chromium / native_client / nacl-gcc / f80d6b9ee7f94755c697ffb7194fb01dd0c537dd / . / gcc / cfganal.c

/* Control flow graph analysis code for GNU compiler. | |

Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998, | |

1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007, 2008 | |

Free Software Foundation, Inc. | |

This file is part of GCC. | |

GCC is free software; you can redistribute it and/or modify it under | |

the terms of the GNU General Public License as published by the Free | |

Software Foundation; either version 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/>. */ | |

/* This file contains various simple utilities to analyze the CFG. */ | |

#include "config.h" | |

#include "system.h" | |

#include "coretypes.h" | |

#include "tm.h" | |

#include "rtl.h" | |

#include "obstack.h" | |

#include "hard-reg-set.h" | |

#include "basic-block.h" | |

#include "insn-config.h" | |

#include "recog.h" | |

#include "toplev.h" | |

#include "tm_p.h" | |

#include "vec.h" | |

#include "vecprim.h" | |

#include "timevar.h" | |

/* Store the data structures necessary for depth-first search. */ | |

struct depth_first_search_dsS { | |

/* stack for backtracking during the algorithm */ | |

basic_block *stack; | |

/* number of edges in the stack. That is, positions 0, ..., sp-1 | |

have edges. */ | |

unsigned int sp; | |

/* record of basic blocks already seen by depth-first search */ | |

sbitmap visited_blocks; | |

}; | |

typedef struct depth_first_search_dsS *depth_first_search_ds; | |

static void flow_dfs_compute_reverse_init (depth_first_search_ds); | |

static void flow_dfs_compute_reverse_add_bb (depth_first_search_ds, | |

basic_block); | |

static basic_block flow_dfs_compute_reverse_execute (depth_first_search_ds, | |

basic_block); | |

static void flow_dfs_compute_reverse_finish (depth_first_search_ds); | |

static bool flow_active_insn_p (const_rtx); | |

/* Like active_insn_p, except keep the return value clobber around | |

even after reload. */ | |

static bool | |

flow_active_insn_p (const_rtx insn) | |

{ | |

if (active_insn_p (insn)) | |

return true; | |

/* A clobber of the function return value exists for buggy | |

programs that fail to return a value. Its effect is to | |

keep the return value from being live across the entire | |

function. If we allow it to be skipped, we introduce the | |

possibility for register lifetime confusion. */ | |

if (GET_CODE (PATTERN (insn)) == CLOBBER | |

&& REG_P (XEXP (PATTERN (insn), 0)) | |

&& REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0))) | |

return true; | |

return false; | |

} | |

/* Return true if the block has no effect and only forwards control flow to | |

its single destination. */ | |

bool | |

forwarder_block_p (const_basic_block bb) | |

{ | |

rtx insn; | |

if (bb == EXIT_BLOCK_PTR || bb == ENTRY_BLOCK_PTR | |

|| !single_succ_p (bb)) | |

return false; | |

for (insn = BB_HEAD (bb); insn != BB_END (bb); insn = NEXT_INSN (insn)) | |

if (INSN_P (insn) && flow_active_insn_p (insn)) | |

return false; | |

return (!INSN_P (insn) | |

|| (JUMP_P (insn) && simplejump_p (insn)) | |

|| !flow_active_insn_p (insn)); | |

} | |

/* Return nonzero if we can reach target from src by falling through. */ | |

bool | |

can_fallthru (basic_block src, basic_block target) | |

{ | |

rtx insn = BB_END (src); | |

rtx insn2; | |

edge e; | |

edge_iterator ei; | |

if (target == EXIT_BLOCK_PTR) | |

return true; | |

if (src->next_bb != target) | |

return 0; | |

FOR_EACH_EDGE (e, ei, src->succs) | |

if (e->dest == EXIT_BLOCK_PTR | |

&& e->flags & EDGE_FALLTHRU) | |

return 0; | |

insn2 = BB_HEAD (target); | |

if (insn2 && !active_insn_p (insn2)) | |

insn2 = next_active_insn (insn2); | |

/* ??? Later we may add code to move jump tables offline. */ | |

return next_active_insn (insn) == insn2; | |

} | |

/* Return nonzero if we could reach target from src by falling through, | |

if the target was made adjacent. If we already have a fall-through | |

edge to the exit block, we can't do that. */ | |

bool | |

could_fall_through (basic_block src, basic_block target) | |

{ | |

edge e; | |

edge_iterator ei; | |

if (target == EXIT_BLOCK_PTR) | |

return true; | |

FOR_EACH_EDGE (e, ei, src->succs) | |

if (e->dest == EXIT_BLOCK_PTR | |

&& e->flags & EDGE_FALLTHRU) | |

return 0; | |

return true; | |

} | |

/* Mark the back edges in DFS traversal. | |

Return nonzero if a loop (natural or otherwise) is present. | |

Inspired by Depth_First_Search_PP described in: | |

Advanced Compiler Design and Implementation | |

Steven Muchnick | |

Morgan Kaufmann, 1997 | |

and heavily borrowed from pre_and_rev_post_order_compute. */ | |

bool | |

mark_dfs_back_edges (void) | |

{ | |

edge_iterator *stack; | |

int *pre; | |

int *post; | |

int sp; | |

int prenum = 1; | |

int postnum = 1; | |

sbitmap visited; | |

bool found = false; | |

/* Allocate the preorder and postorder number arrays. */ | |

pre = XCNEWVEC (int, last_basic_block); | |

post = XCNEWVEC (int, last_basic_block); | |

/* Allocate stack for back-tracking up CFG. */ | |

stack = XNEWVEC (edge_iterator, n_basic_blocks + 1); | |

sp = 0; | |

/* Allocate bitmap to track nodes that have been visited. */ | |

visited = sbitmap_alloc (last_basic_block); | |

/* None of the nodes in the CFG have been visited yet. */ | |

sbitmap_zero (visited); | |

/* Push the first edge on to the stack. */ | |

stack[sp++] = ei_start (ENTRY_BLOCK_PTR->succs); | |

while (sp) | |

{ | |

edge_iterator ei; | |

basic_block src; | |

basic_block dest; | |

/* Look at the edge on the top of the stack. */ | |

ei = stack[sp - 1]; | |

src = ei_edge (ei)->src; | |

dest = ei_edge (ei)->dest; | |

ei_edge (ei)->flags &= ~EDGE_DFS_BACK; | |

/* Check if the edge destination has been visited yet. */ | |

if (dest != EXIT_BLOCK_PTR && ! TEST_BIT (visited, dest->index)) | |

{ | |

/* Mark that we have visited the destination. */ | |

SET_BIT (visited, dest->index); | |

pre[dest->index] = prenum++; | |

if (EDGE_COUNT (dest->succs) > 0) | |

{ | |

/* Since the DEST node has been visited for the first | |

time, check its successors. */ | |

stack[sp++] = ei_start (dest->succs); | |

} | |

else | |

post[dest->index] = postnum++; | |

} | |

else | |

{ | |

if (dest != EXIT_BLOCK_PTR && src != ENTRY_BLOCK_PTR | |

&& pre[src->index] >= pre[dest->index] | |

&& post[dest->index] == 0) | |

ei_edge (ei)->flags |= EDGE_DFS_BACK, found = true; | |

if (ei_one_before_end_p (ei) && src != ENTRY_BLOCK_PTR) | |

post[src->index] = postnum++; | |

if (!ei_one_before_end_p (ei)) | |

ei_next (&stack[sp - 1]); | |

else | |

sp--; | |

} | |

} | |

free (pre); | |

free (post); | |

free (stack); | |

sbitmap_free (visited); | |

return found; | |

} | |

/* Set the flag EDGE_CAN_FALLTHRU for edges that can be fallthru. */ | |

void | |

set_edge_can_fallthru_flag (void) | |

{ | |

basic_block bb; | |

FOR_EACH_BB (bb) | |

{ | |

edge e; | |

edge_iterator ei; | |

FOR_EACH_EDGE (e, ei, bb->succs) | |

{ | |

e->flags &= ~EDGE_CAN_FALLTHRU; | |

/* The FALLTHRU edge is also CAN_FALLTHRU edge. */ | |

if (e->flags & EDGE_FALLTHRU) | |

e->flags |= EDGE_CAN_FALLTHRU; | |

} | |

/* If the BB ends with an invertible condjump all (2) edges are | |

CAN_FALLTHRU edges. */ | |

if (EDGE_COUNT (bb->succs) != 2) | |

continue; | |

if (!any_condjump_p (BB_END (bb))) | |

continue; | |

if (!invert_jump (BB_END (bb), JUMP_LABEL (BB_END (bb)), 0)) | |

continue; | |

invert_jump (BB_END (bb), JUMP_LABEL (BB_END (bb)), 0); | |

EDGE_SUCC (bb, 0)->flags |= EDGE_CAN_FALLTHRU; | |

EDGE_SUCC (bb, 1)->flags |= EDGE_CAN_FALLTHRU; | |

} | |

} | |

/* Find unreachable blocks. An unreachable block will have 0 in | |

the reachable bit in block->flags. A nonzero value indicates the | |

block is reachable. */ | |

void | |

find_unreachable_blocks (void) | |

{ | |

edge e; | |

edge_iterator ei; | |

basic_block *tos, *worklist, bb; | |

tos = worklist = XNEWVEC (basic_block, n_basic_blocks); | |

/* Clear all the reachability flags. */ | |

FOR_EACH_BB (bb) | |

bb->flags &= ~BB_REACHABLE; | |

/* Add our starting points to the worklist. Almost always there will | |

be only one. It isn't inconceivable that we might one day directly | |

support Fortran alternate entry points. */ | |

FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR->succs) | |

{ | |

*tos++ = e->dest; | |

/* Mark the block reachable. */ | |

e->dest->flags |= BB_REACHABLE; | |

} | |

/* Iterate: find everything reachable from what we've already seen. */ | |

while (tos != worklist) | |

{ | |

basic_block b = *--tos; | |

FOR_EACH_EDGE (e, ei, b->succs) | |

{ | |

basic_block dest = e->dest; | |

if (!(dest->flags & BB_REACHABLE)) | |

{ | |

*tos++ = dest; | |

dest->flags |= BB_REACHABLE; | |

} | |

} | |

} | |

free (worklist); | |

} | |

/* Functions to access an edge list with a vector representation. | |

Enough data is kept such that given an index number, the | |

pred and succ that edge represents can be determined, or | |

given a pred and a succ, its index number can be returned. | |

This allows algorithms which consume a lot of memory to | |

represent the normally full matrix of edge (pred,succ) with a | |

single indexed vector, edge (EDGE_INDEX (pred, succ)), with no | |

wasted space in the client code due to sparse flow graphs. */ | |

/* This functions initializes the edge list. Basically the entire | |

flowgraph is processed, and all edges are assigned a number, | |

and the data structure is filled in. */ | |

struct edge_list * | |

create_edge_list (void) | |

{ | |

struct edge_list *elist; | |

edge e; | |

int num_edges; | |

int block_count; | |

basic_block bb; | |

edge_iterator ei; | |

block_count = n_basic_blocks; /* Include the entry and exit blocks. */ | |

num_edges = 0; | |

/* Determine the number of edges in the flow graph by counting successor | |

edges on each basic block. */ | |

FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb) | |

{ | |

num_edges += EDGE_COUNT (bb->succs); | |

} | |

elist = XNEW (struct edge_list); | |

elist->num_blocks = block_count; | |

elist->num_edges = num_edges; | |

elist->index_to_edge = XNEWVEC (edge, num_edges); | |

num_edges = 0; | |

/* Follow successors of blocks, and register these edges. */ | |

FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb) | |

FOR_EACH_EDGE (e, ei, bb->succs) | |

elist->index_to_edge[num_edges++] = e; | |

return elist; | |

} | |

/* This function free's memory associated with an edge list. */ | |

void | |

free_edge_list (struct edge_list *elist) | |

{ | |

if (elist) | |

{ | |

free (elist->index_to_edge); | |

free (elist); | |

} | |

} | |

/* This function provides debug output showing an edge list. */ | |

void | |

print_edge_list (FILE *f, struct edge_list *elist) | |

{ | |

int x; | |

fprintf (f, "Compressed edge list, %d BBs + entry & exit, and %d edges\n", | |

elist->num_blocks, elist->num_edges); | |

for (x = 0; x < elist->num_edges; x++) | |

{ | |

fprintf (f, " %-4d - edge(", x); | |

if (INDEX_EDGE_PRED_BB (elist, x) == ENTRY_BLOCK_PTR) | |

fprintf (f, "entry,"); | |

else | |

fprintf (f, "%d,", INDEX_EDGE_PRED_BB (elist, x)->index); | |

if (INDEX_EDGE_SUCC_BB (elist, x) == EXIT_BLOCK_PTR) | |

fprintf (f, "exit)\n"); | |

else | |

fprintf (f, "%d)\n", INDEX_EDGE_SUCC_BB (elist, x)->index); | |

} | |

} | |

/* This function provides an internal consistency check of an edge list, | |

verifying that all edges are present, and that there are no | |

extra edges. */ | |

void | |

verify_edge_list (FILE *f, struct edge_list *elist) | |

{ | |

int pred, succ, index; | |

edge e; | |

basic_block bb, p, s; | |

edge_iterator ei; | |

FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb) | |

{ | |

FOR_EACH_EDGE (e, ei, bb->succs) | |

{ | |

pred = e->src->index; | |

succ = e->dest->index; | |

index = EDGE_INDEX (elist, e->src, e->dest); | |

if (index == EDGE_INDEX_NO_EDGE) | |

{ | |

fprintf (f, "*p* No index for edge from %d to %d\n", pred, succ); | |

continue; | |

} | |

if (INDEX_EDGE_PRED_BB (elist, index)->index != pred) | |

fprintf (f, "*p* Pred for index %d should be %d not %d\n", | |

index, pred, INDEX_EDGE_PRED_BB (elist, index)->index); | |

if (INDEX_EDGE_SUCC_BB (elist, index)->index != succ) | |

fprintf (f, "*p* Succ for index %d should be %d not %d\n", | |

index, succ, INDEX_EDGE_SUCC_BB (elist, index)->index); | |

} | |

} | |

/* We've verified that all the edges are in the list, now lets make sure | |

there are no spurious edges in the list. */ | |

FOR_BB_BETWEEN (p, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb) | |

FOR_BB_BETWEEN (s, ENTRY_BLOCK_PTR->next_bb, NULL, next_bb) | |

{ | |

int found_edge = 0; | |

FOR_EACH_EDGE (e, ei, p->succs) | |

if (e->dest == s) | |

{ | |

found_edge = 1; | |

break; | |

} | |

FOR_EACH_EDGE (e, ei, s->preds) | |

if (e->src == p) | |

{ | |

found_edge = 1; | |

break; | |

} | |

if (EDGE_INDEX (elist, p, s) | |

== EDGE_INDEX_NO_EDGE && found_edge != 0) | |

fprintf (f, "*** Edge (%d, %d) appears to not have an index\n", | |

p->index, s->index); | |

if (EDGE_INDEX (elist, p, s) | |

!= EDGE_INDEX_NO_EDGE && found_edge == 0) | |

fprintf (f, "*** Edge (%d, %d) has index %d, but there is no edge\n", | |

p->index, s->index, EDGE_INDEX (elist, p, s)); | |

} | |

} | |

/* Given PRED and SUCC blocks, return the edge which connects the blocks. | |

If no such edge exists, return NULL. */ | |

edge | |

find_edge (basic_block pred, basic_block succ) | |

{ | |

edge e; | |

edge_iterator ei; | |

if (EDGE_COUNT (pred->succs) <= EDGE_COUNT (succ->preds)) | |

{ | |

FOR_EACH_EDGE (e, ei, pred->succs) | |

if (e->dest == succ) | |

return e; | |

} | |

else | |

{ | |

FOR_EACH_EDGE (e, ei, succ->preds) | |

if (e->src == pred) | |

return e; | |

} | |

return NULL; | |

} | |

/* This routine will determine what, if any, edge there is between | |

a specified predecessor and successor. */ | |

int | |

find_edge_index (struct edge_list *edge_list, basic_block pred, basic_block succ) | |

{ | |

int x; | |

for (x = 0; x < NUM_EDGES (edge_list); x++) | |

if (INDEX_EDGE_PRED_BB (edge_list, x) == pred | |

&& INDEX_EDGE_SUCC_BB (edge_list, x) == succ) | |

return x; | |

return (EDGE_INDEX_NO_EDGE); | |

} | |

/* Dump the list of basic blocks in the bitmap NODES. */ | |

void | |

flow_nodes_print (const char *str, const_sbitmap nodes, FILE *file) | |

{ | |

unsigned int node = 0; | |

sbitmap_iterator sbi; | |

if (! nodes) | |

return; | |

fprintf (file, "%s { ", str); | |

EXECUTE_IF_SET_IN_SBITMAP (nodes, 0, node, sbi) | |

fprintf (file, "%d ", node); | |

fputs ("}\n", file); | |

} | |

/* Dump the list of edges in the array EDGE_LIST. */ | |

void | |

flow_edge_list_print (const char *str, const edge *edge_list, int num_edges, FILE *file) | |

{ | |

int i; | |

if (! edge_list) | |

return; | |

fprintf (file, "%s { ", str); | |

for (i = 0; i < num_edges; i++) | |

fprintf (file, "%d->%d ", edge_list[i]->src->index, | |

edge_list[i]->dest->index); | |

fputs ("}\n", file); | |

} | |

/* This routine will remove any fake predecessor edges for a basic block. | |

When the edge is removed, it is also removed from whatever successor | |

list it is in. */ | |

static void | |

remove_fake_predecessors (basic_block bb) | |

{ | |

edge e; | |

edge_iterator ei; | |

for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); ) | |

{ | |

if ((e->flags & EDGE_FAKE) == EDGE_FAKE) | |

remove_edge (e); | |

else | |

ei_next (&ei); | |

} | |

} | |

/* This routine will remove all fake edges from the flow graph. If | |

we remove all fake successors, it will automatically remove all | |

fake predecessors. */ | |

void | |

remove_fake_edges (void) | |

{ | |

basic_block bb; | |

FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR->next_bb, NULL, next_bb) | |

remove_fake_predecessors (bb); | |

} | |

/* This routine will remove all fake edges to the EXIT_BLOCK. */ | |

void | |

remove_fake_exit_edges (void) | |

{ | |

remove_fake_predecessors (EXIT_BLOCK_PTR); | |

} | |

/* This function will add a fake edge between any block which has no | |

successors, and the exit block. Some data flow equations require these | |

edges to exist. */ | |

void | |

add_noreturn_fake_exit_edges (void) | |

{ | |

basic_block bb; | |

FOR_EACH_BB (bb) | |

if (EDGE_COUNT (bb->succs) == 0) | |

make_single_succ_edge (bb, EXIT_BLOCK_PTR, EDGE_FAKE); | |

} | |

/* This function adds a fake edge between any infinite loops to the | |

exit block. Some optimizations require a path from each node to | |

the exit node. | |

See also Morgan, Figure 3.10, pp. 82-83. | |

The current implementation is ugly, not attempting to minimize the | |

number of inserted fake edges. To reduce the number of fake edges | |

to insert, add fake edges from _innermost_ loops containing only | |

nodes not reachable from the exit block. */ | |

void | |

connect_infinite_loops_to_exit (void) | |

{ | |

basic_block unvisited_block = EXIT_BLOCK_PTR; | |

struct depth_first_search_dsS dfs_ds; | |

/* Perform depth-first search in the reverse graph to find nodes | |

reachable from the exit block. */ | |

flow_dfs_compute_reverse_init (&dfs_ds); | |

flow_dfs_compute_reverse_add_bb (&dfs_ds, EXIT_BLOCK_PTR); | |

/* Repeatedly add fake edges, updating the unreachable nodes. */ | |

while (1) | |

{ | |

unvisited_block = flow_dfs_compute_reverse_execute (&dfs_ds, | |

unvisited_block); | |

if (!unvisited_block) | |

break; | |

make_edge (unvisited_block, EXIT_BLOCK_PTR, EDGE_FAKE); | |

flow_dfs_compute_reverse_add_bb (&dfs_ds, unvisited_block); | |

} | |

flow_dfs_compute_reverse_finish (&dfs_ds); | |

return; | |

} | |

/* Compute reverse top sort order. This is computing a post order | |

numbering of the graph. If INCLUDE_ENTRY_EXIT is true, then then | |

ENTRY_BLOCK and EXIT_BLOCK are included. If DELETE_UNREACHABLE is | |

true, unreachable blocks are deleted. */ | |

int | |

post_order_compute (int *post_order, bool include_entry_exit, | |

bool delete_unreachable) | |

{ | |

edge_iterator *stack; | |

int sp; | |

int post_order_num = 0; | |

sbitmap visited; | |

int count; | |

if (include_entry_exit) | |

post_order[post_order_num++] = EXIT_BLOCK; | |

/* Allocate stack for back-tracking up CFG. */ | |

stack = XNEWVEC (edge_iterator, n_basic_blocks + 1); | |

sp = 0; | |

/* Allocate bitmap to track nodes that have been visited. */ | |

visited = sbitmap_alloc (last_basic_block); | |

/* None of the nodes in the CFG have been visited yet. */ | |

sbitmap_zero (visited); | |

/* Push the first edge on to the stack. */ | |

stack[sp++] = ei_start (ENTRY_BLOCK_PTR->succs); | |

while (sp) | |

{ | |

edge_iterator ei; | |

basic_block src; | |

basic_block dest; | |

/* Look at the edge on the top of the stack. */ | |

ei = stack[sp - 1]; | |

src = ei_edge (ei)->src; | |

dest = ei_edge (ei)->dest; | |

/* Check if the edge destination has been visited yet. */ | |

if (dest != EXIT_BLOCK_PTR && ! TEST_BIT (visited, dest->index)) | |

{ | |

/* Mark that we have visited the destination. */ | |

SET_BIT (visited, dest->index); | |

if (EDGE_COUNT (dest->succs) > 0) | |

/* Since the DEST node has been visited for the first | |

time, check its successors. */ | |

stack[sp++] = ei_start (dest->succs); | |

else | |

post_order[post_order_num++] = dest->index; | |

} | |

else | |

{ | |

if (ei_one_before_end_p (ei) && src != ENTRY_BLOCK_PTR) | |

post_order[post_order_num++] = src->index; | |

if (!ei_one_before_end_p (ei)) | |

ei_next (&stack[sp - 1]); | |

else | |

sp--; | |

} | |

} | |

if (include_entry_exit) | |

{ | |

post_order[post_order_num++] = ENTRY_BLOCK; | |

count = post_order_num; | |

} | |

else | |

count = post_order_num + 2; | |

/* Delete the unreachable blocks if some were found and we are | |

supposed to do it. */ | |

if (delete_unreachable && (count != n_basic_blocks)) | |

{ | |

basic_block b; | |

basic_block next_bb; | |

for (b = ENTRY_BLOCK_PTR->next_bb; b != EXIT_BLOCK_PTR; b = next_bb) | |

{ | |

next_bb = b->next_bb; | |

if (!(TEST_BIT (visited, b->index))) | |

delete_basic_block (b); | |

} | |

tidy_fallthru_edges (); | |

} | |

free (stack); | |

sbitmap_free (visited); | |

return post_order_num; | |

} | |

/* Helper routine for inverted_post_order_compute. | |

BB has to belong to a region of CFG | |

unreachable by inverted traversal from the exit. | |

i.e. there's no control flow path from ENTRY to EXIT | |

that contains this BB. | |

This can happen in two cases - if there's an infinite loop | |

or if there's a block that has no successor | |

(call to a function with no return). | |

Some RTL passes deal with this condition by | |

calling connect_infinite_loops_to_exit () and/or | |

add_noreturn_fake_exit_edges (). | |

However, those methods involve modifying the CFG itself | |

which may not be desirable. | |

Hence, we deal with the infinite loop/no return cases | |

by identifying a unique basic block that can reach all blocks | |

in such a region by inverted traversal. | |

This function returns a basic block that guarantees | |

that all blocks in the region are reachable | |

by starting an inverted traversal from the returned block. */ | |

static basic_block | |

dfs_find_deadend (basic_block bb) | |

{ | |

sbitmap visited = sbitmap_alloc (last_basic_block); | |

sbitmap_zero (visited); | |

for (;;) | |

{ | |

SET_BIT (visited, bb->index); | |

if (EDGE_COUNT (bb->succs) == 0 | |

|| TEST_BIT (visited, EDGE_SUCC (bb, 0)->dest->index)) | |

{ | |

sbitmap_free (visited); | |

return bb; | |

} | |

bb = EDGE_SUCC (bb, 0)->dest; | |

} | |

gcc_unreachable (); | |

} | |

/* Compute the reverse top sort order of the inverted CFG | |

i.e. starting from the exit block and following the edges backward | |

(from successors to predecessors). | |

This ordering can be used for forward dataflow problems among others. | |

This function assumes that all blocks in the CFG are reachable | |

from the ENTRY (but not necessarily from EXIT). | |

If there's an infinite loop, | |

a simple inverted traversal starting from the blocks | |

with no successors can't visit all blocks. | |

To solve this problem, we first do inverted traversal | |

starting from the blocks with no successor. | |

And if there's any block left that's not visited by the regular | |

inverted traversal from EXIT, | |

those blocks are in such problematic region. | |

Among those, we find one block that has | |

any visited predecessor (which is an entry into such a region), | |

and start looking for a "dead end" from that block | |

and do another inverted traversal from that block. */ | |

int | |

inverted_post_order_compute (int *post_order) | |

{ | |

basic_block bb; | |

edge_iterator *stack; | |

int sp; | |

int post_order_num = 0; | |

sbitmap visited; | |

/* Allocate stack for back-tracking up CFG. */ | |

stack = XNEWVEC (edge_iterator, n_basic_blocks + 1); | |

sp = 0; | |

/* Allocate bitmap to track nodes that have been visited. */ | |

visited = sbitmap_alloc (last_basic_block); | |

/* None of the nodes in the CFG have been visited yet. */ | |

sbitmap_zero (visited); | |

/* Put all blocks that have no successor into the initial work list. */ | |

FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb) | |

if (EDGE_COUNT (bb->succs) == 0) | |

{ | |

/* Push the initial edge on to the stack. */ | |

if (EDGE_COUNT (bb->preds) > 0) | |

{ | |

stack[sp++] = ei_start (bb->preds); | |

SET_BIT (visited, bb->index); | |

} | |

} | |

do | |

{ | |

bool has_unvisited_bb = false; | |

/* The inverted traversal loop. */ | |

while (sp) | |

{ | |

edge_iterator ei; | |

basic_block pred; | |

/* Look at the edge on the top of the stack. */ | |

ei = stack[sp - 1]; | |

bb = ei_edge (ei)->dest; | |

pred = ei_edge (ei)->src; | |

/* Check if the predecessor has been visited yet. */ | |

if (! TEST_BIT (visited, pred->index)) | |

{ | |

/* Mark that we have visited the destination. */ | |

SET_BIT (visited, pred->index); | |

if (EDGE_COUNT (pred->preds) > 0) | |

/* Since the predecessor node has been visited for the first | |

time, check its predecessors. */ | |

stack[sp++] = ei_start (pred->preds); | |

else | |

post_order[post_order_num++] = pred->index; | |

} | |

else | |

{ | |

if (bb != EXIT_BLOCK_PTR && ei_one_before_end_p (ei)) | |

post_order[post_order_num++] = bb->index; | |

if (!ei_one_before_end_p (ei)) | |

ei_next (&stack[sp - 1]); | |

else | |

sp--; | |

} | |

} | |

/* Detect any infinite loop and activate the kludge. | |

Note that this doesn't check EXIT_BLOCK itself | |

since EXIT_BLOCK is always added after the outer do-while loop. */ | |

FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR, next_bb) | |

if (!TEST_BIT (visited, bb->index)) | |

{ | |

has_unvisited_bb = true; | |

if (EDGE_COUNT (bb->preds) > 0) | |

{ | |

edge_iterator ei; | |

edge e; | |

basic_block visited_pred = NULL; | |

/* Find an already visited predecessor. */ | |

FOR_EACH_EDGE (e, ei, bb->preds) | |

{ | |

if (TEST_BIT (visited, e->src->index)) | |

visited_pred = e->src; | |

} | |

if (visited_pred) | |

{ | |

basic_block be = dfs_find_deadend (bb); | |

gcc_assert (be != NULL); | |

SET_BIT (visited, be->index); | |

stack[sp++] = ei_start (be->preds); | |

break; | |

} | |

} | |

} | |

if (has_unvisited_bb && sp == 0) | |

{ | |

/* No blocks are reachable from EXIT at all. | |

Find a dead-end from the ENTRY, and restart the iteration. */ | |

basic_block be = dfs_find_deadend (ENTRY_BLOCK_PTR); | |

gcc_assert (be != NULL); | |

SET_BIT (visited, be->index); | |

stack[sp++] = ei_start (be->preds); | |

} | |

/* The only case the below while fires is | |

when there's an infinite loop. */ | |

} | |

while (sp); | |

/* EXIT_BLOCK is always included. */ | |

post_order[post_order_num++] = EXIT_BLOCK; | |

free (stack); | |

sbitmap_free (visited); | |

return post_order_num; | |

} | |

/* Compute the depth first search order and store in the array | |

PRE_ORDER if nonzero, marking the nodes visited in VISITED. If | |

REV_POST_ORDER is nonzero, return the reverse completion number for each | |

node. Returns the number of nodes visited. A depth first search | |

tries to get as far away from the starting point as quickly as | |

possible. | |

pre_order is a really a preorder numbering of the graph. | |

rev_post_order is really a reverse postorder numbering of the graph. | |

*/ | |

int | |

pre_and_rev_post_order_compute (int *pre_order, int *rev_post_order, | |

bool include_entry_exit) | |

{ | |

edge_iterator *stack; | |

int sp; | |

int pre_order_num = 0; | |

int rev_post_order_num = n_basic_blocks - 1; | |

sbitmap visited; | |

/* Allocate stack for back-tracking up CFG. */ | |

stack = XNEWVEC (edge_iterator, n_basic_blocks + 1); | |

sp = 0; | |

if (include_entry_exit) | |

{ | |

if (pre_order) | |

pre_order[pre_order_num] = ENTRY_BLOCK; | |

pre_order_num++; | |

if (rev_post_order) | |

rev_post_order[rev_post_order_num--] = ENTRY_BLOCK; | |

} | |

else | |

rev_post_order_num -= NUM_FIXED_BLOCKS; | |

/* Allocate bitmap to track nodes that have been visited. */ | |

visited = sbitmap_alloc (last_basic_block); | |

/* None of the nodes in the CFG have been visited yet. */ | |

sbitmap_zero (visited); | |

/* Push the first edge on to the stack. */ | |

stack[sp++] = ei_start (ENTRY_BLOCK_PTR->succs); | |

while (sp) | |

{ | |

edge_iterator ei; | |

basic_block src; | |

basic_block dest; | |

/* Look at the edge on the top of the stack. */ | |

ei = stack[sp - 1]; | |

src = ei_edge (ei)->src; | |

dest = ei_edge (ei)->dest; | |

/* Check if the edge destination has been visited yet. */ | |

if (dest != EXIT_BLOCK_PTR && ! TEST_BIT (visited, dest->index)) | |

{ | |

/* Mark that we have visited the destination. */ | |

SET_BIT (visited, dest->index); | |

if (pre_order) | |

pre_order[pre_order_num] = dest->index; | |

pre_order_num++; | |

if (EDGE_COUNT (dest->succs) > 0) | |

/* Since the DEST node has been visited for the first | |

time, check its successors. */ | |

stack[sp++] = ei_start (dest->succs); | |

else if (rev_post_order) | |

/* There are no successors for the DEST node so assign | |

its reverse completion number. */ | |

rev_post_order[rev_post_order_num--] = dest->index; | |

} | |

else | |

{ | |

if (ei_one_before_end_p (ei) && src != ENTRY_BLOCK_PTR | |

&& rev_post_order) | |

/* There are no more successors for the SRC node | |

so assign its reverse completion number. */ | |

rev_post_order[rev_post_order_num--] = src->index; | |

if (!ei_one_before_end_p (ei)) | |

ei_next (&stack[sp - 1]); | |

else | |

sp--; | |

} | |

} | |

free (stack); | |

sbitmap_free (visited); | |

if (include_entry_exit) | |

{ | |

if (pre_order) | |

pre_order[pre_order_num] = EXIT_BLOCK; | |

pre_order_num++; | |

if (rev_post_order) | |

rev_post_order[rev_post_order_num--] = EXIT_BLOCK; | |

/* The number of nodes visited should be the number of blocks. */ | |

gcc_assert (pre_order_num == n_basic_blocks); | |

} | |

else | |

/* The number of nodes visited should be the number of blocks minus | |

the entry and exit blocks which are not visited here. */ | |

gcc_assert (pre_order_num == n_basic_blocks - NUM_FIXED_BLOCKS); | |

return pre_order_num; | |

} | |

/* Compute the depth first search order on the _reverse_ graph and | |

store in the array DFS_ORDER, marking the nodes visited in VISITED. | |

Returns the number of nodes visited. | |

The computation is split into three pieces: | |

flow_dfs_compute_reverse_init () creates the necessary data | |

structures. | |

flow_dfs_compute_reverse_add_bb () adds a basic block to the data | |

structures. The block will start the search. | |

flow_dfs_compute_reverse_execute () continues (or starts) the | |

search using the block on the top of the stack, stopping when the | |

stack is empty. | |

flow_dfs_compute_reverse_finish () destroys the necessary data | |

structures. | |

Thus, the user will probably call ..._init(), call ..._add_bb() to | |

add a beginning basic block to the stack, call ..._execute(), | |

possibly add another bb to the stack and again call ..._execute(), | |

..., and finally call _finish(). */ | |

/* Initialize the data structures used for depth-first search on the | |

reverse graph. If INITIALIZE_STACK is nonzero, the exit block is | |

added to the basic block stack. DATA is the current depth-first | |

search context. If INITIALIZE_STACK is nonzero, there is an | |

element on the stack. */ | |

static void | |

flow_dfs_compute_reverse_init (depth_first_search_ds data) | |

{ | |

/* Allocate stack for back-tracking up CFG. */ | |

data->stack = XNEWVEC (basic_block, n_basic_blocks); | |

data->sp = 0; | |

/* Allocate bitmap to track nodes that have been visited. */ | |

data->visited_blocks = sbitmap_alloc (last_basic_block); | |

/* None of the nodes in the CFG have been visited yet. */ | |

sbitmap_zero (data->visited_blocks); | |

return; | |

} | |

/* Add the specified basic block to the top of the dfs data | |

structures. When the search continues, it will start at the | |

block. */ | |

static void | |

flow_dfs_compute_reverse_add_bb (depth_first_search_ds data, basic_block bb) | |

{ | |

data->stack[data->sp++] = bb; | |

SET_BIT (data->visited_blocks, bb->index); | |

} | |

/* Continue the depth-first search through the reverse graph starting with the | |

block at the stack's top and ending when the stack is empty. Visited nodes | |

are marked. Returns an unvisited basic block, or NULL if there is none | |

available. */ | |

static basic_block | |

flow_dfs_compute_reverse_execute (depth_first_search_ds data, | |

basic_block last_unvisited) | |

{ | |

basic_block bb; | |

edge e; | |

edge_iterator ei; | |

while (data->sp > 0) | |

{ | |

bb = data->stack[--data->sp]; | |

/* Perform depth-first search on adjacent vertices. */ | |

FOR_EACH_EDGE (e, ei, bb->preds) | |

if (!TEST_BIT (data->visited_blocks, e->src->index)) | |

flow_dfs_compute_reverse_add_bb (data, e->src); | |

} | |

/* Determine if there are unvisited basic blocks. */ | |

FOR_BB_BETWEEN (bb, last_unvisited, NULL, prev_bb) | |

if (!TEST_BIT (data->visited_blocks, bb->index)) | |

return bb; | |

return NULL; | |

} | |

/* Destroy the data structures needed for depth-first search on the | |

reverse graph. */ | |

static void | |

flow_dfs_compute_reverse_finish (depth_first_search_ds data) | |

{ | |

free (data->stack); | |

sbitmap_free (data->visited_blocks); | |

} | |

/* Performs dfs search from BB over vertices satisfying PREDICATE; | |

if REVERSE, go against direction of edges. Returns number of blocks | |

found and their list in RSLT. RSLT can contain at most RSLT_MAX items. */ | |

int | |

dfs_enumerate_from (basic_block bb, int reverse, | |

bool (*predicate) (const_basic_block, const void *), | |

basic_block *rslt, int rslt_max, const void *data) | |

{ | |

basic_block *st, lbb; | |

int sp = 0, tv = 0; | |

unsigned size; | |

/* A bitmap to keep track of visited blocks. Allocating it each time | |

this function is called is not possible, since dfs_enumerate_from | |

is often used on small (almost) disjoint parts of cfg (bodies of | |

loops), and allocating a large sbitmap would lead to quadratic | |

behavior. */ | |

static sbitmap visited; | |

static unsigned v_size; | |

#define MARK_VISITED(BB) (SET_BIT (visited, (BB)->index)) | |

#define UNMARK_VISITED(BB) (RESET_BIT (visited, (BB)->index)) | |

#define VISITED_P(BB) (TEST_BIT (visited, (BB)->index)) | |

/* Resize the VISITED sbitmap if necessary. */ | |

size = last_basic_block; | |

if (size < 10) | |

size = 10; | |

if (!visited) | |

{ | |

visited = sbitmap_alloc (size); | |

sbitmap_zero (visited); | |

v_size = size; | |

} | |

else if (v_size < size) | |

{ | |

/* Ensure that we increase the size of the sbitmap exponentially. */ | |

if (2 * v_size > size) | |

size = 2 * v_size; | |

visited = sbitmap_resize (visited, size, 0); | |

v_size = size; | |

} | |

st = XCNEWVEC (basic_block, rslt_max); | |

rslt[tv++] = st[sp++] = bb; | |

MARK_VISITED (bb); | |

while (sp) | |

{ | |

edge e; | |

edge_iterator ei; | |

lbb = st[--sp]; | |

if (reverse) | |

{ | |

FOR_EACH_EDGE (e, ei, lbb->preds) | |

if (!VISITED_P (e->src) && predicate (e->src, data)) | |

{ | |

gcc_assert (tv != rslt_max); | |

rslt[tv++] = st[sp++] = e->src; | |

MARK_VISITED (e->src); | |

} | |

} | |

else | |

{ | |

FOR_EACH_EDGE (e, ei, lbb->succs) | |

if (!VISITED_P (e->dest) && predicate (e->dest, data)) | |

{ | |

gcc_assert (tv != rslt_max); | |

rslt[tv++] = st[sp++] = e->dest; | |

MARK_VISITED (e->dest); | |

} | |

} | |

} | |

free (st); | |

for (sp = 0; sp < tv; sp++) | |

UNMARK_VISITED (rslt[sp]); | |

return tv; | |

#undef MARK_VISITED | |

#undef UNMARK_VISITED | |

#undef VISITED_P | |

} | |

/* Compute dominance frontiers, ala Harvey, Ferrante, et al. | |

This algorithm can be found in Timothy Harvey's PhD thesis, at | |

http://www.cs.rice.edu/~harv/dissertation.pdf in the section on iterative | |

dominance algorithms. | |

First, we identify each join point, j (any node with more than one | |

incoming edge is a join point). | |

We then examine each predecessor, p, of j and walk up the dominator tree | |

starting at p. | |

We stop the walk when we reach j's immediate dominator - j is in the | |

dominance frontier of each of the nodes in the walk, except for j's | |

immediate dominator. Intuitively, all of the rest of j's dominators are | |

shared by j's predecessors as well. | |

Since they dominate j, they will not have j in their dominance frontiers. | |

The number of nodes touched by this algorithm is equal to the size | |

of the dominance frontiers, no more, no less. | |

*/ | |

static void | |

compute_dominance_frontiers_1 (bitmap *frontiers) | |

{ | |

edge p; | |

edge_iterator ei; | |

basic_block b; | |

FOR_EACH_BB (b) | |

{ | |

if (EDGE_COUNT (b->preds) >= 2) | |

{ | |

FOR_EACH_EDGE (p, ei, b->preds) | |

{ | |

basic_block runner = p->src; | |

basic_block domsb; | |

if (runner == ENTRY_BLOCK_PTR) | |

continue; | |

domsb = get_immediate_dominator (CDI_DOMINATORS, b); | |

while (runner != domsb) | |

{ | |

if (bitmap_bit_p (frontiers[runner->index], b->index)) | |

break; | |

bitmap_set_bit (frontiers[runner->index], | |

b->index); | |

runner = get_immediate_dominator (CDI_DOMINATORS, | |

runner); | |

} | |

} | |

} | |

} | |

} | |

void | |

compute_dominance_frontiers (bitmap *frontiers) | |

{ | |

timevar_push (TV_DOM_FRONTIERS); | |

compute_dominance_frontiers_1 (frontiers); | |

timevar_pop (TV_DOM_FRONTIERS); | |

} | |

/* Given a set of blocks with variable definitions (DEF_BLOCKS), | |

return a bitmap with all the blocks in the iterated dominance | |

frontier of the blocks in DEF_BLOCKS. DFS contains dominance | |

frontier information as returned by compute_dominance_frontiers. | |

The resulting set of blocks are the potential sites where PHI nodes | |

are needed. The caller is responsible for freeing the memory | |

allocated for the return value. */ | |

bitmap | |

compute_idf (bitmap def_blocks, bitmap *dfs) | |

{ | |

bitmap_iterator bi; | |

unsigned bb_index, i; | |

VEC(int,heap) *work_stack; | |

bitmap phi_insertion_points; | |

work_stack = VEC_alloc (int, heap, n_basic_blocks); | |

phi_insertion_points = BITMAP_ALLOC (NULL); | |

/* Seed the work list with all the blocks in DEF_BLOCKS. We use | |

VEC_quick_push here for speed. This is safe because we know that | |

the number of definition blocks is no greater than the number of | |

basic blocks, which is the initial capacity of WORK_STACK. */ | |

EXECUTE_IF_SET_IN_BITMAP (def_blocks, 0, bb_index, bi) | |

VEC_quick_push (int, work_stack, bb_index); | |

/* Pop a block off the worklist, add every block that appears in | |

the original block's DF that we have not already processed to | |

the worklist. Iterate until the worklist is empty. Blocks | |

which are added to the worklist are potential sites for | |

PHI nodes. */ | |

while (VEC_length (int, work_stack) > 0) | |

{ | |

bb_index = VEC_pop (int, work_stack); | |

/* Since the registration of NEW -> OLD name mappings is done | |

separately from the call to update_ssa, when updating the SSA | |

form, the basic blocks where new and/or old names are defined | |

may have disappeared by CFG cleanup calls. In this case, | |

we may pull a non-existing block from the work stack. */ | |

gcc_assert (bb_index < (unsigned) last_basic_block); | |

EXECUTE_IF_AND_COMPL_IN_BITMAP (dfs[bb_index], phi_insertion_points, | |

0, i, bi) | |

{ | |

/* Use a safe push because if there is a definition of VAR | |

in every basic block, then WORK_STACK may eventually have | |

more than N_BASIC_BLOCK entries. */ | |

VEC_safe_push (int, heap, work_stack, i); | |

bitmap_set_bit (phi_insertion_points, i); | |

} | |

} | |

VEC_free (int, heap, work_stack); | |

return phi_insertion_points; | |

} | |