| /* Generic SSA value propagation engine. |
| Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc. |
| Contributed by Diego Novillo <dnovillo@redhat.com> |
| |
| This file is part of GCC. |
| |
| GCC is free software; you can redistribute it and/or modify it |
| under the terms of the GNU General Public License as published by the |
| Free Software Foundation; either version 2, or (at your option) 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 COPYING. If not, write to the Free |
| Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA |
| 02110-1301, USA. */ |
| |
| #include "config.h" |
| #include "system.h" |
| #include "coretypes.h" |
| #include "tm.h" |
| #include "tree.h" |
| #include "flags.h" |
| #include "rtl.h" |
| #include "tm_p.h" |
| #include "ggc.h" |
| #include "basic-block.h" |
| #include "output.h" |
| #include "expr.h" |
| #include "function.h" |
| #include "diagnostic.h" |
| #include "timevar.h" |
| #include "tree-dump.h" |
| #include "tree-flow.h" |
| #include "tree-pass.h" |
| #include "tree-ssa-propagate.h" |
| #include "langhooks.h" |
| #include "varray.h" |
| #include "vec.h" |
| |
| /* This file implements a generic value propagation engine based on |
| the same propagation used by the SSA-CCP algorithm [1]. |
| |
| Propagation is performed by simulating the execution of every |
| statement that produces the value being propagated. Simulation |
| proceeds as follows: |
| |
| 1- Initially, all edges of the CFG are marked not executable and |
| the CFG worklist is seeded with all the statements in the entry |
| basic block (block 0). |
| |
| 2- Every statement S is simulated with a call to the call-back |
| function SSA_PROP_VISIT_STMT. This evaluation may produce 3 |
| results: |
| |
| SSA_PROP_NOT_INTERESTING: Statement S produces nothing of |
| interest and does not affect any of the work lists. |
| |
| SSA_PROP_VARYING: The value produced by S cannot be determined |
| at compile time. Further simulation of S is not required. |
| If S is a conditional jump, all the outgoing edges for the |
| block are considered executable and added to the work |
| list. |
| |
| SSA_PROP_INTERESTING: S produces a value that can be computed |
| at compile time. Its result can be propagated into the |
| statements that feed from S. Furthermore, if S is a |
| conditional jump, only the edge known to be taken is added |
| to the work list. Edges that are known not to execute are |
| never simulated. |
| |
| 3- PHI nodes are simulated with a call to SSA_PROP_VISIT_PHI. The |
| return value from SSA_PROP_VISIT_PHI has the same semantics as |
| described in #2. |
| |
| 4- Three work lists are kept. Statements are only added to these |
| lists if they produce one of SSA_PROP_INTERESTING or |
| SSA_PROP_VARYING. |
| |
| CFG_BLOCKS contains the list of blocks to be simulated. |
| Blocks are added to this list if their incoming edges are |
| found executable. |
| |
| VARYING_SSA_EDGES contains the list of statements that feed |
| from statements that produce an SSA_PROP_VARYING result. |
| These are simulated first to speed up processing. |
| |
| INTERESTING_SSA_EDGES contains the list of statements that |
| feed from statements that produce an SSA_PROP_INTERESTING |
| result. |
| |
| 5- Simulation terminates when all three work lists are drained. |
| |
| Before calling ssa_propagate, it is important to clear |
| DONT_SIMULATE_AGAIN for all the statements in the program that |
| should be simulated. This initialization allows an implementation |
| to specify which statements should never be simulated. |
| |
| It is also important to compute def-use information before calling |
| ssa_propagate. |
| |
| References: |
| |
| [1] Constant propagation with conditional branches, |
| Wegman and Zadeck, ACM TOPLAS 13(2):181-210. |
| |
| [2] Building an Optimizing Compiler, |
| Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9. |
| |
| [3] Advanced Compiler Design and Implementation, |
| Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */ |
| |
| /* Function pointers used to parameterize the propagation engine. */ |
| static ssa_prop_visit_stmt_fn ssa_prop_visit_stmt; |
| static ssa_prop_visit_phi_fn ssa_prop_visit_phi; |
| |
| /* Use the TREE_DEPRECATED bitflag to mark statements that have been |
| added to one of the SSA edges worklists. This flag is used to |
| avoid visiting statements unnecessarily when draining an SSA edge |
| worklist. If while simulating a basic block, we find a statement with |
| STMT_IN_SSA_EDGE_WORKLIST set, we clear it to prevent SSA edge |
| processing from visiting it again. */ |
| #define STMT_IN_SSA_EDGE_WORKLIST(T) TREE_DEPRECATED (T) |
| |
| /* A bitmap to keep track of executable blocks in the CFG. */ |
| static sbitmap executable_blocks; |
| |
| /* Array of control flow edges on the worklist. */ |
| static VEC(basic_block,heap) *cfg_blocks; |
| |
| static unsigned int cfg_blocks_num = 0; |
| static int cfg_blocks_tail; |
| static int cfg_blocks_head; |
| |
| static sbitmap bb_in_list; |
| |
| /* Worklist of SSA edges which will need reexamination as their |
| definition has changed. SSA edges are def-use edges in the SSA |
| web. For each D-U edge, we store the target statement or PHI node |
| U. */ |
| static GTY(()) VEC(tree,gc) *interesting_ssa_edges; |
| |
| /* Identical to INTERESTING_SSA_EDGES. For performance reasons, the |
| list of SSA edges is split into two. One contains all SSA edges |
| who need to be reexamined because their lattice value changed to |
| varying (this worklist), and the other contains all other SSA edges |
| to be reexamined (INTERESTING_SSA_EDGES). |
| |
| Since most values in the program are VARYING, the ideal situation |
| is to move them to that lattice value as quickly as possible. |
| Thus, it doesn't make sense to process any other type of lattice |
| value until all VARYING values are propagated fully, which is one |
| thing using the VARYING worklist achieves. In addition, if we |
| don't use a separate worklist for VARYING edges, we end up with |
| situations where lattice values move from |
| UNDEFINED->INTERESTING->VARYING instead of UNDEFINED->VARYING. */ |
| static GTY(()) VEC(tree,gc) *varying_ssa_edges; |
| |
| |
| /* Return true if the block worklist empty. */ |
| |
| static inline bool |
| cfg_blocks_empty_p (void) |
| { |
| return (cfg_blocks_num == 0); |
| } |
| |
| |
| /* Add a basic block to the worklist. The block must not be already |
| in the worklist, and it must not be the ENTRY or EXIT block. */ |
| |
| static void |
| cfg_blocks_add (basic_block bb) |
| { |
| /* APPLE LOCAL begin mainline */ |
| bool head = false; |
| |
| gcc_assert (bb != ENTRY_BLOCK_PTR && bb != EXIT_BLOCK_PTR); |
| gcc_assert (!TEST_BIT (bb_in_list, bb->index)); |
| |
| if (cfg_blocks_empty_p ()) |
| { |
| cfg_blocks_tail = cfg_blocks_head = 0; |
| cfg_blocks_num = 1; |
| } |
| else |
| { |
| cfg_blocks_num++; |
| if (cfg_blocks_num > VEC_length (basic_block, cfg_blocks)) |
| { |
| /* We have to grow the array now. Adjust to queue to occupy |
| the full space of the original array. We do not need to |
| initialize the newly allocated portion of the array |
| because we keep track of CFG_BLOCKS_HEAD and |
| CFG_BLOCKS_HEAD. */ |
| cfg_blocks_tail = VEC_length (basic_block, cfg_blocks); |
| cfg_blocks_head = 0; |
| VEC_safe_grow (basic_block, heap, cfg_blocks, 2 * cfg_blocks_tail); |
| } |
| /* Minor optimization: we prefer to see blocks with more |
| predecessors later, because there is more of a chance that |
| the incoming edges will be executable. */ |
| else if (EDGE_COUNT (bb->preds) |
| >= EDGE_COUNT (VEC_index (basic_block, cfg_blocks, |
| cfg_blocks_head)->preds)) |
| cfg_blocks_tail = ((cfg_blocks_tail + 1) |
| % VEC_length (basic_block, cfg_blocks)); |
| else |
| { |
| if (cfg_blocks_head == 0) |
| cfg_blocks_head = VEC_length (basic_block, cfg_blocks); |
| --cfg_blocks_head; |
| head = true; |
| } |
| } |
| |
| VEC_replace (basic_block, cfg_blocks, |
| head ? cfg_blocks_head : cfg_blocks_tail, |
| bb); |
| /* APPLE LOCAL end mainline */ |
| SET_BIT (bb_in_list, bb->index); |
| } |
| |
| |
| /* Remove a block from the worklist. */ |
| |
| static basic_block |
| cfg_blocks_get (void) |
| { |
| basic_block bb; |
| |
| bb = VEC_index (basic_block, cfg_blocks, cfg_blocks_head); |
| |
| gcc_assert (!cfg_blocks_empty_p ()); |
| gcc_assert (bb); |
| |
| cfg_blocks_head = ((cfg_blocks_head + 1) |
| % VEC_length (basic_block, cfg_blocks)); |
| --cfg_blocks_num; |
| RESET_BIT (bb_in_list, bb->index); |
| |
| return bb; |
| } |
| |
| |
| /* We have just defined a new value for VAR. If IS_VARYING is true, |
| add all immediate uses of VAR to VARYING_SSA_EDGES, otherwise add |
| them to INTERESTING_SSA_EDGES. */ |
| |
| static void |
| add_ssa_edge (tree var, bool is_varying) |
| { |
| imm_use_iterator iter; |
| use_operand_p use_p; |
| |
| FOR_EACH_IMM_USE_FAST (use_p, iter, var) |
| { |
| tree use_stmt = USE_STMT (use_p); |
| |
| if (!DONT_SIMULATE_AGAIN (use_stmt) |
| && !STMT_IN_SSA_EDGE_WORKLIST (use_stmt)) |
| { |
| STMT_IN_SSA_EDGE_WORKLIST (use_stmt) = 1; |
| if (is_varying) |
| VEC_safe_push (tree, gc, varying_ssa_edges, use_stmt); |
| else |
| VEC_safe_push (tree, gc, interesting_ssa_edges, use_stmt); |
| } |
| } |
| } |
| |
| |
| /* Add edge E to the control flow worklist. */ |
| |
| static void |
| add_control_edge (edge e) |
| { |
| basic_block bb = e->dest; |
| if (bb == EXIT_BLOCK_PTR) |
| return; |
| |
| /* If the edge had already been executed, skip it. */ |
| if (e->flags & EDGE_EXECUTABLE) |
| return; |
| |
| e->flags |= EDGE_EXECUTABLE; |
| |
| /* If the block is already in the list, we're done. */ |
| if (TEST_BIT (bb_in_list, bb->index)) |
| return; |
| |
| cfg_blocks_add (bb); |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| fprintf (dump_file, "Adding Destination of edge (%d -> %d) to worklist\n\n", |
| e->src->index, e->dest->index); |
| } |
| |
| |
| /* Simulate the execution of STMT and update the work lists accordingly. */ |
| |
| static void |
| simulate_stmt (tree stmt) |
| { |
| enum ssa_prop_result val = SSA_PROP_NOT_INTERESTING; |
| edge taken_edge = NULL; |
| tree output_name = NULL_TREE; |
| |
| /* Don't bother visiting statements that are already |
| considered varying by the propagator. */ |
| if (DONT_SIMULATE_AGAIN (stmt)) |
| return; |
| |
| if (TREE_CODE (stmt) == PHI_NODE) |
| { |
| val = ssa_prop_visit_phi (stmt); |
| output_name = PHI_RESULT (stmt); |
| } |
| else |
| val = ssa_prop_visit_stmt (stmt, &taken_edge, &output_name); |
| |
| if (val == SSA_PROP_VARYING) |
| { |
| DONT_SIMULATE_AGAIN (stmt) = 1; |
| |
| /* If the statement produced a new varying value, add the SSA |
| edges coming out of OUTPUT_NAME. */ |
| if (output_name) |
| add_ssa_edge (output_name, true); |
| |
| /* If STMT transfers control out of its basic block, add |
| all outgoing edges to the work list. */ |
| if (stmt_ends_bb_p (stmt)) |
| { |
| edge e; |
| edge_iterator ei; |
| basic_block bb = bb_for_stmt (stmt); |
| FOR_EACH_EDGE (e, ei, bb->succs) |
| add_control_edge (e); |
| } |
| } |
| else if (val == SSA_PROP_INTERESTING) |
| { |
| /* If the statement produced new value, add the SSA edges coming |
| out of OUTPUT_NAME. */ |
| if (output_name) |
| add_ssa_edge (output_name, false); |
| |
| /* If we know which edge is going to be taken out of this block, |
| add it to the CFG work list. */ |
| if (taken_edge) |
| add_control_edge (taken_edge); |
| } |
| } |
| |
| /* Process an SSA edge worklist. WORKLIST is the SSA edge worklist to |
| drain. This pops statements off the given WORKLIST and processes |
| them until there are no more statements on WORKLIST. |
| We take a pointer to WORKLIST because it may be reallocated when an |
| SSA edge is added to it in simulate_stmt. */ |
| |
| static void |
| process_ssa_edge_worklist (VEC(tree,gc) **worklist) |
| { |
| /* Drain the entire worklist. */ |
| while (VEC_length (tree, *worklist) > 0) |
| { |
| basic_block bb; |
| |
| /* Pull the statement to simulate off the worklist. */ |
| tree stmt = VEC_pop (tree, *worklist); |
| |
| /* If this statement was already visited by simulate_block, then |
| we don't need to visit it again here. */ |
| if (!STMT_IN_SSA_EDGE_WORKLIST (stmt)) |
| continue; |
| |
| /* STMT is no longer in a worklist. */ |
| STMT_IN_SSA_EDGE_WORKLIST (stmt) = 0; |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "\nSimulating statement (from ssa_edges): "); |
| print_generic_stmt (dump_file, stmt, dump_flags); |
| } |
| |
| bb = bb_for_stmt (stmt); |
| |
| /* PHI nodes are always visited, regardless of whether or not |
| the destination block is executable. Otherwise, visit the |
| statement only if its block is marked executable. */ |
| if (TREE_CODE (stmt) == PHI_NODE |
| || TEST_BIT (executable_blocks, bb->index)) |
| simulate_stmt (stmt); |
| } |
| } |
| |
| |
| /* Simulate the execution of BLOCK. Evaluate the statement associated |
| with each variable reference inside the block. */ |
| |
| static void |
| simulate_block (basic_block block) |
| { |
| tree phi; |
| |
| /* There is nothing to do for the exit block. */ |
| if (block == EXIT_BLOCK_PTR) |
| return; |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| fprintf (dump_file, "\nSimulating block %d\n", block->index); |
| |
| /* Always simulate PHI nodes, even if we have simulated this block |
| before. */ |
| for (phi = phi_nodes (block); phi; phi = PHI_CHAIN (phi)) |
| simulate_stmt (phi); |
| |
| /* If this is the first time we've simulated this block, then we |
| must simulate each of its statements. */ |
| if (!TEST_BIT (executable_blocks, block->index)) |
| { |
| block_stmt_iterator j; |
| unsigned int normal_edge_count; |
| edge e, normal_edge; |
| edge_iterator ei; |
| |
| /* Note that we have simulated this block. */ |
| SET_BIT (executable_blocks, block->index); |
| |
| for (j = bsi_start (block); !bsi_end_p (j); bsi_next (&j)) |
| { |
| tree stmt = bsi_stmt (j); |
| |
| /* If this statement is already in the worklist then |
| "cancel" it. The reevaluation implied by the worklist |
| entry will produce the same value we generate here and |
| thus reevaluating it again from the worklist is |
| pointless. */ |
| if (STMT_IN_SSA_EDGE_WORKLIST (stmt)) |
| STMT_IN_SSA_EDGE_WORKLIST (stmt) = 0; |
| |
| simulate_stmt (stmt); |
| } |
| |
| /* We can not predict when abnormal edges will be executed, so |
| once a block is considered executable, we consider any |
| outgoing abnormal edges as executable. |
| |
| At the same time, if this block has only one successor that is |
| reached by non-abnormal edges, then add that successor to the |
| worklist. */ |
| normal_edge_count = 0; |
| normal_edge = NULL; |
| FOR_EACH_EDGE (e, ei, block->succs) |
| { |
| if (e->flags & EDGE_ABNORMAL) |
| add_control_edge (e); |
| else |
| { |
| normal_edge_count++; |
| normal_edge = e; |
| } |
| } |
| |
| if (normal_edge_count == 1) |
| add_control_edge (normal_edge); |
| } |
| } |
| |
| |
| /* Initialize local data structures and work lists. */ |
| |
| static void |
| ssa_prop_init (void) |
| { |
| edge e; |
| edge_iterator ei; |
| basic_block bb; |
| size_t i; |
| |
| /* Worklists of SSA edges. */ |
| interesting_ssa_edges = VEC_alloc (tree, gc, 20); |
| varying_ssa_edges = VEC_alloc (tree, gc, 20); |
| |
| executable_blocks = sbitmap_alloc (last_basic_block); |
| sbitmap_zero (executable_blocks); |
| |
| bb_in_list = sbitmap_alloc (last_basic_block); |
| sbitmap_zero (bb_in_list); |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| dump_immediate_uses (dump_file); |
| |
| cfg_blocks = VEC_alloc (basic_block, heap, 20); |
| VEC_safe_grow (basic_block, heap, cfg_blocks, 20); |
| |
| /* Initialize the values for every SSA_NAME. */ |
| for (i = 1; i < num_ssa_names; i++) |
| if (ssa_name (i)) |
| SSA_NAME_VALUE (ssa_name (i)) = NULL_TREE; |
| |
| /* Initially assume that every edge in the CFG is not executable. |
| (including the edges coming out of ENTRY_BLOCK_PTR). */ |
| FOR_ALL_BB (bb) |
| { |
| block_stmt_iterator si; |
| |
| for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si)) |
| STMT_IN_SSA_EDGE_WORKLIST (bsi_stmt (si)) = 0; |
| |
| FOR_EACH_EDGE (e, ei, bb->succs) |
| e->flags &= ~EDGE_EXECUTABLE; |
| } |
| |
| /* Seed the algorithm by adding the successors of the entry block to the |
| edge worklist. */ |
| FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR->succs) |
| add_control_edge (e); |
| } |
| |
| |
| /* Free allocated storage. */ |
| |
| static void |
| ssa_prop_fini (void) |
| { |
| VEC_free (tree, gc, interesting_ssa_edges); |
| VEC_free (tree, gc, varying_ssa_edges); |
| VEC_free (basic_block, heap, cfg_blocks); |
| cfg_blocks = NULL; |
| sbitmap_free (bb_in_list); |
| sbitmap_free (executable_blocks); |
| } |
| |
| |
| /* Get the main expression from statement STMT. */ |
| |
| tree |
| get_rhs (tree stmt) |
| { |
| enum tree_code code = TREE_CODE (stmt); |
| |
| switch (code) |
| { |
| case RETURN_EXPR: |
| stmt = TREE_OPERAND (stmt, 0); |
| if (!stmt || TREE_CODE (stmt) != MODIFY_EXPR) |
| return stmt; |
| /* FALLTHRU */ |
| |
| case MODIFY_EXPR: |
| stmt = TREE_OPERAND (stmt, 1); |
| if (TREE_CODE (stmt) == WITH_SIZE_EXPR) |
| return TREE_OPERAND (stmt, 0); |
| else |
| return stmt; |
| |
| case COND_EXPR: |
| return COND_EXPR_COND (stmt); |
| case SWITCH_EXPR: |
| return SWITCH_COND (stmt); |
| case GOTO_EXPR: |
| return GOTO_DESTINATION (stmt); |
| case LABEL_EXPR: |
| return LABEL_EXPR_LABEL (stmt); |
| |
| default: |
| return stmt; |
| } |
| } |
| |
| |
| /* Set the main expression of *STMT_P to EXPR. If EXPR is not a valid |
| GIMPLE expression no changes are done and the function returns |
| false. */ |
| |
| bool |
| set_rhs (tree *stmt_p, tree expr) |
| { |
| tree stmt = *stmt_p, op; |
| enum tree_code code = TREE_CODE (expr); |
| stmt_ann_t ann; |
| tree var; |
| ssa_op_iter iter; |
| |
| /* Verify the constant folded result is valid gimple. */ |
| if (TREE_CODE_CLASS (code) == tcc_binary) |
| { |
| if (!is_gimple_val (TREE_OPERAND (expr, 0)) |
| || !is_gimple_val (TREE_OPERAND (expr, 1))) |
| return false; |
| } |
| else if (TREE_CODE_CLASS (code) == tcc_unary) |
| { |
| if (!is_gimple_val (TREE_OPERAND (expr, 0))) |
| return false; |
| } |
| else if (code == ADDR_EXPR) |
| { |
| if (TREE_CODE (TREE_OPERAND (expr, 0)) == ARRAY_REF |
| && !is_gimple_val (TREE_OPERAND (TREE_OPERAND (expr, 0), 1))) |
| return false; |
| } |
| else if (code == COMPOUND_EXPR |
| || code == MODIFY_EXPR) |
| return false; |
| |
| if (EXPR_HAS_LOCATION (stmt) |
| && EXPR_P (expr) |
| && ! EXPR_HAS_LOCATION (expr) |
| && TREE_SIDE_EFFECTS (expr) |
| && TREE_CODE (expr) != LABEL_EXPR) |
| SET_EXPR_LOCATION (expr, EXPR_LOCATION (stmt)); |
| |
| switch (TREE_CODE (stmt)) |
| { |
| case RETURN_EXPR: |
| op = TREE_OPERAND (stmt, 0); |
| if (TREE_CODE (op) != MODIFY_EXPR) |
| { |
| TREE_OPERAND (stmt, 0) = expr; |
| break; |
| } |
| stmt = op; |
| /* FALLTHRU */ |
| |
| case MODIFY_EXPR: |
| op = TREE_OPERAND (stmt, 1); |
| if (TREE_CODE (op) == WITH_SIZE_EXPR) |
| stmt = op; |
| TREE_OPERAND (stmt, 1) = expr; |
| break; |
| |
| case COND_EXPR: |
| if (!is_gimple_condexpr (expr)) |
| return false; |
| COND_EXPR_COND (stmt) = expr; |
| break; |
| case SWITCH_EXPR: |
| SWITCH_COND (stmt) = expr; |
| break; |
| case GOTO_EXPR: |
| GOTO_DESTINATION (stmt) = expr; |
| break; |
| case LABEL_EXPR: |
| LABEL_EXPR_LABEL (stmt) = expr; |
| break; |
| |
| default: |
| /* Replace the whole statement with EXPR. If EXPR has no side |
| effects, then replace *STMT_P with an empty statement. */ |
| ann = stmt_ann (stmt); |
| *stmt_p = TREE_SIDE_EFFECTS (expr) ? expr : build_empty_stmt (); |
| (*stmt_p)->common.ann = (tree_ann_t) ann; |
| |
| if (in_ssa_p |
| && TREE_SIDE_EFFECTS (expr)) |
| { |
| /* Fix all the SSA_NAMEs created by *STMT_P to point to its new |
| replacement. */ |
| FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_ALL_DEFS) |
| { |
| if (TREE_CODE (var) == SSA_NAME) |
| SSA_NAME_DEF_STMT (var) = *stmt_p; |
| } |
| } |
| break; |
| } |
| |
| return true; |
| } |
| |
| |
| /* Entry point to the propagation engine. |
| |
| VISIT_STMT is called for every statement visited. |
| VISIT_PHI is called for every PHI node visited. */ |
| |
| void |
| ssa_propagate (ssa_prop_visit_stmt_fn visit_stmt, |
| ssa_prop_visit_phi_fn visit_phi) |
| { |
| ssa_prop_visit_stmt = visit_stmt; |
| ssa_prop_visit_phi = visit_phi; |
| |
| ssa_prop_init (); |
| |
| /* Iterate until the worklists are empty. */ |
| while (!cfg_blocks_empty_p () |
| || VEC_length (tree, interesting_ssa_edges) > 0 |
| || VEC_length (tree, varying_ssa_edges) > 0) |
| { |
| if (!cfg_blocks_empty_p ()) |
| { |
| /* Pull the next block to simulate off the worklist. */ |
| basic_block dest_block = cfg_blocks_get (); |
| simulate_block (dest_block); |
| } |
| |
| /* In order to move things to varying as quickly as |
| possible,process the VARYING_SSA_EDGES worklist first. */ |
| process_ssa_edge_worklist (&varying_ssa_edges); |
| |
| /* Now process the INTERESTING_SSA_EDGES worklist. */ |
| process_ssa_edge_worklist (&interesting_ssa_edges); |
| } |
| |
| ssa_prop_fini (); |
| } |
| |
| |
| /* Return the first V_MAY_DEF or V_MUST_DEF operand for STMT. */ |
| |
| tree |
| first_vdef (tree stmt) |
| { |
| ssa_op_iter iter; |
| tree op; |
| |
| /* Simply return the first operand we arrive at. */ |
| FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_VIRTUAL_DEFS) |
| return (op); |
| |
| gcc_unreachable (); |
| } |
| |
| |
| /* Return true if STMT is of the form 'LHS = mem_ref', where 'mem_ref' |
| is a non-volatile pointer dereference, a structure reference or a |
| reference to a single _DECL. Ignore volatile memory references |
| because they are not interesting for the optimizers. */ |
| |
| bool |
| stmt_makes_single_load (tree stmt) |
| { |
| tree rhs; |
| |
| if (TREE_CODE (stmt) != MODIFY_EXPR) |
| return false; |
| |
| if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF|SSA_OP_VUSE)) |
| return false; |
| |
| rhs = TREE_OPERAND (stmt, 1); |
| STRIP_NOPS (rhs); |
| |
| return (!TREE_THIS_VOLATILE (rhs) |
| && (DECL_P (rhs) |
| || REFERENCE_CLASS_P (rhs))); |
| } |
| |
| |
| /* Return true if STMT is of the form 'mem_ref = RHS', where 'mem_ref' |
| is a non-volatile pointer dereference, a structure reference or a |
| reference to a single _DECL. Ignore volatile memory references |
| because they are not interesting for the optimizers. */ |
| |
| bool |
| stmt_makes_single_store (tree stmt) |
| { |
| tree lhs; |
| |
| if (TREE_CODE (stmt) != MODIFY_EXPR) |
| return false; |
| |
| if (ZERO_SSA_OPERANDS (stmt, SSA_OP_VMAYDEF|SSA_OP_VMUSTDEF)) |
| return false; |
| |
| lhs = TREE_OPERAND (stmt, 0); |
| STRIP_NOPS (lhs); |
| |
| return (!TREE_THIS_VOLATILE (lhs) |
| && (DECL_P (lhs) |
| || REFERENCE_CLASS_P (lhs))); |
| } |
| |
| |
| /* If STMT makes a single memory load and all the virtual use operands |
| have the same value in array VALUES, return it. Otherwise, return |
| NULL. */ |
| |
| prop_value_t * |
| get_value_loaded_by (tree stmt, prop_value_t *values) |
| { |
| ssa_op_iter i; |
| tree vuse; |
| prop_value_t *prev_val = NULL; |
| prop_value_t *val = NULL; |
| |
| FOR_EACH_SSA_TREE_OPERAND (vuse, stmt, i, SSA_OP_VIRTUAL_USES) |
| { |
| val = &values[SSA_NAME_VERSION (vuse)]; |
| if (prev_val && prev_val->value != val->value) |
| return NULL; |
| prev_val = val; |
| } |
| |
| return val; |
| } |
| |
| |
| /* Propagation statistics. */ |
| struct prop_stats_d |
| { |
| long num_const_prop; |
| long num_copy_prop; |
| long num_pred_folded; |
| }; |
| |
| static struct prop_stats_d prop_stats; |
| |
| /* Replace USE references in statement STMT with the values stored in |
| PROP_VALUE. Return true if at least one reference was replaced. If |
| REPLACED_ADDRESSES_P is given, it will be set to true if an address |
| constant was replaced. */ |
| |
| bool |
| replace_uses_in (tree stmt, bool *replaced_addresses_p, |
| prop_value_t *prop_value) |
| { |
| bool replaced = false; |
| use_operand_p use; |
| ssa_op_iter iter; |
| |
| FOR_EACH_SSA_USE_OPERAND (use, stmt, iter, SSA_OP_USE) |
| { |
| tree tuse = USE_FROM_PTR (use); |
| tree val = prop_value[SSA_NAME_VERSION (tuse)].value; |
| |
| if (val == tuse || val == NULL_TREE) |
| continue; |
| |
| if (TREE_CODE (stmt) == ASM_EXPR |
| && !may_propagate_copy_into_asm (tuse)) |
| continue; |
| |
| if (!may_propagate_copy (tuse, val)) |
| continue; |
| |
| if (TREE_CODE (val) != SSA_NAME) |
| prop_stats.num_const_prop++; |
| else |
| prop_stats.num_copy_prop++; |
| |
| propagate_value (use, val); |
| |
| replaced = true; |
| if (POINTER_TYPE_P (TREE_TYPE (tuse)) && replaced_addresses_p) |
| *replaced_addresses_p = true; |
| } |
| |
| return replaced; |
| } |
| |
| |
| /* Replace the VUSE references in statement STMT with the values |
| stored in PROP_VALUE. Return true if a reference was replaced. If |
| REPLACED_ADDRESSES_P is given, it will be set to true if an address |
| constant was replaced. |
| |
| Replacing VUSE operands is slightly more complex than replacing |
| regular USEs. We are only interested in two types of replacements |
| here: |
| |
| 1- If the value to be replaced is a constant or an SSA name for a |
| GIMPLE register, then we are making a copy/constant propagation |
| from a memory store. For instance, |
| |
| # a_3 = V_MAY_DEF <a_2> |
| a.b = x_1; |
| ... |
| # VUSE <a_3> |
| y_4 = a.b; |
| |
| This replacement is only possible iff STMT is an assignment |
| whose RHS is identical to the LHS of the statement that created |
| the VUSE(s) that we are replacing. Otherwise, we may do the |
| wrong replacement: |
| |
| # a_3 = V_MAY_DEF <a_2> |
| # b_5 = V_MAY_DEF <b_4> |
| *p = 10; |
| ... |
| # VUSE <b_5> |
| x_8 = b; |
| |
| Even though 'b_5' acquires the value '10' during propagation, |
| there is no way for the propagator to tell whether the |
| replacement is correct in every reached use, because values are |
| computed at definition sites. Therefore, when doing final |
| substitution of propagated values, we have to check each use |
| site. Since the RHS of STMT ('b') is different from the LHS of |
| the originating statement ('*p'), we cannot replace 'b' with |
| '10'. |
| |
| Similarly, when merging values from PHI node arguments, |
| propagators need to take care not to merge the same values |
| stored in different locations: |
| |
| if (...) |
| # a_3 = V_MAY_DEF <a_2> |
| a.b = 3; |
| else |
| # a_4 = V_MAY_DEF <a_2> |
| a.c = 3; |
| # a_5 = PHI <a_3, a_4> |
| |
| It would be wrong to propagate '3' into 'a_5' because that |
| operation merges two stores to different memory locations. |
| |
| |
| 2- If the value to be replaced is an SSA name for a virtual |
| register, then we simply replace each VUSE operand with its |
| value from PROP_VALUE. This is the same replacement done by |
| replace_uses_in. */ |
| |
| static bool |
| replace_vuses_in (tree stmt, bool *replaced_addresses_p, |
| prop_value_t *prop_value) |
| { |
| bool replaced = false; |
| ssa_op_iter iter; |
| use_operand_p vuse; |
| |
| if (stmt_makes_single_load (stmt)) |
| { |
| /* If STMT is an assignment whose RHS is a single memory load, |
| see if we are trying to propagate a constant or a GIMPLE |
| register (case #1 above). */ |
| prop_value_t *val = get_value_loaded_by (stmt, prop_value); |
| tree rhs = TREE_OPERAND (stmt, 1); |
| |
| if (val |
| && val->value |
| && (is_gimple_reg (val->value) |
| || is_gimple_min_invariant (val->value)) |
| && simple_cst_equal (rhs, val->mem_ref) == 1) |
| |
| { |
| /* If we are replacing a constant address, inform our |
| caller. */ |
| if (TREE_CODE (val->value) != SSA_NAME |
| && POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (stmt, 1))) |
| && replaced_addresses_p) |
| *replaced_addresses_p = true; |
| |
| /* We can only perform the substitution if the load is done |
| from the same memory location as the original store. |
| Since we already know that there are no intervening |
| stores between DEF_STMT and STMT, we only need to check |
| that the RHS of STMT is the same as the memory reference |
| propagated together with the value. */ |
| TREE_OPERAND (stmt, 1) = val->value; |
| |
| if (TREE_CODE (val->value) != SSA_NAME) |
| prop_stats.num_const_prop++; |
| else |
| prop_stats.num_copy_prop++; |
| |
| /* Since we have replaced the whole RHS of STMT, there |
| is no point in checking the other VUSEs, as they will |
| all have the same value. */ |
| return true; |
| } |
| } |
| |
| /* Otherwise, the values for every VUSE operand must be other |
| SSA_NAMEs that can be propagated into STMT. */ |
| FOR_EACH_SSA_USE_OPERAND (vuse, stmt, iter, SSA_OP_VIRTUAL_USES) |
| { |
| tree var = USE_FROM_PTR (vuse); |
| tree val = prop_value[SSA_NAME_VERSION (var)].value; |
| |
| if (val == NULL_TREE || var == val) |
| continue; |
| |
| /* Constants and copies propagated between real and virtual |
| operands are only possible in the cases handled above. They |
| should be ignored in any other context. */ |
| if (is_gimple_min_invariant (val) || is_gimple_reg (val)) |
| continue; |
| |
| propagate_value (vuse, val); |
| prop_stats.num_copy_prop++; |
| replaced = true; |
| } |
| |
| return replaced; |
| } |
| |
| |
| /* Replace propagated values into all the arguments for PHI using the |
| values from PROP_VALUE. */ |
| |
| static void |
| replace_phi_args_in (tree phi, prop_value_t *prop_value) |
| { |
| int i; |
| bool replaced = false; |
| tree prev_phi = NULL; |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| prev_phi = unshare_expr (phi); |
| |
| for (i = 0; i < PHI_NUM_ARGS (phi); i++) |
| { |
| tree arg = PHI_ARG_DEF (phi, i); |
| |
| if (TREE_CODE (arg) == SSA_NAME) |
| { |
| tree val = prop_value[SSA_NAME_VERSION (arg)].value; |
| |
| if (val && val != arg && may_propagate_copy (arg, val)) |
| { |
| if (TREE_CODE (val) != SSA_NAME) |
| prop_stats.num_const_prop++; |
| else |
| prop_stats.num_copy_prop++; |
| |
| propagate_value (PHI_ARG_DEF_PTR (phi, i), val); |
| replaced = true; |
| |
| /* If we propagated a copy and this argument flows |
| through an abnormal edge, update the replacement |
| accordingly. */ |
| if (TREE_CODE (val) == SSA_NAME |
| && PHI_ARG_EDGE (phi, i)->flags & EDGE_ABNORMAL) |
| SSA_NAME_OCCURS_IN_ABNORMAL_PHI (val) = 1; |
| } |
| } |
| } |
| |
| if (replaced && dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "Folded PHI node: "); |
| print_generic_stmt (dump_file, prev_phi, TDF_SLIM); |
| fprintf (dump_file, " into: "); |
| print_generic_stmt (dump_file, phi, TDF_SLIM); |
| fprintf (dump_file, "\n"); |
| } |
| } |
| |
| |
| /* If STMT has a predicate whose value can be computed using the value |
| range information computed by VRP, compute its value and return true. |
| Otherwise, return false. */ |
| |
| static bool |
| fold_predicate_in (tree stmt) |
| { |
| tree *pred_p = NULL; |
| bool modify_expr_p = false; |
| tree val; |
| |
| if (TREE_CODE (stmt) == MODIFY_EXPR |
| && COMPARISON_CLASS_P (TREE_OPERAND (stmt, 1))) |
| { |
| modify_expr_p = true; |
| pred_p = &TREE_OPERAND (stmt, 1); |
| } |
| else if (TREE_CODE (stmt) == COND_EXPR) |
| pred_p = &COND_EXPR_COND (stmt); |
| else |
| return false; |
| |
| val = vrp_evaluate_conditional (*pred_p, stmt); |
| if (val) |
| { |
| if (modify_expr_p) |
| val = fold_convert (TREE_TYPE (*pred_p), val); |
| |
| if (dump_file) |
| { |
| fprintf (dump_file, "Folding predicate "); |
| print_generic_expr (dump_file, *pred_p, 0); |
| fprintf (dump_file, " to "); |
| print_generic_expr (dump_file, val, 0); |
| fprintf (dump_file, "\n"); |
| } |
| |
| prop_stats.num_pred_folded++; |
| *pred_p = val; |
| return true; |
| } |
| |
| return false; |
| } |
| |
| |
| /* Perform final substitution and folding of propagated values. |
| |
| PROP_VALUE[I] contains the single value that should be substituted |
| at every use of SSA name N_I. If PROP_VALUE is NULL, no values are |
| substituted. |
| |
| If USE_RANGES_P is true, statements that contain predicate |
| expressions are evaluated with a call to vrp_evaluate_conditional. |
| This will only give meaningful results when called from tree-vrp.c |
| (the information used by vrp_evaluate_conditional is built by the |
| VRP pass). */ |
| |
| void |
| substitute_and_fold (prop_value_t *prop_value, bool use_ranges_p) |
| { |
| basic_block bb; |
| |
| if (prop_value == NULL && !use_ranges_p) |
| return; |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| fprintf (dump_file, "\nSubstituing values and folding statements\n\n"); |
| |
| memset (&prop_stats, 0, sizeof (prop_stats)); |
| |
| /* Substitute values in every statement of every basic block. */ |
| FOR_EACH_BB (bb) |
| { |
| block_stmt_iterator i; |
| tree phi; |
| |
| /* Propagate known values into PHI nodes. */ |
| if (prop_value) |
| for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) |
| replace_phi_args_in (phi, prop_value); |
| |
| for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i)) |
| { |
| bool replaced_address, did_replace; |
| tree prev_stmt = NULL; |
| tree stmt = bsi_stmt (i); |
| |
| /* Ignore ASSERT_EXPRs. They are used by VRP to generate |
| range information for names and they are discarded |
| afterwards. */ |
| if (TREE_CODE (stmt) == MODIFY_EXPR |
| && TREE_CODE (TREE_OPERAND (stmt, 1)) == ASSERT_EXPR) |
| continue; |
| |
| /* Replace the statement with its folded version and mark it |
| folded. */ |
| did_replace = false; |
| replaced_address = false; |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| prev_stmt = unshare_expr (stmt); |
| |
| /* If we have range information, see if we can fold |
| predicate expressions. */ |
| if (use_ranges_p) |
| did_replace = fold_predicate_in (stmt); |
| |
| if (prop_value) |
| { |
| /* Only replace real uses if we couldn't fold the |
| statement using value range information (value range |
| information is not collected on virtuals, so we only |
| need to check this for real uses). */ |
| if (!did_replace) |
| did_replace |= replace_uses_in (stmt, &replaced_address, |
| prop_value); |
| |
| did_replace |= replace_vuses_in (stmt, &replaced_address, |
| prop_value); |
| } |
| |
| /* If we made a replacement, fold and cleanup the statement. */ |
| if (did_replace) |
| { |
| tree old_stmt = stmt; |
| tree rhs; |
| |
| fold_stmt (bsi_stmt_ptr (i)); |
| stmt = bsi_stmt (i); |
| |
| /* If we folded a builtin function, we'll likely |
| need to rename VDEFs. */ |
| mark_new_vars_to_rename (stmt); |
| |
| /* If we cleaned up EH information from the statement, |
| remove EH edges. */ |
| if (maybe_clean_or_replace_eh_stmt (old_stmt, stmt)) |
| tree_purge_dead_eh_edges (bb); |
| |
| rhs = get_rhs (stmt); |
| if (TREE_CODE (rhs) == ADDR_EXPR) |
| recompute_tree_invariant_for_addr_expr (rhs); |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "Folded statement: "); |
| print_generic_stmt (dump_file, prev_stmt, TDF_SLIM); |
| fprintf (dump_file, " into: "); |
| print_generic_stmt (dump_file, stmt, TDF_SLIM); |
| fprintf (dump_file, "\n"); |
| } |
| } |
| |
| /* Some statements may be simplified using ranges. For |
| example, division may be replaced by shifts, modulo |
| replaced with bitwise and, etc. Do this after |
| substituting constants, folding, etc so that we're |
| presented with a fully propagated, canonicalized |
| statement. */ |
| if (use_ranges_p) |
| simplify_stmt_using_ranges (stmt); |
| |
| } |
| } |
| |
| if (dump_file && (dump_flags & TDF_STATS)) |
| { |
| fprintf (dump_file, "Constants propagated: %6ld\n", |
| prop_stats.num_const_prop); |
| fprintf (dump_file, "Copies propagated: %6ld\n", |
| prop_stats.num_copy_prop); |
| fprintf (dump_file, "Predicates folded: %6ld\n", |
| prop_stats.num_pred_folded); |
| } |
| } |
| |
| #include "gt-tree-ssa-propagate.h" |