/* Conditional constant propagation pass for the GNU compiler. Copyright (C) 2000, 2001, 2002, 2003 Free Software Foundation, Inc. Adapted from original RTL SSA-CCP by Daniel Berlin Adapted to GIMPLE trees by Diego Novillo 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, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ /* Conditional constant propagation. References: Constant propagation with conditional branches, Wegman and Zadeck, ACM TOPLAS 13(2):181-210. Building an Optimizing Compiler, Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9. Advanced Compiler Design and Implementation, Steven Muchnick, Morgan Kaufmann, 1997, Section 12.6 */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "errors.h" #include "ggc.h" #include "tree.h" #include "langhooks.h" /* These RTL headers are needed for basic-block.h. */ #include "rtl.h" #include "tm_p.h" #include "hard-reg-set.h" #include "basic-block.h" #include "diagnostic.h" #include "tree-inline.h" #include "tree-flow.h" #include "tree-gimple.h" #include "tree-dump.h" #include "tree-pass.h" #include "timevar.h" #include "expr.h" #include "flags.h" /* Possible lattice values. */ typedef enum { UNINITIALIZED = 0, UNDEFINED, CONSTANT, VARYING } latticevalue; /* Use the TREE_VISITED bitflag to mark statements and PHI nodes that have been deemed VARYING and shouldn't be simulated again. */ #define DONT_SIMULATE_AGAIN(T) TREE_VISITED (T) /* Main structure for CCP. Contains the lattice value and, if it's a constant, the constant value. */ typedef struct { latticevalue lattice_val; tree const_val; } value; /* A bitmap to keep track of executable blocks in the CFG. */ static sbitmap executable_blocks; /* Array of control flow edges on the worklist. */ static GTY(()) varray_type cfg_blocks = NULL; static unsigned int cfg_blocks_num = 0; static int cfg_blocks_tail; static int cfg_blocks_head; static sbitmap bb_in_list; /* This is used to track the current value of each variable. */ static value *value_vector; /* 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 edge, we store the definition statement or PHI node D. The destination nodes that need to be visited are accessed using immediate_uses (D). */ static GTY(()) varray_type ssa_edges; static void initialize (void); static void finalize (void); static void visit_phi_node (tree); static tree ccp_fold (tree); static value cp_lattice_meet (value, value); static void visit_stmt (tree); static void visit_cond_stmt (tree); static void visit_assignment (tree); static void add_var_to_ssa_edges_worklist (tree); static void add_outgoing_control_edges (basic_block); static void add_control_edge (edge); static void def_to_varying (tree); static void set_lattice_value (tree, value); static void simulate_block (basic_block); static void simulate_stmt (tree); static void substitute_and_fold (void); static value evaluate_stmt (tree); static void dump_lattice_value (FILE *, const char *, value); static bool replace_uses_in (tree, bool *); static latticevalue likely_value (tree); static tree get_rhs (tree); static void set_rhs (tree *, tree); static value *get_value (tree); static value get_default_value (tree); static tree ccp_fold_builtin (tree, tree); static bool get_strlen (tree, tree *, bitmap); static inline bool cfg_blocks_empty_p (void); static void cfg_blocks_add (basic_block); static basic_block cfg_blocks_get (void); static bool need_imm_uses_for (tree var); /* Main entry point for SSA Conditional Constant Propagation. FNDECL is the declaration for the function to optimize. On exit, VARS_TO_RENAME will contain the symbols that have been exposed by the propagation of ADDR_EXPR expressions into pointer dereferences and need to be renamed into SSA. PHASE indicates which dump file from the DUMP_FILES array to use when dumping debugging information. */ static void tree_ssa_ccp (void) { initialize (); /* Iterate until the worklists are empty. */ while (!cfg_blocks_empty_p () || VARRAY_ACTIVE_SIZE (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); } /* The SSA_EDGES worklist can get rather large. Go ahead and drain the entire worklist each iteration through this loop. */ while (VARRAY_ACTIVE_SIZE (ssa_edges) > 0) { /* Pull the statement to simulate off the worklist. */ tree stmt = VARRAY_TOP_TREE (ssa_edges); stmt_ann_t ann = stmt_ann (stmt); VARRAY_POP (ssa_edges); /* visit_stmt can "cancel" reevaluation of some statements. If it does, then in_ccp_worklist will be zero. */ if (ann->in_ccp_worklist) { ann->in_ccp_worklist = 0; simulate_stmt (stmt); } } } /* Now perform substitutions based on the known constant values. */ substitute_and_fold (); /* Now cleanup any unreachable code. */ cleanup_tree_cfg (); /* Free allocated memory. */ finalize (); /* Debugging dumps. */ if (dump_file && (dump_flags & TDF_DETAILS)) { dump_referenced_vars (dump_file); fprintf (dump_file, "\n\n"); } } static bool gate_ccp (void) { return flag_tree_ccp != 0; } struct tree_opt_pass pass_ccp = { "ccp", /* name */ gate_ccp, /* gate */ tree_ssa_ccp, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_TREE_CCP, /* tv_id */ PROP_cfg | PROP_ssa, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_rename_vars | TODO_ggc_collect | TODO_verify_ssa /* todo_flags_finish */ }; /* Get the constant value associated with variable VAR. */ static value * get_value (tree var) { value *val; #if defined ENABLE_CHECKING if (TREE_CODE (var) != SSA_NAME) abort (); #endif val = &value_vector[SSA_NAME_VERSION (var)]; if (val->lattice_val == UNINITIALIZED) *val = get_default_value (var); return val; } /* 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 = TREE_CHAIN (phi)) visit_phi_node (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; /* 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)) visit_stmt (bsi_stmt (j)); /* 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 (e = block->succ; e; e = e->succ_next) { 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); } } /* Follow the def-use edges for statement DEF_STMT and simulate all the statements reached by it. */ static void simulate_stmt (tree use_stmt) { basic_block use_bb = bb_for_stmt (use_stmt); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\nSimulating statement (from ssa_edges): "); print_generic_stmt (dump_file, use_stmt, dump_flags); } if (TREE_CODE (use_stmt) == PHI_NODE) { /* PHI nodes are always visited, regardless of whether or not the destination block is executable. */ visit_phi_node (use_stmt); } else if (TEST_BIT (executable_blocks, use_bb->index)) { /* Otherwise, visit the statement containing the use reached by DEF, only if the destination block is marked executable. */ visit_stmt (use_stmt); } } /* Perform final substitution and folding. After this pass the program should still be in SSA form. */ static void substitute_and_fold (void) { basic_block bb; if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\nSubstituing constants and folding statements\n\n"); /* Substitute constants in every statement of every basic block. */ FOR_EACH_BB (bb) { block_stmt_iterator i; tree phi; /* Propagate our known constants into PHI nodes. */ for (phi = phi_nodes (bb); phi; phi = TREE_CHAIN (phi)) { int i; for (i = 0; i < PHI_NUM_ARGS (phi); i++) { value *new_val; tree *orig_p = &PHI_ARG_DEF (phi, i); if (! SSA_VAR_P (*orig_p)) break; new_val = get_value (*orig_p); if (new_val->lattice_val == CONSTANT && may_propagate_copy (*orig_p, new_val->const_val)) *orig_p = new_val->const_val; } } for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i)) { bool replaced_address; tree stmt = bsi_stmt (i); /* Skip statements that have been folded already. */ if (stmt_modified_p (stmt) || !is_exec_stmt (stmt)) continue; /* Replace the statement with its folded version and mark it folded. */ if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Line %d: replaced ", get_lineno (stmt)); print_generic_stmt (dump_file, stmt, TDF_SLIM); } if (replace_uses_in (stmt, &replaced_address)) { bool changed = fold_stmt (bsi_stmt_ptr (i)); stmt = bsi_stmt(i); modify_stmt (stmt); /* If we folded a builtin function, we'll likely need to rename VDEFs. */ if (replaced_address || changed) mark_new_vars_to_rename (stmt, vars_to_rename); } if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, " with "); print_generic_stmt (dump_file, stmt, TDF_SLIM); fprintf (dump_file, "\n"); } } } } /* Loop through the PHI_NODE's parameters for BLOCK and compare their lattice values to determine PHI_NODE's lattice value. The value of a PHI node is determined calling cp_lattice_meet() with all the arguments of the PHI node that are incoming via executable edges. */ static void visit_phi_node (tree phi) { bool short_circuit = 0; value phi_val, *curr_val; int i; /* If the PHI node has already been deemed to be VARYING, don't simulate it again. */ if (DONT_SIMULATE_AGAIN (phi)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\nVisiting PHI node: "); print_generic_expr (dump_file, phi, dump_flags); } curr_val = get_value (PHI_RESULT (phi)); switch (curr_val->lattice_val) { case VARYING: if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\n Shortcircuit. Default of VARYING."); short_circuit = 1; break; case CONSTANT: phi_val = *curr_val; break; case UNDEFINED: case UNINITIALIZED: phi_val.lattice_val = UNDEFINED; phi_val.const_val = NULL_TREE; break; default: abort (); } /* If the variable is volatile or the variable is never referenced in a real operand, then consider the PHI node VARYING. */ if (short_circuit || TREE_THIS_VOLATILE (SSA_NAME_VAR (PHI_RESULT (phi)))) { phi_val.lattice_val = VARYING; phi_val.const_val = NULL; } else for (i = 0; i < PHI_NUM_ARGS (phi); i++) { /* Compute the meet operator over all the PHI arguments. */ edge e = PHI_ARG_EDGE (phi, i); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\n Argument #%d (%d -> %d %sexecutable)\n", i, e->src->index, e->dest->index, (e->flags & EDGE_EXECUTABLE) ? "" : "not "); } /* If the incoming edge is executable, Compute the meet operator for the existing value of the PHI node and the current PHI argument. */ if (e->flags & EDGE_EXECUTABLE) { tree rdef = PHI_ARG_DEF (phi, i); value *rdef_val, val; if (is_gimple_min_invariant (rdef)) { val.lattice_val = CONSTANT; val.const_val = rdef; rdef_val = &val; } else rdef_val = get_value (rdef); phi_val = cp_lattice_meet (phi_val, *rdef_val); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\t"); print_generic_expr (dump_file, rdef, dump_flags); dump_lattice_value (dump_file, "\tValue: ", *rdef_val); fprintf (dump_file, "\n"); } if (phi_val.lattice_val == VARYING) break; } } if (dump_file && (dump_flags & TDF_DETAILS)) { dump_lattice_value (dump_file, "\n PHI node value: ", phi_val); fprintf (dump_file, "\n\n"); } set_lattice_value (PHI_RESULT (phi), phi_val); if (phi_val.lattice_val == VARYING) DONT_SIMULATE_AGAIN (phi) = 1; } /* Compute the meet operator between VAL1 and VAL2: any M UNDEFINED = any any M VARYING = VARYING Ci M Cj = Ci if (i == j) Ci M Cj = VARYING if (i != j) */ static value cp_lattice_meet (value val1, value val2) { value result; /* any M UNDEFINED = any. */ if (val1.lattice_val == UNDEFINED) return val2; else if (val2.lattice_val == UNDEFINED) return val1; /* any M VARYING = VARYING. */ if (val1.lattice_val == VARYING || val2.lattice_val == VARYING) { result.lattice_val = VARYING; result.const_val = NULL_TREE; return result; } /* Ci M Cj = Ci if (i == j) Ci M Cj = VARYING if (i != j) */ if (simple_cst_equal (val1.const_val, val2.const_val) == 1) { result.lattice_val = CONSTANT; result.const_val = val1.const_val; } else { result.lattice_val = VARYING; result.const_val = NULL_TREE; } return result; } /* Evaluate statement STMT. If the statement produces an output value and its evaluation changes the lattice value of its output, do the following: - If the statement is an assignment, add all the SSA edges starting at this definition. - If the statement is a conditional branch: . If the statement evaluates to non-constant, add all edges to worklist. . If the statement is constant, add the edge executed as the result of the branch. */ static void visit_stmt (tree stmt) { size_t i; stmt_ann_t ann; def_optype defs; vdef_optype vdefs; /* If the statement has already been deemed to be VARYING, don't simulate it again. */ if (DONT_SIMULATE_AGAIN (stmt)) return; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "\nVisiting statement: "); print_generic_stmt (dump_file, stmt, TDF_SLIM); fprintf (dump_file, "\n"); } ann = stmt_ann (stmt); /* 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 (ann->in_ccp_worklist) ann->in_ccp_worklist = 0; /* Now examine the statement. If the statement is an assignment that produces a single output value, evaluate its RHS to see if the lattice value of its output has changed. */ if (TREE_CODE (stmt) == MODIFY_EXPR && TREE_CODE (TREE_OPERAND (stmt, 0)) == SSA_NAME) visit_assignment (stmt); /* Definitions made by statements other than assignments to SSA_NAMEs represent unknown modifications to their outputs. Mark them VARYING. */ else if (NUM_DEFS (defs = DEF_OPS (ann)) != 0) { DONT_SIMULATE_AGAIN (stmt) = 1; for (i = 0; i < NUM_DEFS (defs); i++) { tree def = DEF_OP (defs, i); def_to_varying (def); } } /* If STMT is a conditional branch, see if we can determine which branch will be taken. */ else if (TREE_CODE (stmt) == COND_EXPR || TREE_CODE (stmt) == SWITCH_EXPR) visit_cond_stmt (stmt); /* Any other kind of statement is not interesting for constant propagation and, therefore, not worth simulating. */ else { DONT_SIMULATE_AGAIN (stmt) = 1; /* If STMT is a computed goto, then mark all the output edges executable. */ if (computed_goto_p (stmt)) add_outgoing_control_edges (bb_for_stmt (stmt)); } /* Mark all VDEF operands VARYING. */ vdefs = VDEF_OPS (ann); for (i = 0; i < NUM_VDEFS (vdefs); i++) def_to_varying (VDEF_RESULT (vdefs, i)); } /* Visit the assignment statement STMT. Set the value of its LHS to the value computed by the RHS. */ static void visit_assignment (tree stmt) { value val; tree lhs, rhs; lhs = TREE_OPERAND (stmt, 0); rhs = TREE_OPERAND (stmt, 1); if (TREE_THIS_VOLATILE (SSA_NAME_VAR (lhs))) { /* Volatile variables are always VARYING. */ val.lattice_val = VARYING; val.const_val = NULL_TREE; } else if (TREE_CODE (rhs) == SSA_NAME) { /* For a simple copy operation, we copy the lattice values. */ value *nval = get_value (rhs); val = *nval; } else { /* Evaluate the statement. */ val = evaluate_stmt (stmt); } /* FIXME: Hack. If this was a definition of a bitfield, we need to widen the constant value into the type of the destination variable. This should not be necessary if GCC represented bitfields properly. */ { tree lhs = TREE_OPERAND (stmt, 0); if (val.lattice_val == CONSTANT && TREE_CODE (lhs) == COMPONENT_REF && DECL_BIT_FIELD (TREE_OPERAND (lhs, 1))) { tree w = widen_bitfield (val.const_val, TREE_OPERAND (lhs, 1), lhs); if (w && is_gimple_min_invariant (w)) val.const_val = w; else { val.lattice_val = VARYING; val.const_val = NULL; } } } /* Set the lattice value of the statement's output. */ set_lattice_value (lhs, val); if (val.lattice_val == VARYING) DONT_SIMULATE_AGAIN (stmt) = 1; } /* Visit the conditional statement STMT. If it evaluates to a constant value, mark outgoing edges appropriately. */ static void visit_cond_stmt (tree stmt) { edge e; value val; basic_block block; block = bb_for_stmt (stmt); val = evaluate_stmt (stmt); /* Find which edge out of the conditional block will be taken and add it to the worklist. If no single edge can be determined statically, add all outgoing edges from BLOCK. */ e = find_taken_edge (block, val.const_val); if (e) add_control_edge (e); else { DONT_SIMULATE_AGAIN (stmt) = 1; add_outgoing_control_edges (block); } } /* Add all the edges coming out of BB to the control flow worklist. */ static void add_outgoing_control_edges (basic_block bb) { edge e; for (e = bb->succ; e; e = e->succ_next) add_control_edge (e); } /* 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); } /* CCP specific front-end to the non-destructive constant folding routines. Attempt to simplify the RHS of STMT knowing that one or more operands are constants. If simplification is possible, return the simplified RHS, otherwise return the original RHS. */ static tree ccp_fold (tree stmt) { tree rhs = get_rhs (stmt); enum tree_code code = TREE_CODE (rhs); int kind = TREE_CODE_CLASS (code); tree retval = NULL_TREE; /* If the RHS is just a variable, then that variable must now have a constant value that we can return directly. */ if (TREE_CODE (rhs) == SSA_NAME) return get_value (rhs)->const_val; /* Unary operators. Note that we know the single operand must be a constant. So this should almost always return a simplified RHS. */ if (kind == '1') { /* Handle unary operators which can appear in GIMPLE form. */ tree op0 = TREE_OPERAND (rhs, 0); /* Simplify the operand down to a constant. */ if (TREE_CODE (op0) == SSA_NAME) { value *val = get_value (op0); if (val->lattice_val == CONSTANT) op0 = get_value (op0)->const_val; } retval = nondestructive_fold_unary_to_constant (code, TREE_TYPE (rhs), op0); /* If we folded, but did not create an invariant, then we can not use this expression. */ if (retval && ! is_gimple_min_invariant (retval)) return NULL; /* If we could not fold the expression, but the arguments are all constants and gimple values, then build and return the new expression. In some cases the new expression is still something we can use as a replacement for an argument. This happens with NOP conversions of types for example. In other cases the new expression can not be used as a replacement for an argument (as it would create non-gimple code). But the new expression can still be used to derive other constants. */ if (! retval && is_gimple_min_invariant (op0)) return build1 (code, TREE_TYPE (rhs), op0); } /* Binary and comparison operators. We know one or both of the operands are constants. */ else if (kind == '2' || kind == '<' || code == TRUTH_AND_EXPR || code == TRUTH_OR_EXPR || code == TRUTH_XOR_EXPR) { /* Handle binary and comparison operators that can appear in GIMPLE form. */ tree op0 = TREE_OPERAND (rhs, 0); tree op1 = TREE_OPERAND (rhs, 1); /* Simplify the operands down to constants when appropriate. */ if (TREE_CODE (op0) == SSA_NAME) { value *val = get_value (op0); if (val->lattice_val == CONSTANT) op0 = val->const_val; } if (TREE_CODE (op1) == SSA_NAME) { value *val = get_value (op1); if (val->lattice_val == CONSTANT) op1 = val->const_val; } retval = nondestructive_fold_binary_to_constant (code, TREE_TYPE (rhs), op0, op1); /* If we folded, but did not create an invariant, then we can not use this expression. */ if (retval && ! is_gimple_min_invariant (retval)) return NULL; /* If we could not fold the expression, but the arguments are all constants and gimple values, then build and return the new expression. In some cases the new expression is still something we can use as a replacement for an argument. This happens with NOP conversions of types for example. In other cases the new expression can not be used as a replacement for an argument (as it would create non-gimple code). But the new expression can still be used to derive other constants. */ if (! retval && is_gimple_min_invariant (op0) && is_gimple_min_invariant (op1)) return build (code, TREE_TYPE (rhs), op0, op1); } /* We may be able to fold away calls to builtin functions if their arguments are constants. */ else if (code == CALL_EXPR && TREE_CODE (TREE_OPERAND (rhs, 0)) == ADDR_EXPR && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0)) == FUNCTION_DECL) && DECL_BUILT_IN (TREE_OPERAND (TREE_OPERAND (rhs, 0), 0))) { use_optype uses = STMT_USE_OPS (stmt); if (NUM_USES (uses) != 0) { tree *orig; size_t i; /* Preserve the original values of every operand. */ orig = xmalloc (sizeof (tree) * NUM_USES (uses)); for (i = 0; i < NUM_USES (uses); i++) orig[i] = USE_OP (uses, i); /* Substitute operands with their values and try to fold. */ replace_uses_in (stmt, NULL); retval = fold_builtin (rhs); /* Restore operands to their original form. */ for (i = 0; i < NUM_USES (uses); i++) *(USE_OP_PTR (uses, i)) = orig[i]; free (orig); } } else return rhs; /* If we got a simplified form, see if we need to convert its type. */ if (retval) { if (TREE_TYPE (retval) != TREE_TYPE (rhs)) retval = convert (TREE_TYPE (rhs), retval); if (TREE_TYPE (retval) == TREE_TYPE (rhs)) return retval; } /* No simplification was possible. */ return rhs; } /* Evaluate statement STMT. */ static value evaluate_stmt (tree stmt) { value val; tree simplified; latticevalue likelyvalue = likely_value (stmt); /* If the statement is likely to have a CONSTANT result, then try to fold the statement to determine the constant value. */ if (likelyvalue == CONSTANT) simplified = ccp_fold (stmt); /* If the statement is likely to have a VARYING result, then do not bother folding the statement. */ else if (likelyvalue == VARYING) simplified = get_rhs (stmt); /* Otherwise the statement is likely to have an UNDEFINED value and there will be nothing to do. */ else simplified = NULL_TREE; if (simplified && is_gimple_min_invariant (simplified)) { /* The statement produced a constant value. */ val.lattice_val = CONSTANT; val.const_val = simplified; } else { /* The statement produced a nonconstant value. If the statement had undefined operands, then the result of the statement should be undefined. Else the result of the statement is VARYING. */ val.lattice_val = (likelyvalue == UNDEFINED ? UNDEFINED : VARYING); val.const_val = NULL_TREE; } return val; } /* Debugging dumps. */ static void dump_lattice_value (FILE *outf, const char *prefix, value val) { switch (val.lattice_val) { case UNDEFINED: fprintf (outf, "%sUNDEFINED", prefix); break; case VARYING: fprintf (outf, "%sVARYING", prefix); break; case CONSTANT: fprintf (outf, "%sCONSTANT ", prefix); print_generic_expr (outf, val.const_val, dump_flags); break; default: abort (); } } /* Given a constant value VAL for bitfield FIELD, and a destination variable VAR, return VAL appropriately widened to fit into VAR. If FIELD is wider than HOST_WIDE_INT, NULL is returned. */ tree widen_bitfield (tree val, tree field, tree var) { unsigned var_size, field_size; tree wide_val; unsigned HOST_WIDE_INT mask; unsigned i; var_size = TREE_INT_CST_LOW (TYPE_SIZE (TREE_TYPE ((var)))); field_size = TREE_INT_CST_LOW (DECL_SIZE (field)); /* Give up if either the bitfield or the variable are too wide. */ if (field_size > HOST_BITS_PER_WIDE_INT || var_size > HOST_BITS_PER_WIDE_INT) return NULL; #if defined ENABLE_CHECKING if (var_size < field_size) abort (); #endif /* If VAL is not an integer constant, then give up. */ if (TREE_CODE (val) != INTEGER_CST) return NULL; /* If the sign bit of the value is not set, or the field's type is unsigned, then just mask off the high order bits of the value. */ if ((TREE_INT_CST_LOW (val) & (1 << (field_size - 1))) == 0 || DECL_UNSIGNED (field)) { /* Zero extension. Build a mask with the lower 'field_size' bits set and a BIT_AND_EXPR node to clear the high order bits of the value. */ for (i = 0, mask = 0; i < field_size; i++) mask |= 1 << i; wide_val = build (BIT_AND_EXPR, TREE_TYPE (var), val, build_int_2 (mask, 0)); } else { /* Sign extension. Create a mask with the upper 'field_size' bits set and a BIT_IOR_EXPR to set the high order bits of the value. */ for (i = 0, mask = 0; i < (var_size - field_size); i++) mask |= 1 << (var_size - i - 1); wide_val = build (BIT_IOR_EXPR, TREE_TYPE (var), val, build_int_2 (mask, 0)); } return fold (wide_val); } /* Function indicating whether we ought to include information for 'var' when calculating immediate uses. */ static bool need_imm_uses_for (tree var) { return get_value (var)->lattice_val != VARYING; } /* Initialize local data structures and worklists for CCP. */ static void initialize (void) { edge e; basic_block bb; sbitmap virtual_var; /* Worklist of SSA edges. */ VARRAY_TREE_INIT (ssa_edges, 20, "ssa_edges"); executable_blocks = sbitmap_alloc (last_basic_block); sbitmap_zero (executable_blocks); bb_in_list = sbitmap_alloc (last_basic_block); sbitmap_zero (bb_in_list); value_vector = (value *) xmalloc (highest_ssa_version * sizeof (value)); memset (value_vector, 0, highest_ssa_version * sizeof (value)); /* 1 if ssa variable is used in a virtual variable context. */ virtual_var = sbitmap_alloc (highest_ssa_version); sbitmap_zero (virtual_var); /* Initialize default values and simulation flags for PHI nodes, statements and edges. */ FOR_EACH_BB (bb) { block_stmt_iterator i; tree stmt; stmt_ann_t ann; def_optype defs; vdef_optype vdefs; size_t x; int vary; /* Get the default value for each definition. */ for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i)) { vary = 0; stmt = bsi_stmt (i); get_stmt_operands (stmt); ann = stmt_ann (stmt); defs = DEF_OPS (ann); for (x = 0; x < NUM_DEFS (defs); x++) { tree def = DEF_OP (defs, x); if (get_value (def)->lattice_val == VARYING) vary = 1; } DONT_SIMULATE_AGAIN (stmt) = vary; /* Mark all VDEF operands VARYING. */ vdefs = VDEF_OPS (ann); for (x = 0; x < NUM_VDEFS (vdefs); x++) { tree res = VDEF_RESULT (vdefs, x); get_value (res)->lattice_val = VARYING; SET_BIT (virtual_var, SSA_NAME_VERSION (res)); } } for (e = bb->succ; e; e = e->succ_next) e->flags &= ~EDGE_EXECUTABLE; } /* Now process PHI nodes. */ FOR_EACH_BB (bb) { tree phi, var; int x; for (phi = phi_nodes (bb); phi; phi = TREE_CHAIN (phi)) { value *val; val = get_value (PHI_RESULT (phi)); if (val->lattice_val != VARYING) { for (x = 0; x < PHI_NUM_ARGS (phi); x++) { var = PHI_ARG_DEF (phi, x); /* If one argument is virtual, the result is virtual, and therefore varying. */ if (TREE_CODE (var) == SSA_NAME) { if (TEST_BIT (virtual_var, SSA_NAME_VERSION (var))) { val->lattice_val = VARYING; SET_BIT (virtual_var, SSA_NAME_VERSION (PHI_RESULT (phi))); break; } } } } DONT_SIMULATE_AGAIN (phi) = ((val->lattice_val == VARYING) ? 1 : 0); } } sbitmap_free (virtual_var); /* Compute immediate uses for variables we care about. */ compute_immediate_uses (TDFA_USE_OPS, need_imm_uses_for); if (dump_file && (dump_flags & TDF_DETAILS)) dump_immediate_uses (dump_file); VARRAY_BB_INIT (cfg_blocks, 20, "cfg_blocks"); /* Seed the algorithm by adding the successors of the entry block to the edge worklist. */ for (e = ENTRY_BLOCK_PTR->succ; e; e = e->succ_next) { if (e->dest != EXIT_BLOCK_PTR) { e->flags |= EDGE_EXECUTABLE; cfg_blocks_add (e->dest); } } } /* Free allocated storage. */ static void finalize (void) { ssa_edges = NULL; cfg_blocks = NULL; free (value_vector); sbitmap_free (bb_in_list); sbitmap_free (executable_blocks); free_df (); } /* Is the block worklist empty. */ static inline bool cfg_blocks_empty_p (void) { return (cfg_blocks_num == 0); } /* Add a basic block to the worklist. */ static void cfg_blocks_add (basic_block bb) { if (bb == ENTRY_BLOCK_PTR || bb == EXIT_BLOCK_PTR) return; if (TEST_BIT (bb_in_list, bb->index)) return; if (cfg_blocks_empty_p ()) { cfg_blocks_tail = cfg_blocks_head = 0; cfg_blocks_num = 1; } else { cfg_blocks_num++; if (cfg_blocks_num > VARRAY_SIZE (cfg_blocks)) { /* We have to grow the array now. Adjust to queue to occupy the full space of the original array. */ cfg_blocks_tail = VARRAY_SIZE (cfg_blocks); cfg_blocks_head = 0; VARRAY_GROW (cfg_blocks, 2 * VARRAY_SIZE (cfg_blocks)); } else cfg_blocks_tail = (cfg_blocks_tail + 1) % VARRAY_SIZE (cfg_blocks); } VARRAY_BB (cfg_blocks, cfg_blocks_tail) = bb; SET_BIT (bb_in_list, bb->index); } /* Remove a block from the worklist. */ static basic_block cfg_blocks_get (void) { basic_block bb; bb = VARRAY_BB (cfg_blocks, cfg_blocks_head); #ifdef ENABLE_CHECKING if (cfg_blocks_empty_p () || !bb) abort (); #endif cfg_blocks_head = (cfg_blocks_head + 1) % VARRAY_SIZE (cfg_blocks); --cfg_blocks_num; RESET_BIT (bb_in_list, bb->index); return bb; } /* We have just defined a new value for VAR. Add all immediate uses of VAR to the ssa_edges worklist. */ static void add_var_to_ssa_edges_worklist (tree var) { tree stmt = SSA_NAME_DEF_STMT (var); dataflow_t df = get_immediate_uses (stmt); int num_uses = num_immediate_uses (df); int i; for (i = 0; i < num_uses; i++) { tree use = immediate_use (df, i); if (!DONT_SIMULATE_AGAIN (use)) { stmt_ann_t ann = stmt_ann (use); if (ann->in_ccp_worklist == 0) { ann->in_ccp_worklist = 1; VARRAY_PUSH_TREE (ssa_edges, use); } } } } /* Set the lattice value for the variable VAR to VARYING. */ static void def_to_varying (tree var) { value val; val.lattice_val = VARYING; val.const_val = NULL_TREE; set_lattice_value (var, val); } /* Set the lattice value for variable VAR to VAL. */ static void set_lattice_value (tree var, value val) { value *old = get_value (var); #ifdef ENABLE_CHECKING if (val.lattice_val == UNDEFINED) { /* CONSTANT->UNDEFINED is never a valid state transition. */ if (old->lattice_val == CONSTANT) abort (); /* VARYING->UNDEFINED is generally not a valid state transition, except for values which are initialized to VARYING. */ if (old->lattice_val == VARYING && get_default_value (var).lattice_val != VARYING) abort (); } else if (val.lattice_val == CONSTANT) { /* VARYING -> CONSTANT is an invalid state transition, except for objects which start off in a VARYING state. */ if (old->lattice_val == VARYING && get_default_value (var).lattice_val != VARYING) abort (); } #endif /* If the constant for VAR has changed, then this VAR is really varying. */ if (old->lattice_val == CONSTANT && val.lattice_val == CONSTANT && !simple_cst_equal (old->const_val, val.const_val)) { val.lattice_val = VARYING; val.const_val = NULL_TREE; } if (old->lattice_val != val.lattice_val) { if (dump_file && (dump_flags & TDF_DETAILS)) { dump_lattice_value (dump_file, "Lattice value changed to ", val); fprintf (dump_file, ". Adding definition to SSA edges.\n"); } add_var_to_ssa_edges_worklist (var); *old = val; } } /* Replace USE references in statement STMT with their immediate reaching definition. 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. */ static bool replace_uses_in (tree stmt, bool *replaced_addresses_p) { bool replaced = false; use_optype uses; size_t i; if (replaced_addresses_p) *replaced_addresses_p = false; get_stmt_operands (stmt); uses = STMT_USE_OPS (stmt); for (i = 0; i < NUM_USES (uses); i++) { tree *use = USE_OP_PTR (uses, i); value *val = get_value (*use); if (val->lattice_val == CONSTANT) { *use = val->const_val; replaced = true; if (POINTER_TYPE_P (TREE_TYPE (*use)) && replaced_addresses_p) *replaced_addresses_p = true; } } return replaced; } /* Return the likely latticevalue for STMT. If STMT has no operands, then return CONSTANT. Else if any operands of STMT are undefined, then return UNDEFINED. Else if any operands of STMT are constants, then return CONSTANT. Else return VARYING. */ static latticevalue likely_value (tree stmt) { use_optype uses; size_t i; int found_constant = 0; stmt_ann_t ann; /* If the statement makes aliased loads or has volatile operands, it won't fold to a constant value. */ ann = stmt_ann (stmt); if (ann->makes_aliased_loads || ann->has_volatile_ops) return VARYING; /* A CALL_EXPR is assumed to be varying. This may be overly conservative, in the presence of const and pure calls. */ if (get_call_expr_in (stmt) != NULL_TREE) return VARYING; get_stmt_operands (stmt); uses = USE_OPS (ann); for (i = 0; i < NUM_USES (uses); i++) { tree use = USE_OP (uses, i); value *val = get_value (use); if (val->lattice_val == UNDEFINED) return UNDEFINED; if (val->lattice_val == CONSTANT) found_constant = 1; } return ((found_constant || !uses) ? CONSTANT : VARYING); } /* A subroutine of fold_stmt_r. Attempts to fold *(A+O) to A[X]. BASE is an array type. OFFSET is a byte displacement. ORIG_TYPE is the desired result type. */ static tree maybe_fold_offset_to_array_ref (tree base, tree offset, tree orig_type) { unsigned HOST_WIDE_INT lquo, lrem; HOST_WIDE_INT hquo, hrem; tree elt_size, min_idx, idx; tree array_type, elt_type; /* Ignore stupid user tricks of indexing non-array variables. */ array_type = TREE_TYPE (base); if (TREE_CODE (array_type) != ARRAY_TYPE) return NULL_TREE; elt_type = TREE_TYPE (array_type); if (!lang_hooks.types_compatible_p (orig_type, elt_type)) return NULL_TREE; /* Whee. Ignore indexing of variable sized types. */ elt_size = TYPE_SIZE_UNIT (elt_type); if (TREE_CODE (elt_size) != INTEGER_CST) return NULL_TREE; /* If the division isn't exact, then don't do anything. Equally invalid as the above indexing of non-array variables. */ if (div_and_round_double (TRUNC_DIV_EXPR, 1, TREE_INT_CST_LOW (offset), TREE_INT_CST_HIGH (offset), TREE_INT_CST_LOW (elt_size), TREE_INT_CST_HIGH (elt_size), &lquo, &hquo, &lrem, &hrem) || lrem || hrem) return NULL_TREE; idx = build_int_2_wide (lquo, hquo); /* Re-bias the index by the min index of the array type. */ min_idx = TYPE_DOMAIN (TREE_TYPE (base)); if (min_idx) { min_idx = TYPE_MIN_VALUE (min_idx); if (min_idx) { idx = convert (TREE_TYPE (min_idx), idx); if (!integer_zerop (min_idx)) idx = int_const_binop (PLUS_EXPR, idx, min_idx, 1); } } return build (ARRAY_REF, orig_type, base, idx); } /* A subroutine of fold_stmt_r. Attempts to fold *(S+O) to S.X. BASE is a record type. OFFSET is a byte displacement. ORIG_TYPE is the desired result type. */ /* ??? This doesn't handle class inheritance. */ static tree maybe_fold_offset_to_component_ref (tree record_type, tree base, tree offset, tree orig_type, bool base_is_ptr) { tree f, t, field_type, tail_array_field; if (TREE_CODE (record_type) != RECORD_TYPE && TREE_CODE (record_type) != UNION_TYPE && TREE_CODE (record_type) != QUAL_UNION_TYPE) return NULL_TREE; /* Short-circuit silly cases. */ if (lang_hooks.types_compatible_p (record_type, orig_type)) return NULL_TREE; tail_array_field = NULL_TREE; for (f = TYPE_FIELDS (record_type); f ; f = TREE_CHAIN (f)) { int cmp; if (TREE_CODE (f) != FIELD_DECL) continue; if (DECL_BIT_FIELD (f)) continue; if (TREE_CODE (DECL_FIELD_OFFSET (f)) != INTEGER_CST) continue; /* ??? Java creates "interesting" fields for representing base classes. They have no name, and have no context. With no context, we get into trouble with nonoverlapping_component_refs_p. Skip them. */ if (!DECL_FIELD_CONTEXT (f)) continue; /* The previous array field isn't at the end. */ tail_array_field = NULL_TREE; /* Check to see if this offset overlaps with the field. */ cmp = tree_int_cst_compare (DECL_FIELD_OFFSET (f), offset); if (cmp > 0) continue; field_type = TREE_TYPE (f); if (cmp < 0) { /* Don't care about offsets into the middle of scalars. */ if (!AGGREGATE_TYPE_P (field_type)) continue; /* Check for array at the end of the struct. This is often used as for flexible array members. We should be able to turn this into an array access anyway. */ if (TREE_CODE (field_type) == ARRAY_TYPE) tail_array_field = f; /* Check the end of the field against the offset. */ if (!DECL_SIZE_UNIT (f) || TREE_CODE (DECL_SIZE_UNIT (f)) != INTEGER_CST) continue; t = int_const_binop (MINUS_EXPR, offset, DECL_FIELD_OFFSET (f), 1); if (!tree_int_cst_lt (t, DECL_SIZE_UNIT (f))) continue; /* If we matched, then set offset to the displacement into this field. */ offset = t; } /* Here we exactly match the offset being checked. If the types match, then we can return that field. */ else if (lang_hooks.types_compatible_p (orig_type, field_type)) { if (base_is_ptr) base = build1 (INDIRECT_REF, record_type, base); t = build (COMPONENT_REF, field_type, base, f); return t; } /* Don't care about type-punning of scalars. */ else if (!AGGREGATE_TYPE_P (field_type)) return NULL_TREE; goto found; } if (!tail_array_field) return NULL_TREE; f = tail_array_field; field_type = TREE_TYPE (f); found: /* If we get here, we've got an aggregate field, and a possibly non-zero offset into them. Recurse and hope for a valid match. */ if (base_is_ptr) base = build1 (INDIRECT_REF, record_type, base); base = build (COMPONENT_REF, field_type, base, f); t = maybe_fold_offset_to_array_ref (base, offset, orig_type); if (t) return t; return maybe_fold_offset_to_component_ref (field_type, base, offset, orig_type, false); } /* A subroutine of fold_stmt_r. Attempt to simplify *(BASE+OFFSET). Return the simplified expression, or NULL if nothing could be done. */ static tree maybe_fold_stmt_indirect (tree expr, tree base, tree offset) { tree t; /* We may well have constructed a double-nested PLUS_EXPR via multiple substitutions. Fold that down to one. Remove NON_LVALUE_EXPRs that are sometimes added. */ base = fold (base); STRIP_NOPS (base); TREE_OPERAND (expr, 0) = base; /* One possibility is that the address reduces to a string constant. */ t = fold_read_from_constant_string (expr); if (t) return t; /* Add in any offset from a PLUS_EXPR. */ if (TREE_CODE (base) == PLUS_EXPR) { tree offset2; offset2 = TREE_OPERAND (base, 1); if (TREE_CODE (offset2) != INTEGER_CST) return NULL_TREE; base = TREE_OPERAND (base, 0); offset = int_const_binop (PLUS_EXPR, offset, offset2, 1); } if (TREE_CODE (base) == ADDR_EXPR) { /* Strip the ADDR_EXPR. */ base = TREE_OPERAND (base, 0); /* Try folding *(&B+O) to B[X]. */ t = maybe_fold_offset_to_array_ref (base, offset, TREE_TYPE (expr)); if (t) return t; /* Try folding *(&B+O) to B.X. */ t = maybe_fold_offset_to_component_ref (TREE_TYPE (base), base, offset, TREE_TYPE (expr), false); if (t) return t; /* Fold *&B to B. */ if (integer_zerop (offset)) return base; } else { /* We can get here for out-of-range string constant accesses, such as "_"[3]. Bail out of the entire substitution search and arrange for the entire statement to be replaced by a call to __builtin_trap. In all likelyhood this will all be constant-folded away, but in the meantime we can't leave with something that get_expr_operands can't understand. */ t = base; STRIP_NOPS (t); if (TREE_CODE (t) == ADDR_EXPR && TREE_CODE (TREE_OPERAND (t, 0)) == STRING_CST) { /* FIXME: Except that this causes problems elsewhere with dead code not being deleted, and we abort in the rtl expanders because we failed to remove some ssa_name. In the meantime, just return zero. */ /* FIXME2: This condition should be signaled by fold_read_from_constant_string directly, rather than re-checking for it here. */ return integer_zero_node; } /* Try folding *(B+O) to B->X. Still an improvement. */ if (POINTER_TYPE_P (TREE_TYPE (base))) { t = maybe_fold_offset_to_component_ref (TREE_TYPE (TREE_TYPE (base)), base, offset, TREE_TYPE (expr), true); if (t) return t; } } /* Otherwise we had an offset that we could not simplify. */ return NULL_TREE; } /* A subroutine of fold_stmt_r. EXPR is a PLUS_EXPR. A quaint feature extant in our address arithmetic is that there can be hidden type changes here. The type of the result need not be the same as the type of the input pointer. What we're after here is an expression of the form (T *)(&array + const) where the cast doesn't actually exist, but is implicit in the type of the PLUS_EXPR. We'd like to turn this into &array[x] which may be able to propagate further. */ static tree maybe_fold_stmt_addition (tree expr) { tree op0 = TREE_OPERAND (expr, 0); tree op1 = TREE_OPERAND (expr, 1); tree ptr_type = TREE_TYPE (expr); tree ptd_type; tree t; bool subtract = (TREE_CODE (expr) == MINUS_EXPR); /* We're only interested in pointer arithmetic. */ if (!POINTER_TYPE_P (ptr_type)) return NULL_TREE; /* Canonicalize the integral operand to op1. */ if (INTEGRAL_TYPE_P (TREE_TYPE (op0))) { if (subtract) return NULL_TREE; t = op0, op0 = op1, op1 = t; } /* It had better be a constant. */ if (TREE_CODE (op1) != INTEGER_CST) return NULL_TREE; /* The first operand should be an ADDR_EXPR. */ if (TREE_CODE (op0) != ADDR_EXPR) return NULL_TREE; op0 = TREE_OPERAND (op0, 0); /* If the first operand is an ARRAY_REF, expand it so that we can fold the offset into it. */ while (TREE_CODE (op0) == ARRAY_REF) { tree array_obj = TREE_OPERAND (op0, 0); tree array_idx = TREE_OPERAND (op0, 1); tree elt_type = TREE_TYPE (op0); tree elt_size = TYPE_SIZE_UNIT (elt_type); tree min_idx; if (TREE_CODE (array_idx) != INTEGER_CST) break; if (TREE_CODE (elt_size) != INTEGER_CST) break; /* Un-bias the index by the min index of the array type. */ min_idx = TYPE_DOMAIN (TREE_TYPE (array_obj)); if (min_idx) { min_idx = TYPE_MIN_VALUE (min_idx); if (min_idx) { array_idx = convert (TREE_TYPE (min_idx), array_idx); if (!integer_zerop (min_idx)) array_idx = int_const_binop (MINUS_EXPR, array_idx, min_idx, 0); } } /* Convert the index to a byte offset. */ array_idx = convert (sizetype, array_idx); array_idx = int_const_binop (MULT_EXPR, array_idx, elt_size, 0); /* Update the operands for the next round, or for folding. */ /* If we're manipulating unsigned types, then folding into negative values can produce incorrect results. Particularly if the type is smaller than the width of the pointer. */ if (subtract && TYPE_UNSIGNED (TREE_TYPE (op1)) && tree_int_cst_lt (array_idx, op1)) return NULL; op1 = int_const_binop (subtract ? MINUS_EXPR : PLUS_EXPR, array_idx, op1, 0); subtract = false; op0 = array_obj; } /* If we weren't able to fold the subtraction into another array reference, canonicalize the integer for passing to the array and component ref simplification functions. */ if (subtract) { if (TYPE_UNSIGNED (TREE_TYPE (op1))) return NULL; op1 = fold (build1 (NEGATE_EXPR, TREE_TYPE (op1), op1)); /* ??? In theory fold should always produce another integer. */ if (TREE_CODE (op1) != INTEGER_CST) return NULL; } ptd_type = TREE_TYPE (ptr_type); /* At which point we can try some of the same things as for indirects. */ t = maybe_fold_offset_to_array_ref (op0, op1, ptd_type); if (!t) t = maybe_fold_offset_to_component_ref (TREE_TYPE (op0), op0, op1, ptd_type, false); if (t) t = build1 (ADDR_EXPR, ptr_type, t); return t; } /* Subroutine of fold_stmt called via walk_tree. We perform several simplifications of EXPR_P, mostly having to do with pointer arithmetic. */ static tree fold_stmt_r (tree *expr_p, int *walk_subtrees, void *data) { bool *changed_p = data; tree expr = *expr_p, t; /* ??? It'd be nice if walk_tree had a pre-order option. */ switch (TREE_CODE (expr)) { case INDIRECT_REF: t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); if (t) return t; *walk_subtrees = 0; t = maybe_fold_stmt_indirect (expr, TREE_OPERAND (expr, 0), integer_zero_node); break; /* ??? Could handle ARRAY_REF here, as a variant of INDIRECT_REF. We'd only want to bother decomposing an existing ARRAY_REF if the base array is found to have another offset contained within. Otherwise we'd be wasting time. */ case ADDR_EXPR: t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); if (t) return t; *walk_subtrees = 0; /* Set TREE_INVARIANT properly so that the value is properly considered constant, and so gets propagated as expected. */ if (*changed_p) recompute_tree_invarant_for_addr_expr (expr); return NULL_TREE; case PLUS_EXPR: case MINUS_EXPR: t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); if (t) return t; t = walk_tree (&TREE_OPERAND (expr, 1), fold_stmt_r, data, NULL); if (t) return t; *walk_subtrees = 0; t = maybe_fold_stmt_addition (expr); break; case COMPONENT_REF: t = walk_tree (&TREE_OPERAND (expr, 0), fold_stmt_r, data, NULL); if (t) return t; *walk_subtrees = 0; /* Make sure the FIELD_DECL is actually a field in the type on the lhs. In cases with IMA it is possible that it came from another, equivalent type at this point. We have already checked the equivalence in this case. Match on type plus offset, to allow for unnamed fields. We won't necessarily get the corresponding field for unions; this is believed to be harmless. */ if ((current_file_decl && TREE_CHAIN (current_file_decl)) && (DECL_FIELD_CONTEXT (TREE_OPERAND (expr, 1)) != TREE_TYPE (TREE_OPERAND (expr, 0)))) { tree f; tree orig_field = TREE_OPERAND (expr, 1); tree orig_type = TREE_TYPE (orig_field); for (f = TYPE_FIELDS (TREE_TYPE (TREE_OPERAND (expr, 0))); f; f = TREE_CHAIN (f)) { if (lang_hooks.types_compatible_p (TREE_TYPE (f), orig_type) && tree_int_cst_compare (DECL_FIELD_BIT_OFFSET (f), DECL_FIELD_BIT_OFFSET (orig_field)) == 0 && tree_int_cst_compare (DECL_FIELD_OFFSET (f), DECL_FIELD_OFFSET (orig_field)) == 0) { TREE_OPERAND (expr, 1) = f; break; } } /* Fall through is an error; it will be detected in tree-sra. */ } break; default: return NULL_TREE; } if (t) { *expr_p = t; *changed_p = true; } return NULL_TREE; } /* Fold the statement pointed by STMT_P. In some cases, this function may replace the whole statement with a new one. Returns true iff folding makes any changes. */ bool fold_stmt (tree *stmt_p) { tree rhs, result, stmt; bool changed = false; stmt = *stmt_p; /* If we replaced constants and the statement makes pointer dereferences, then we may need to fold instances of *&VAR into VAR, etc. */ if (walk_tree (stmt_p, fold_stmt_r, &changed, NULL)) { *stmt_p = build_function_call_expr (implicit_built_in_decls[BUILT_IN_TRAP], NULL); return true; } rhs = get_rhs (stmt); if (!rhs) return changed; result = NULL_TREE; /* Check for builtins that CCP can handle using information not available in the generic fold routines. */ if (TREE_CODE (rhs) == CALL_EXPR) { tree callee = get_callee_fndecl (rhs); if (callee && DECL_BUILT_IN (callee)) result = ccp_fold_builtin (stmt, rhs); } /* If we couldn't fold the RHS, hand over to the generic fold routines. */ if (result == NULL_TREE) result = fold (rhs); /* Strip away useless type conversions. Both the NON_LVALUE_EXPR that may have been added by fold, and "useless" type conversions that might now be apparent due to propagation. */ STRIP_MAIN_TYPE_NOPS (result); STRIP_USELESS_TYPE_CONVERSION (result); if (result != rhs) { changed = true; set_rhs (stmt_p, result); } return changed; } /* Get the main expression from statement STMT. */ static tree get_rhs (tree stmt) { enum tree_code code = TREE_CODE (stmt); if (code == MODIFY_EXPR) return TREE_OPERAND (stmt, 1); if (code == COND_EXPR) return COND_EXPR_COND (stmt); else if (code == SWITCH_EXPR) return SWITCH_COND (stmt); else if (code == RETURN_EXPR) { if (!TREE_OPERAND (stmt, 0)) return NULL_TREE; if (TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR) return TREE_OPERAND (TREE_OPERAND (stmt, 0), 1); else return TREE_OPERAND (stmt, 0); } else if (code == GOTO_EXPR) return GOTO_DESTINATION (stmt); else if (code == LABEL_EXPR) return LABEL_EXPR_LABEL (stmt); else return stmt; } /* Set the main expression of *STMT_P to EXPR. */ static void set_rhs (tree *stmt_p, tree expr) { tree stmt = *stmt_p; enum tree_code code = TREE_CODE (stmt); if (code == MODIFY_EXPR) TREE_OPERAND (stmt, 1) = expr; else if (code == COND_EXPR) COND_EXPR_COND (stmt) = expr; else if (code == SWITCH_EXPR) SWITCH_COND (stmt) = expr; else if (code == RETURN_EXPR) { if (TREE_OPERAND (stmt, 0) && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR) TREE_OPERAND (TREE_OPERAND (stmt, 0), 1) = expr; else TREE_OPERAND (stmt, 0) = expr; } else if (code == GOTO_EXPR) GOTO_DESTINATION (stmt) = expr; else if (code == LABEL_EXPR) LABEL_EXPR_LABEL (stmt) = expr; else { /* Replace the whole statement with EXPR. If EXPR has no side effects, then replace *STMT_P with an empty statement. */ stmt_ann_t ann = stmt_ann (stmt); *stmt_p = TREE_SIDE_EFFECTS (expr) ? expr : build_empty_stmt (); (*stmt_p)->common.ann = (tree_ann) ann; if (TREE_SIDE_EFFECTS (expr)) { def_optype defs; vdef_optype vdefs; size_t i; /* Fix all the SSA_NAMEs created by *STMT_P to point to its new replacement. */ defs = DEF_OPS (ann); for (i = 0; i < NUM_DEFS (defs); i++) { tree var = DEF_OP (defs, i); if (TREE_CODE (var) == SSA_NAME) SSA_NAME_DEF_STMT (var) = *stmt_p; } vdefs = VDEF_OPS (ann); for (i = 0; i < NUM_VDEFS (vdefs); i++) { tree var = VDEF_RESULT (vdefs, i); if (TREE_CODE (var) == SSA_NAME) SSA_NAME_DEF_STMT (var) = *stmt_p; } } } } /* Return a default value for variable VAR using the following rules: 1- Global and static variables are considered VARYING, unless they are declared const. 2- Function arguments are considered VARYING. 3- Any other value is considered UNDEFINED. This is useful when considering PHI nodes. PHI arguments that are undefined do not change the constant value of the PHI node, which allows for more constants to be propagated. */ static value get_default_value (tree var) { value val; tree sym; if (TREE_CODE (var) == SSA_NAME) sym = SSA_NAME_VAR (var); else { #ifdef ENABLE_CHECKING if (!DECL_P (var)) abort (); #endif sym = var; } val.lattice_val = UNDEFINED; val.const_val = NULL_TREE; if (TREE_CODE (sym) == PARM_DECL || TREE_THIS_VOLATILE (sym)) { /* Function arguments and volatile variables are considered VARYING. */ val.lattice_val = VARYING; } else if (decl_function_context (sym) != current_function_decl || TREE_STATIC (sym)) { /* Globals and static variables are considered VARYING, unless they are declared 'const'. */ val.lattice_val = VARYING; if (TREE_READONLY (sym) && DECL_INITIAL (sym) && is_gimple_min_invariant (DECL_INITIAL (sym))) { val.lattice_val = CONSTANT; val.const_val = DECL_INITIAL (sym); } } else { enum tree_code code; tree stmt = SSA_NAME_DEF_STMT (var); if (!IS_EMPTY_STMT (stmt)) { code = TREE_CODE (stmt); if (code != MODIFY_EXPR && code != PHI_NODE) val.lattice_val = VARYING; } } return val; } /* Fold builtin call FN in statement STMT. If it cannot be folded into a constant, return NULL_TREE. Otherwise, return its constant value. */ static tree ccp_fold_builtin (tree stmt, tree fn) { tree result, strlen_val[2]; tree arglist = TREE_OPERAND (fn, 1), a; tree callee = get_callee_fndecl (fn); bitmap visited; int strlen_arg, i; /* Ignore MD builtins. */ if (DECL_BUILT_IN_CLASS (callee) == BUILT_IN_MD) return NULL_TREE; /* First try the generic builtin folder. If that succeeds, return the result directly. */ result = fold_builtin (fn); if (result) return result; /* If the builtin could not be folded, and it has no argument list, we're done. */ if (!arglist) return NULL_TREE; /* Limit the work only for builtins we know how to simplify. */ switch (DECL_FUNCTION_CODE (callee)) { case BUILT_IN_STRLEN: case BUILT_IN_FPUTS: case BUILT_IN_FPUTS_UNLOCKED: strlen_arg = 1; break; case BUILT_IN_STRCPY: case BUILT_IN_STRNCPY: strlen_arg = 2; break; default: return NULL_TREE; } /* Try to use the dataflow information gathered by the CCP process. */ visited = BITMAP_XMALLOC (); memset (strlen_val, 0, sizeof (strlen_val)); for (i = 0, a = arglist; strlen_arg; i++, strlen_arg >>= 1, a = TREE_CHAIN (a)) if (strlen_arg & 1) { bitmap_clear (visited); if (!get_strlen (TREE_VALUE (a), &strlen_val[i], visited)) strlen_val[i] = NULL_TREE; } BITMAP_XFREE (visited); /* FIXME. All this code looks dangerous in the sense that it might create non-gimple expressions. */ switch (DECL_FUNCTION_CODE (callee)) { case BUILT_IN_STRLEN: /* Convert from the internal "sizetype" type to "size_t". */ if (strlen_val[0] && size_type_node) { tree new = convert (size_type_node, strlen_val[0]); /* If the result is not a valid gimple value, or not a cast of a valid gimple value, then we can not use the result. */ if (is_gimple_val (new) || (is_gimple_cast (new) && is_gimple_val (TREE_OPERAND (new, 0)))) return new; else return NULL_TREE; } return strlen_val[0]; case BUILT_IN_STRCPY: if (strlen_val[1] && is_gimple_val (strlen_val[1])) return simplify_builtin_strcpy (arglist, strlen_val[1]); case BUILT_IN_STRNCPY: if (strlen_val[1] && is_gimple_val (strlen_val[1])) return simplify_builtin_strncpy (arglist, strlen_val[1]); case BUILT_IN_FPUTS: return simplify_builtin_fputs (arglist, TREE_CODE (stmt) != MODIFY_EXPR, 0, strlen_val[0]); case BUILT_IN_FPUTS_UNLOCKED: return simplify_builtin_fputs (arglist, TREE_CODE (stmt) != MODIFY_EXPR, 1, strlen_val[0]); default: abort (); } return NULL_TREE; } /* Return the string length of ARG in LENGTH. If ARG is an SSA name variable, follow its use-def chains. If LENGTH is not NULL and its value is not equal to the length we determine, or if we are unable to determine the length, return false. VISITED is a bitmap of visited variables. */ static bool get_strlen (tree arg, tree *length, bitmap visited) { tree var, def_stmt, val; if (TREE_CODE (arg) != SSA_NAME) { val = c_strlen (arg, 1); if (!val) return false; if (*length && simple_cst_equal (val, *length) != 1) return false; *length = val; return true; } /* If we were already here, break the infinite cycle. */ if (bitmap_bit_p (visited, SSA_NAME_VERSION (arg))) return true; bitmap_set_bit (visited, SSA_NAME_VERSION (arg)); var = arg; def_stmt = SSA_NAME_DEF_STMT (var); switch (TREE_CODE (def_stmt)) { case MODIFY_EXPR: { tree len, rhs; /* The RHS of the statement defining VAR must either have a constant length or come from another SSA_NAME with a constant length. */ rhs = TREE_OPERAND (def_stmt, 1); STRIP_NOPS (rhs); if (TREE_CODE (rhs) == SSA_NAME) return get_strlen (rhs, length, visited); /* See if the RHS is a constant length. */ len = c_strlen (rhs, 1); if (len) { if (*length && simple_cst_equal (len, *length) != 1) return false; *length = len; return true; } break; } case PHI_NODE: { /* All the arguments of the PHI node must have the same constant length. */ int i; for (i = 0; i < PHI_NUM_ARGS (def_stmt); i++) { tree arg = PHI_ARG_DEF (def_stmt, i); /* If this PHI has itself as an argument, we cannot determine the string length of this argument. However, if we can find a constant string length for the other PHI args then we can still be sure that this is a constant string length. So be optimistic and just continue with the next argument. */ if (arg == PHI_RESULT (def_stmt)) continue; if (!get_strlen (arg, length, visited)) return false; } return true; } default: break; } return false; } /* A simple pass that attempts to fold all builtin functions. This pass is run after we've propagated as many constants as we can. */ static void execute_fold_all_builtins (void) { basic_block bb; FOR_EACH_BB (bb) { block_stmt_iterator i; for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i)) { tree *stmtp = bsi_stmt_ptr (i); tree call = get_rhs (*stmtp); tree callee, result; if (!call || TREE_CODE (call) != CALL_EXPR) continue; callee = get_callee_fndecl (call); if (!callee || DECL_BUILT_IN_CLASS (callee) != BUILT_IN_NORMAL) continue; result = ccp_fold_builtin (*stmtp, call); if (!result) switch (DECL_FUNCTION_CODE (callee)) { case BUILT_IN_CONSTANT_P: /* Resolve __builtin_constant_p. If it hasn't been folded to integer_one_node by now, it's fairly certain that the value simply isn't constant. */ result = integer_zero_node; break; default: continue; } if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Simplified\n "); print_generic_stmt (dump_file, *stmtp, dump_flags); } set_rhs (stmtp, result); modify_stmt (*stmtp); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "to\n "); print_generic_stmt (dump_file, *stmtp, dump_flags); fprintf (dump_file, "\n"); } } } } struct tree_opt_pass pass_fold_builtins = { "fab", /* name */ NULL, /* gate */ execute_fold_all_builtins, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ 0, /* tv_id */ PROP_cfg | PROP_ssa, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ }; #include "gt-tree-ssa-ccp.h"