges (struct redirection_data *rd, + ssa_local_info_t *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 + { + 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. */ + +int +ssa_create_duplicates (struct redirection_data **slot, + ssa_local_info_t *local_info) +{ + struct redirection_data *rd = *slot; + + /* 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. */ + ssa_fix_duplicate_block_edges (rd, local_info); + } + + /* 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. */ + +inline int +ssa_fixup_template_block (struct redirection_data **slot, + ssa_local_info_t *local_info) +{ + struct redirection_data *rd = *slot; + + /* 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) + { + ssa_fix_duplicate_block_edges (rd, local_info); + return 0; + } + + return 1; +} + +/* Hash table traversal callback to redirect each incoming edge + associated with this hash table element to its new destination. */ + +int +ssa_redirect_edges (struct redirection_data **slot, + ssa_local_info_t *local_info) +{ + struct redirection_data *rd = *slot; + 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); + + 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; + + /* 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; + + 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; + + /* 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); + } + + /* 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; + + } + + /* Indicate that we actually threaded one or more jumps. */ + if (rd->incoming_edges) + local_info->jumps_threaded = true; + + return 1; +} + +/* Return true if this block has no executable statements other than + a simple ctrl flow instruction. When the number of outgoing edges + is one, this is equivalent to a "forwarder" block. */ + +static bool +redirection_block_p (basic_block bb) +{ + gimple_stmt_iterator gsi; + + /* Advance to the first executable statement. */ + gsi = gsi_start_bb (bb); + while (!gsi_end_p (gsi) + && (gimple_code (gsi_stmt (gsi)) == GIMPLE_LABEL + || is_gimple_debug (gsi_stmt (gsi)) + || gimple_nop_p (gsi_stmt (gsi)))) + gsi_next (&gsi); + + /* Check if this is an empty block. */ + if (gsi_end_p (gsi)) + return true; + + /* Test that we've reached the terminating control statement. */ + return gsi_stmt (gsi) + && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND + || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO + || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH); +} + +/* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB + is reached via one or more specific incoming edges, we know which + outgoing edge from BB will be traversed. + + We want to redirect those incoming edges to the target of the + 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. + + 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. */ + +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, e2; + edge_iterator ei; + ssa_local_info_t local_info; + 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 + difference. However, if we have a block with a large number of + incoming and outgoing edges such linear searches can get expensive. */ + redirection_data.create (EDGE_COUNT (bb->succs)); + + /* If we thread the latch of the loop to its exit, the loop ceases to + exist. Make sure we do not restrict ourselves in order to preserve + this loop. */ + if (loop->header == bb) + { + e = loop_latch_edge (loop); + + if (e->aux) + e2 = THREAD_TARGET (e); + else + e2 = NULL; + + if (e2 && loop_exit_edge_p (loop, e2)) + { + loop->header = NULL; + loop->latch = NULL; + loops_state_set (LOOPS_NEED_FIXUP); + } + } + + /* Record each unique threaded destination into a hash table for + efficient lookups. */ + FOR_EACH_EDGE (e, ei, bb->preds) + { + 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); + + /* We know we only thread through the loop header to loop exits. + Let the basic block duplication hook know we are not creating + a multiple entry loop. */ + if (noloop_only + && bb == bb->loop_father->header) + set_loop_copy (bb->loop_father, loop_outer (bb->loop_father)); + + /* 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; + redirection_data.traverse <ssa_local_info_t *, ssa_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. */ + redirection_data.traverse <ssa_local_info_t *, ssa_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. */ + redirection_data.traverse <ssa_local_info_t *, ssa_redirect_edges> + (&local_info); + + /* Done with this block. Clear REDIRECTION_DATA. */ + redirection_data.dispose (); + + if (noloop_only + && bb == bb->loop_father->header) + set_loop_copy (bb->loop_father, 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); +} + +/* 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; + } + + 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); +} + +/* Return true if BB is part of the new pre-header that is created + when threading the latch to DATA. */ + +static bool +def_split_header_continue_p (const_basic_block bb, const void *data) +{ + const_basic_block new_header = (const_basic_block) data; + const struct loop *l; + + if (bb == new_header + || loop_depth (bb->loop_father) < loop_depth (new_header->loop_father)) + return false; + for (l = bb->loop_father; l; l = loop_outer (l)) + if (l == new_header->loop_father) + return true; + return false; +} + +/* Thread jumps through the header of LOOP. Returns true if cfg changes. + If MAY_PEEL_LOOP_HEADERS is false, we avoid threading from entry edges + to the inside of the loop. */ + +static bool +thread_through_loop_header (struct loop *loop, bool may_peel_loop_headers) +{ + basic_block header = loop->header; + edge e, tgt_edge, latch = loop_latch_edge (loop); + edge_iterator ei; + basic_block tgt_bb, atgt_bb; + enum bb_dom_status domst; + + /* We have already threaded through headers to exits, so all the threading + requests now are to the inside of the loop. We need to avoid creating + irreducible regions (i.e., loops with more than one entry block), and + also loop with several latch edges, or new subloops of the loop (although + there are cases where it might be appropriate, it is difficult to decide, + and doing it wrongly may confuse other optimizers). + + We could handle more general cases here. However, the intention is to + preserve some information about the loop, which is impossible if its + structure changes significantly, in a way that is not well understood. + Thus we only handle few important special cases, in which also updating + of the loop-carried information should be feasible: + + 1) Propagation of latch edge to a block that dominates the latch block + of a loop. This aims to handle the following idiom: + + first = 1; + while (1) + { + if (first) + initialize; + first = 0; + body; + } + + After threading the latch edge, this becomes + + first = 1; + if (first) + initialize; + while (1) + { + first = 0; + body; + } + + The original header of the loop is moved out of it, and we may thread + the remaining edges through it without further constraints. + + 2) All entry edges are propagated to a single basic block that dominates + the latch block of the loop. This aims to handle the following idiom + (normally created for "for" loops): + + i = 0; + while (1) + { + if (i >= 100) + break; + body; + i++; + } + + This becomes + + i = 0; + while (1) + { + body; + i++; + if (i >= 100) + break; + } + */ + + /* 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; + loops_state_set (LOOPS_NEED_FIXUP); + 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) + { + basic_block *bblocks; + unsigned nblocks, i; + + /* First handle the case latch edge is redirected. We are copying + the loop header but not creating a multiple entry loop. Make the + cfg manipulation code aware of that fact. */ + set_loop_copy (loop, loop); + loop->latch = thread_single_edge (latch); + set_loop_copy (loop, NULL); + gcc_assert (single_succ (loop->latch) == tgt_bb); + loop->header = tgt_bb; + + /* Remove the new pre-header blocks from our loop. */ + bblocks = XCNEWVEC (basic_block, loop->num_nodes); + nblocks = dfs_enumerate_from (header, 0, def_split_header_continue_p, + bblocks, loop->num_nodes, tgt_bb); + for (i = 0; i < nblocks; i++) + if (bblocks[i]->loop_father == loop) + { + remove_bb_from_loops (bblocks[i]); + add_bb_to_loop (bblocks[i], loop_outer (loop)); + } + free (bblocks); + + /* If the new header has multiple latches mark it so. */ + FOR_EACH_EDGE (e, ei, loop->header->preds) + if (e->src->loop_father == loop + && e->src != loop->latch) + { + loop->latch = NULL; + loops_state_set (LOOPS_MAY_HAVE_MULTIPLE_LATCHES); + } + + /* Cancel remaining threading requests that would make the + loop a multiple entry loop. */ + FOR_EACH_EDGE (e, ei, header->preds) + { + edge e2; + + if (e->aux == NULL) + continue; + + if (THREAD_TARGET2 (e)) + e2 = THREAD_TARGET2 (e); + else + e2 = THREAD_TARGET (e); + + if (e->src->loop_father != e2->dest->loop_father + && e2->dest != loop->header) + { + free (e->aux); + e->aux = NULL; + } + } + + /* 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 < threaded_edges.length (); i += 3) + { + edge e = threaded_edges[i]; + edge *x = XNEWVEC (edge, 2); + + e->aux = x; + THREAD_TARGET (e) = threaded_edges[i + 1]; + THREAD_TARGET2 (e) = 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 (bool may_peel_loop_headers) +{ + 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.exists ()) + return false; + + 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) + { + 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; + threaded_edges.release (); + + 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.exists ()) + threaded_edges.create (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"); + + threaded_edges.safe_push (e); + threaded_edges.safe_push (e2); + threaded_edges.safe_push (e3); +} |