/* SSA Jump Threading Copyright (C) 2005-2014 Free Software Foundation, Inc. Contributed by Jeff Law This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see . */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "tree.h" #include "flags.h" #include "tm_p.h" #include "predict.h" #include "vec.h" #include "hashtab.h" #include "hash-set.h" #include "machmode.h" #include "hard-reg-set.h" #include "input.h" #include "function.h" #include "dominance.h" #include "basic-block.h" #include "cfgloop.h" #include "timevar.h" #include "dumpfile.h" #include "tree-ssa-alias.h" #include "internal-fn.h" #include "gimple-expr.h" #include "is-a.h" #include "gimple.h" #include "gimple-iterator.h" #include "gimple-ssa.h" #include "tree-cfg.h" #include "tree-phinodes.h" #include "ssa-iterators.h" #include "stringpool.h" #include "tree-ssanames.h" #include "tree-ssa-propagate.h" #include "tree-ssa-threadupdate.h" #include "langhooks.h" #include "params.h" #include "tree-ssa-threadedge.h" #include "builtins.h" /* To avoid code explosion due to jump threading, we limit the number of statements we are going to copy. This variable holds the number of statements currently seen that we'll have to copy as part of the jump threading process. */ static int stmt_count; /* Array to record value-handles per SSA_NAME. */ vec ssa_name_values; /* Set the value for the SSA name NAME to VALUE. */ void set_ssa_name_value (tree name, tree value) { if (SSA_NAME_VERSION (name) >= ssa_name_values.length ()) ssa_name_values.safe_grow_cleared (SSA_NAME_VERSION (name) + 1); if (value && TREE_OVERFLOW_P (value)) value = drop_tree_overflow (value); ssa_name_values[SSA_NAME_VERSION (name)] = value; } /* Initialize the per SSA_NAME value-handles array. Returns it. */ void threadedge_initialize_values (void) { gcc_assert (!ssa_name_values.exists ()); ssa_name_values.create (num_ssa_names); } /* Free the per SSA_NAME value-handle array. */ void threadedge_finalize_values (void) { ssa_name_values.release (); } /* Return TRUE if we may be able to thread an incoming edge into BB to an outgoing edge from BB. Return FALSE otherwise. */ bool potentially_threadable_block (basic_block bb) { gimple_stmt_iterator gsi; /* If BB has a single successor or a single predecessor, then there is no threading opportunity. */ if (single_succ_p (bb) || single_pred_p (bb)) return false; /* If BB does not end with a conditional, switch or computed goto, then there is no threading opportunity. */ gsi = gsi_last_bb (bb); if (gsi_end_p (gsi) || ! gsi_stmt (gsi) || (gimple_code (gsi_stmt (gsi)) != GIMPLE_COND && gimple_code (gsi_stmt (gsi)) != GIMPLE_GOTO && gimple_code (gsi_stmt (gsi)) != GIMPLE_SWITCH)) return false; return true; } /* Return the LHS of any ASSERT_EXPR where OP appears as the first argument to the ASSERT_EXPR and in which the ASSERT_EXPR dominates BB. If no such ASSERT_EXPR is found, return OP. */ static tree lhs_of_dominating_assert (tree op, basic_block bb, gimple stmt) { imm_use_iterator imm_iter; gimple use_stmt; use_operand_p use_p; FOR_EACH_IMM_USE_FAST (use_p, imm_iter, op) { use_stmt = USE_STMT (use_p); if (use_stmt != stmt && gimple_assign_single_p (use_stmt) && TREE_CODE (gimple_assign_rhs1 (use_stmt)) == ASSERT_EXPR && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == op && dominated_by_p (CDI_DOMINATORS, bb, gimple_bb (use_stmt))) { return gimple_assign_lhs (use_stmt); } } return op; } /* We record temporary equivalences created by PHI nodes or statements within the target block. Doing so allows us to identify more jump threading opportunities, even in blocks with side effects. We keep track of those temporary equivalences in a stack structure so that we can unwind them when we're done processing a particular edge. This routine handles unwinding the data structures. */ static void remove_temporary_equivalences (vec *stack) { while (stack->length () > 0) { tree prev_value, dest; dest = stack->pop (); /* A NULL value indicates we should stop unwinding, otherwise pop off the next entry as they're recorded in pairs. */ if (dest == NULL) break; prev_value = stack->pop (); set_ssa_name_value (dest, prev_value); } } /* Record a temporary equivalence, saving enough information so that we can restore the state of recorded equivalences when we're done processing the current edge. */ static void record_temporary_equivalence (tree x, tree y, vec *stack) { tree prev_x = SSA_NAME_VALUE (x); /* Y may be NULL if we are invalidating entries in the table. */ if (y && TREE_CODE (y) == SSA_NAME) { tree tmp = SSA_NAME_VALUE (y); y = tmp ? tmp : y; } set_ssa_name_value (x, y); stack->reserve (2); stack->quick_push (prev_x); stack->quick_push (x); } /* Record temporary equivalences created by PHIs at the target of the edge E. Record unwind information for the equivalences onto STACK. If a PHI which prevents threading is encountered, then return FALSE indicating we should not thread this edge, else return TRUE. If SRC_MAP/DST_MAP exist, then mark the source and destination SSA_NAMEs of any equivalences recorded. We use this to make invalidation after traversing back edges less painful. */ static bool record_temporary_equivalences_from_phis (edge e, vec *stack) { gimple_stmt_iterator gsi; /* Each PHI creates a temporary equivalence, record them. These are context sensitive equivalences and will be removed later. */ for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) { gimple phi = gsi_stmt (gsi); tree src = PHI_ARG_DEF_FROM_EDGE (phi, e); tree dst = gimple_phi_result (phi); /* If the desired argument is not the same as this PHI's result and it is set by a PHI in E->dest, then we can not thread through E->dest. */ if (src != dst && TREE_CODE (src) == SSA_NAME && gimple_code (SSA_NAME_DEF_STMT (src)) == GIMPLE_PHI && gimple_bb (SSA_NAME_DEF_STMT (src)) == e->dest) return false; /* We consider any non-virtual PHI as a statement since it count result in a constant assignment or copy operation. */ if (!virtual_operand_p (dst)) stmt_count++; record_temporary_equivalence (dst, src, stack); } return true; } /* Fold the RHS of an assignment statement and return it as a tree. May return NULL_TREE if no simplification is possible. */ static tree fold_assignment_stmt (gimple stmt) { enum tree_code subcode = gimple_assign_rhs_code (stmt); switch (get_gimple_rhs_class (subcode)) { case GIMPLE_SINGLE_RHS: return fold (gimple_assign_rhs1 (stmt)); case GIMPLE_UNARY_RHS: { tree lhs = gimple_assign_lhs (stmt); tree op0 = gimple_assign_rhs1 (stmt); return fold_unary (subcode, TREE_TYPE (lhs), op0); } case GIMPLE_BINARY_RHS: { tree lhs = gimple_assign_lhs (stmt); tree op0 = gimple_assign_rhs1 (stmt); tree op1 = gimple_assign_rhs2 (stmt); return fold_binary (subcode, TREE_TYPE (lhs), op0, op1); } case GIMPLE_TERNARY_RHS: { tree lhs = gimple_assign_lhs (stmt); tree op0 = gimple_assign_rhs1 (stmt); tree op1 = gimple_assign_rhs2 (stmt); tree op2 = gimple_assign_rhs3 (stmt); /* Sadly, we have to handle conditional assignments specially here, because fold expects all the operands of an expression to be folded before the expression itself is folded, but we can't just substitute the folded condition here. */ if (gimple_assign_rhs_code (stmt) == COND_EXPR) op0 = fold (op0); return fold_ternary (subcode, TREE_TYPE (lhs), op0, op1, op2); } default: gcc_unreachable (); } } /* A new value has been assigned to LHS. If necessary, invalidate any equivalences that are no longer valid. This includes invaliding LHS and any objects that are currently equivalent to LHS. Finding the objects that are currently marked as equivalent to LHS is a bit tricky. We could walk the ssa names and see if any have SSA_NAME_VALUE that is the same as LHS. That's expensive. However, it's far more efficient to look at the unwinding stack as that will have all context sensitive equivalences which are the only ones that we really have to worry about here. */ static void invalidate_equivalences (tree lhs, vec *stack) { /* The stack is an unwinding stack. If the current element is NULL then it's a "stop unwinding" marker. Else the current marker is the SSA_NAME with an equivalence and the prior entry in the stack is what the current element is equivalent to. */ for (int i = stack->length() - 1; i >= 0; i--) { /* Ignore the stop unwinding markers. */ if ((*stack)[i] == NULL) continue; /* We want to check the current value of stack[i] to see if it matches LHS. If so, then invalidate. */ if (SSA_NAME_VALUE ((*stack)[i]) == lhs) record_temporary_equivalence ((*stack)[i], NULL_TREE, stack); /* Remember, we're dealing with two elements in this case. */ i--; } /* And invalidate any known value for LHS itself. */ if (SSA_NAME_VALUE (lhs)) record_temporary_equivalence (lhs, NULL_TREE, stack); } /* Try to simplify each statement in E->dest, ultimately leading to a simplification of the COND_EXPR at the end of E->dest. Record unwind information for temporary equivalences onto STACK. Use SIMPLIFY (a pointer to a callback function) to further simplify statements using pass specific information. We might consider marking just those statements which ultimately feed the COND_EXPR. It's not clear if the overhead of bookkeeping would be recovered by trying to simplify fewer statements. If we are able to simplify a statement into the form SSA_NAME = (SSA_NAME | gimple invariant), then we can record a context sensitive equivalence which may help us simplify later statements in E->dest. */ static gimple record_temporary_equivalences_from_stmts_at_dest (edge e, vec *stack, tree (*simplify) (gimple, gimple), bool backedge_seen) { gimple stmt = NULL; gimple_stmt_iterator gsi; int max_stmt_count; max_stmt_count = PARAM_VALUE (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS); /* Walk through each statement in the block recording equivalences we discover. Note any equivalences we discover are context sensitive (ie, are dependent on traversing E) and must be unwound when we're finished processing E. */ for (gsi = gsi_start_bb (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) { tree cached_lhs = NULL; stmt = gsi_stmt (gsi); /* Ignore empty statements and labels. */ if (gimple_code (stmt) == GIMPLE_NOP || gimple_code (stmt) == GIMPLE_LABEL || is_gimple_debug (stmt)) continue; /* If the statement has volatile operands, then we assume we can not thread through this block. This is overly conservative in some ways. */ if (gimple_code (stmt) == GIMPLE_ASM && gimple_asm_volatile_p (stmt)) return NULL; /* If duplicating this block is going to cause too much code expansion, then do not thread through this block. */ stmt_count++; if (stmt_count > max_stmt_count) return NULL; /* If this is not a statement that sets an SSA_NAME to a new value, then do not try to simplify this statement as it will not simplify in any way that is helpful for jump threading. */ if ((gimple_code (stmt) != GIMPLE_ASSIGN || TREE_CODE (gimple_assign_lhs (stmt)) != SSA_NAME) && (gimple_code (stmt) != GIMPLE_CALL || gimple_call_lhs (stmt) == NULL_TREE || TREE_CODE (gimple_call_lhs (stmt)) != SSA_NAME)) { /* STMT might still have DEFS and we need to invalidate any known equivalences for them. Consider if STMT is a GIMPLE_ASM with one or more outputs that feeds a conditional inside a loop. We might derive an equivalence due to the conditional. */ tree op; ssa_op_iter iter; if (backedge_seen) FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_DEF) invalidate_equivalences (op, stack); continue; } /* The result of __builtin_object_size depends on all the arguments of a phi node. Temporarily using only one edge produces invalid results. For example if (x < 6) goto l; else goto l; l: r = PHI <&w[2].a[1](2), &a.a[6](3)> __builtin_object_size (r, 0) The result of __builtin_object_size is defined to be the maximum of remaining bytes. If we use only one edge on the phi, the result will change to be the remaining bytes for the corresponding phi argument. Similarly for __builtin_constant_p: r = PHI <1(2), 2(3)> __builtin_constant_p (r) Both PHI arguments are constant, but x ? 1 : 2 is still not constant. */ if (is_gimple_call (stmt)) { tree fndecl = gimple_call_fndecl (stmt); if (fndecl && (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_OBJECT_SIZE || DECL_FUNCTION_CODE (fndecl) == BUILT_IN_CONSTANT_P)) { if (backedge_seen) { tree lhs = gimple_get_lhs (stmt); invalidate_equivalences (lhs, stack); } continue; } } /* At this point we have a statement which assigns an RHS to an SSA_VAR on the LHS. We want to try and simplify this statement to expose more context sensitive equivalences which in turn may allow us to simplify the condition at the end of the loop. Handle simple copy operations as well as implied copies from ASSERT_EXPRs. */ if (gimple_assign_single_p (stmt) && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME) cached_lhs = gimple_assign_rhs1 (stmt); else if (gimple_assign_single_p (stmt) && TREE_CODE (gimple_assign_rhs1 (stmt)) == ASSERT_EXPR) cached_lhs = TREE_OPERAND (gimple_assign_rhs1 (stmt), 0); else { /* A statement that is not a trivial copy or ASSERT_EXPR. We're going to temporarily copy propagate the operands and see if that allows us to simplify this statement. */ tree *copy; ssa_op_iter iter; use_operand_p use_p; unsigned int num, i = 0; num = NUM_SSA_OPERANDS (stmt, (SSA_OP_USE | SSA_OP_VUSE)); copy = XCNEWVEC (tree, num); /* Make a copy of the uses & vuses into USES_COPY, then cprop into the operands. */ FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE | SSA_OP_VUSE) { tree tmp = NULL; tree use = USE_FROM_PTR (use_p); copy[i++] = use; if (TREE_CODE (use) == SSA_NAME) tmp = SSA_NAME_VALUE (use); if (tmp) SET_USE (use_p, tmp); } /* Try to fold/lookup the new expression. Inserting the expression into the hash table is unlikely to help. */ if (is_gimple_call (stmt)) cached_lhs = fold_call_stmt (stmt, false); else cached_lhs = fold_assignment_stmt (stmt); if (!cached_lhs || (TREE_CODE (cached_lhs) != SSA_NAME && !is_gimple_min_invariant (cached_lhs))) cached_lhs = (*simplify) (stmt, stmt); /* Restore the statement's original uses/defs. */ i = 0; FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE | SSA_OP_VUSE) SET_USE (use_p, copy[i++]); free (copy); } /* Record the context sensitive equivalence if we were able to simplify this statement. If we have traversed a backedge at some point during threading, then always enter something here. Either a real equivalence, or a NULL_TREE equivalence which is effectively invalidation of prior equivalences. */ if (cached_lhs && (TREE_CODE (cached_lhs) == SSA_NAME || is_gimple_min_invariant (cached_lhs))) record_temporary_equivalence (gimple_get_lhs (stmt), cached_lhs, stack); else if (backedge_seen) invalidate_equivalences (gimple_get_lhs (stmt), stack); } return stmt; } /* Once we have passed a backedge in the CFG when threading, we do not want to utilize edge equivalences for simplification purpose. They are no longer necessarily valid. We use this callback rather than the ones provided by DOM/VRP to achieve that effect. */ static tree dummy_simplify (gimple stmt1 ATTRIBUTE_UNUSED, gimple stmt2 ATTRIBUTE_UNUSED) { return NULL_TREE; } /* Simplify the control statement at the end of the block E->dest. To avoid allocating memory unnecessarily, a scratch GIMPLE_COND is available to use/clobber in DUMMY_COND. Use SIMPLIFY (a pointer to a callback function) to further simplify a condition using pass specific information. Return the simplified condition or NULL if simplification could not be performed. */ static tree simplify_control_stmt_condition (edge e, gimple stmt, gimple dummy_cond, tree (*simplify) (gimple, gimple), bool handle_dominating_asserts) { tree cond, cached_lhs; enum gimple_code code = gimple_code (stmt); /* For comparisons, we have to update both operands, then try to simplify the comparison. */ if (code == GIMPLE_COND) { tree op0, op1; enum tree_code cond_code; op0 = gimple_cond_lhs (stmt); op1 = gimple_cond_rhs (stmt); cond_code = gimple_cond_code (stmt); /* Get the current value of both operands. */ if (TREE_CODE (op0) == SSA_NAME) { for (int i = 0; i < 2; i++) { if (TREE_CODE (op0) == SSA_NAME && SSA_NAME_VALUE (op0)) op0 = SSA_NAME_VALUE (op0); else break; } } if (TREE_CODE (op1) == SSA_NAME) { for (int i = 0; i < 2; i++) { if (TREE_CODE (op1) == SSA_NAME && SSA_NAME_VALUE (op1)) op1 = SSA_NAME_VALUE (op1); else break; } } if (handle_dominating_asserts) { /* Now see if the operand was consumed by an ASSERT_EXPR which dominates E->src. If so, we want to replace the operand with the LHS of the ASSERT_EXPR. */ if (TREE_CODE (op0) == SSA_NAME) op0 = lhs_of_dominating_assert (op0, e->src, stmt); if (TREE_CODE (op1) == SSA_NAME) op1 = lhs_of_dominating_assert (op1, e->src, stmt); } /* We may need to canonicalize the comparison. For example, op0 might be a constant while op1 is an SSA_NAME. Failure to canonicalize will cause us to miss threading opportunities. */ if (tree_swap_operands_p (op0, op1, false)) { tree tmp; cond_code = swap_tree_comparison (cond_code); tmp = op0; op0 = op1; op1 = tmp; } /* Stuff the operator and operands into our dummy conditional expression. */ gimple_cond_set_code (dummy_cond, cond_code); gimple_cond_set_lhs (dummy_cond, op0); gimple_cond_set_rhs (dummy_cond, op1); /* We absolutely do not care about any type conversions we only care about a zero/nonzero value. */ fold_defer_overflow_warnings (); cached_lhs = fold_binary (cond_code, boolean_type_node, op0, op1); if (cached_lhs) while (CONVERT_EXPR_P (cached_lhs)) cached_lhs = TREE_OPERAND (cached_lhs, 0); fold_undefer_overflow_warnings ((cached_lhs && is_gimple_min_invariant (cached_lhs)), stmt, WARN_STRICT_OVERFLOW_CONDITIONAL); /* If we have not simplified the condition down to an invariant, then use the pass specific callback to simplify the condition. */ if (!cached_lhs || !is_gimple_min_invariant (cached_lhs)) cached_lhs = (*simplify) (dummy_cond, stmt); return cached_lhs; } if (code == GIMPLE_SWITCH) cond = gimple_switch_index (stmt); else if (code == GIMPLE_GOTO) cond = gimple_goto_dest (stmt); else gcc_unreachable (); /* We can have conditionals which just test the state of a variable rather than use a relational operator. These are simpler to handle. */ if (TREE_CODE (cond) == SSA_NAME) { cached_lhs = cond; /* Get the variable's current value from the equivalence chains. It is possible to get loops in the SSA_NAME_VALUE chains (consider threading the backedge of a loop where we have a loop invariant SSA_NAME used in the condition. */ if (cached_lhs) { for (int i = 0; i < 2; i++) { if (TREE_CODE (cached_lhs) == SSA_NAME && SSA_NAME_VALUE (cached_lhs)) cached_lhs = SSA_NAME_VALUE (cached_lhs); else break; } } /* If we're dominated by a suitable ASSERT_EXPR, then update CACHED_LHS appropriately. */ if (handle_dominating_asserts && TREE_CODE (cached_lhs) == SSA_NAME) cached_lhs = lhs_of_dominating_assert (cached_lhs, e->src, stmt); /* If we haven't simplified to an invariant yet, then use the pass specific callback to try and simplify it further. */ if (cached_lhs && ! is_gimple_min_invariant (cached_lhs)) cached_lhs = (*simplify) (stmt, stmt); } else cached_lhs = NULL; return cached_lhs; } /* Copy debug stmts from DEST's chain of single predecessors up to SRC, so that we don't lose the bindings as PHI nodes are introduced when DEST gains new predecessors. */ void propagate_threaded_block_debug_into (basic_block dest, basic_block src) { if (!MAY_HAVE_DEBUG_STMTS) return; if (!single_pred_p (dest)) return; gcc_checking_assert (dest != src); gimple_stmt_iterator gsi = gsi_after_labels (dest); int i = 0; const int alloc_count = 16; // ?? Should this be a PARAM? /* Estimate the number of debug vars overridden in the beginning of DEST, to tell how many we're going to need to begin with. */ for (gimple_stmt_iterator si = gsi; i * 4 <= alloc_count * 3 && !gsi_end_p (si); gsi_next (&si)) { gimple stmt = gsi_stmt (si); if (!is_gimple_debug (stmt)) break; i++; } auto_vec fewvars; hash_set *vars = NULL; /* If we're already starting with 3/4 of alloc_count, go for a hash_set, otherwise start with an unordered stack-allocated VEC. */ if (i * 4 > alloc_count * 3) vars = new hash_set; /* Now go through the initial debug stmts in DEST again, this time actually inserting in VARS or FEWVARS. Don't bother checking for duplicates in FEWVARS. */ for (gimple_stmt_iterator si = gsi; !gsi_end_p (si); gsi_next (&si)) { gimple stmt = gsi_stmt (si); if (!is_gimple_debug (stmt)) break; tree var; if (gimple_debug_bind_p (stmt)) var = gimple_debug_bind_get_var (stmt); else if (gimple_debug_source_bind_p (stmt)) var = gimple_debug_source_bind_get_var (stmt); else gcc_unreachable (); if (vars) vars->add (var); else fewvars.quick_push (var); } basic_block bb = dest; do { bb = single_pred (bb); for (gimple_stmt_iterator si = gsi_last_bb (bb); !gsi_end_p (si); gsi_prev (&si)) { gimple stmt = gsi_stmt (si); if (!is_gimple_debug (stmt)) continue; tree var; if (gimple_debug_bind_p (stmt)) var = gimple_debug_bind_get_var (stmt); else if (gimple_debug_source_bind_p (stmt)) var = gimple_debug_source_bind_get_var (stmt); else gcc_unreachable (); /* Discard debug bind overlaps. ??? Unlike stmts from src, copied into a new block that will precede BB, debug bind stmts in bypassed BBs may actually be discarded if they're overwritten by subsequent debug bind stmts, which might be a problem once we introduce stmt frontier notes or somesuch. Adding `&& bb == src' to the condition below will preserve all potentially relevant debug notes. */ if (vars && vars->add (var)) continue; else if (!vars) { int i = fewvars.length (); while (i--) if (fewvars[i] == var) break; if (i >= 0) continue; if (fewvars.length () < (unsigned) alloc_count) fewvars.quick_push (var); else { vars = new hash_set; for (i = 0; i < alloc_count; i++) vars->add (fewvars[i]); fewvars.release (); vars->add (var); } } stmt = gimple_copy (stmt); /* ??? Should we drop the location of the copy to denote they're artificial bindings? */ gsi_insert_before (&gsi, stmt, GSI_NEW_STMT); } } while (bb != src && single_pred_p (bb)); if (vars) delete vars; else if (fewvars.exists ()) fewvars.release (); } /* See if TAKEN_EDGE->dest is a threadable block with no side effecs (ie, it need not be duplicated as part of the CFG/SSA updating process). If it is threadable, add it to PATH and VISITED and recurse, ultimately returning TRUE from the toplevel call. Otherwise do nothing and return false. DUMMY_COND, HANDLE_DOMINATING_ASSERTS and SIMPLIFY are used to try and simplify the condition at the end of TAKEN_EDGE->dest. */ static bool thread_around_empty_blocks (edge taken_edge, gimple dummy_cond, bool handle_dominating_asserts, tree (*simplify) (gimple, gimple), bitmap visited, vec *path, bool *backedge_seen_p) { basic_block bb = taken_edge->dest; gimple_stmt_iterator gsi; gimple stmt; tree cond; /* The key property of these blocks is that they need not be duplicated when threading. Thus they can not have visible side effects such as PHI nodes. */ if (!gsi_end_p (gsi_start_phis (bb))) return false; /* Skip over DEBUG statements at the start of the block. */ gsi = gsi_start_nondebug_bb (bb); /* If the block has no statements, but does have a single successor, then it's just a forwarding block and we can thread through it trivially. However, note that just threading through empty blocks with single successors is not inherently profitable. For the jump thread to be profitable, we must avoid a runtime conditional. By taking the return value from the recursive call, we get the desired effect of returning TRUE when we found a profitable jump threading opportunity and FALSE otherwise. This is particularly important when this routine is called after processing a joiner block. Returning TRUE too aggressively in that case results in pointless duplication of the joiner block. */ if (gsi_end_p (gsi)) { if (single_succ_p (bb)) { taken_edge = single_succ_edge (bb); if (!bitmap_bit_p (visited, taken_edge->dest->index)) { jump_thread_edge *x = new jump_thread_edge (taken_edge, EDGE_NO_COPY_SRC_BLOCK); path->safe_push (x); bitmap_set_bit (visited, taken_edge->dest->index); *backedge_seen_p |= ((taken_edge->flags & EDGE_DFS_BACK) != 0); if (*backedge_seen_p) simplify = dummy_simplify; return thread_around_empty_blocks (taken_edge, dummy_cond, handle_dominating_asserts, simplify, visited, path, backedge_seen_p); } } /* We have a block with no statements, but multiple successors? */ return false; } /* The only real statements this block can have are a control flow altering statement. Anything else stops the thread. */ stmt = gsi_stmt (gsi); if (gimple_code (stmt) != GIMPLE_COND && gimple_code (stmt) != GIMPLE_GOTO && gimple_code (stmt) != GIMPLE_SWITCH) return false; /* If we have traversed a backedge, then we do not want to look at certain expressions in the table that can not be relied upon. Luckily the only code that looked at those expressions is the SIMPLIFY callback, which we replace if we can no longer use it. */ if (*backedge_seen_p) simplify = dummy_simplify; /* Extract and simplify the condition. */ cond = simplify_control_stmt_condition (taken_edge, stmt, dummy_cond, simplify, handle_dominating_asserts); /* If the condition can be statically computed and we have not already visited the destination edge, then add the taken edge to our thread path. */ if (cond && is_gimple_min_invariant (cond)) { taken_edge = find_taken_edge (bb, cond); if (bitmap_bit_p (visited, taken_edge->dest->index)) return false; bitmap_set_bit (visited, taken_edge->dest->index); jump_thread_edge *x = new jump_thread_edge (taken_edge, EDGE_NO_COPY_SRC_BLOCK); path->safe_push (x); *backedge_seen_p |= ((taken_edge->flags & EDGE_DFS_BACK) != 0); if (*backedge_seen_p) simplify = dummy_simplify; thread_around_empty_blocks (taken_edge, dummy_cond, handle_dominating_asserts, simplify, visited, path, backedge_seen_p); return true; } return false; } /* We are exiting E->src, see if E->dest ends with a conditional jump which has a known value when reached via E. E->dest can have arbitrary side effects which, if threading is successful, will be maintained. Special care is necessary if E is a back edge in the CFG as we may have already recorded equivalences for E->dest into our various tables, including the result of the conditional at the end of E->dest. Threading opportunities are severely limited in that case to avoid short-circuiting the loop incorrectly. DUMMY_COND is a shared cond_expr used by condition simplification as scratch, to avoid allocating memory. HANDLE_DOMINATING_ASSERTS is true if we should try to replace operands of the simplified condition with left-hand sides of ASSERT_EXPRs they are used in. STACK is used to undo temporary equivalences created during the walk of E->dest. SIMPLIFY is a pass-specific function used to simplify statements. Our caller is responsible for restoring the state of the expression and const_and_copies stacks. Positive return value is success. Zero return value is failure, but the block can still be duplicated as a joiner in a jump thread path, negative indicates the block should not be duplicated and thus is not suitable for a joiner in a jump threading path. */ static int thread_through_normal_block (edge e, gimple dummy_cond, bool handle_dominating_asserts, vec *stack, tree (*simplify) (gimple, gimple), vec *path, bitmap visited, bool *backedge_seen_p) { /* If we have traversed a backedge, then we do not want to look at certain expressions in the table that can not be relied upon. Luckily the only code that looked at those expressions is the SIMPLIFY callback, which we replace if we can no longer use it. */ if (*backedge_seen_p) simplify = dummy_simplify; /* PHIs create temporary equivalences. Note that if we found a PHI that made the block non-threadable, then we need to bubble that up to our caller in the same manner we do when we prematurely stop processing statements below. */ if (!record_temporary_equivalences_from_phis (e, stack)) return -1; /* Now walk each statement recording any context sensitive temporary equivalences we can detect. */ gimple stmt = record_temporary_equivalences_from_stmts_at_dest (e, stack, simplify, *backedge_seen_p); /* If we didn't look at all the statements, the most likely reason is there were too many and thus duplicating this block is not profitable. Also note if we do not look at all the statements, then we may not have invalidated equivalences that are no longer valid if we threaded around a loop. Thus we must signal to our caller that this block is not suitable for use as a joiner in a threading path. */ if (!stmt) return -1; /* If we stopped at a COND_EXPR or SWITCH_EXPR, see if we know which arm will be taken. */ if (gimple_code (stmt) == GIMPLE_COND || gimple_code (stmt) == GIMPLE_GOTO || gimple_code (stmt) == GIMPLE_SWITCH) { tree cond; /* Extract and simplify the condition. */ cond = simplify_control_stmt_condition (e, stmt, dummy_cond, simplify, handle_dominating_asserts); if (cond && is_gimple_min_invariant (cond)) { edge taken_edge = find_taken_edge (e->dest, cond); basic_block dest = (taken_edge ? taken_edge->dest : NULL); /* DEST could be NULL for a computed jump to an absolute address. */ if (dest == NULL || dest == e->dest || bitmap_bit_p (visited, dest->index)) return 0; /* Only push the EDGE_START_JUMP_THREAD marker if this is first edge on the path. */ if (path->length () == 0) { jump_thread_edge *x = new jump_thread_edge (e, EDGE_START_JUMP_THREAD); path->safe_push (x); *backedge_seen_p |= ((e->flags & EDGE_DFS_BACK) != 0); } jump_thread_edge *x = new jump_thread_edge (taken_edge, EDGE_COPY_SRC_BLOCK); path->safe_push (x); *backedge_seen_p |= ((taken_edge->flags & EDGE_DFS_BACK) != 0); if (*backedge_seen_p) simplify = dummy_simplify; /* See if we can thread through DEST as well, this helps capture secondary effects of threading without having to re-run DOM or VRP. We don't want to thread back to a block we have already visited. This may be overly conservative. */ bitmap_set_bit (visited, dest->index); bitmap_set_bit (visited, e->dest->index); thread_around_empty_blocks (taken_edge, dummy_cond, handle_dominating_asserts, simplify, visited, path, backedge_seen_p); return 1; } } return 0; } /* We are exiting E->src, see if E->dest ends with a conditional jump which has a known value when reached via E. Special care is necessary if E is a back edge in the CFG as we may have already recorded equivalences for E->dest into our various tables, including the result of the conditional at the end of E->dest. Threading opportunities are severely limited in that case to avoid short-circuiting the loop incorrectly. Note it is quite common for the first block inside a loop to end with a conditional which is either always true or always false when reached via the loop backedge. Thus we do not want to blindly disable threading across a loop backedge. DUMMY_COND is a shared cond_expr used by condition simplification as scratch, to avoid allocating memory. HANDLE_DOMINATING_ASSERTS is true if we should try to replace operands of the simplified condition with left-hand sides of ASSERT_EXPRs they are used in. STACK is used to undo temporary equivalences created during the walk of E->dest. SIMPLIFY is a pass-specific function used to simplify statements. */ void thread_across_edge (gimple dummy_cond, edge e, bool handle_dominating_asserts, vec *stack, tree (*simplify) (gimple, gimple)) { bitmap visited = BITMAP_ALLOC (NULL); bool backedge_seen; stmt_count = 0; vec *path = new vec (); bitmap_clear (visited); bitmap_set_bit (visited, e->src->index); bitmap_set_bit (visited, e->dest->index); backedge_seen = ((e->flags & EDGE_DFS_BACK) != 0); if (backedge_seen) simplify = dummy_simplify; int threaded = thread_through_normal_block (e, dummy_cond, handle_dominating_asserts, stack, simplify, path, visited, &backedge_seen); if (threaded > 0) { propagate_threaded_block_debug_into (path->last ()->e->dest, e->dest); remove_temporary_equivalences (stack); BITMAP_FREE (visited); register_jump_thread (path); return; } else { /* Negative and zero return values indicate no threading was possible, thus there should be no edges on the thread path and no need to walk through the vector entries. */ gcc_assert (path->length () == 0); path->release (); /* A negative status indicates the target block was deemed too big to duplicate. Just quit now rather than trying to use the block as a joiner in a jump threading path. This prevents unnecessary code growth, but more importantly if we do not look at all the statements in the block, then we may have missed some invalidations if we had traversed a backedge! */ if (threaded < 0) { BITMAP_FREE (visited); remove_temporary_equivalences (stack); return; } } /* We were unable to determine what out edge from E->dest is taken. However, we might still be able to thread through successors of E->dest. This often occurs when E->dest is a joiner block which then fans back out based on redundant tests. If so, we'll copy E->dest and redirect the appropriate predecessor to the copy. Within the copy of E->dest, we'll thread one or more edges to points deeper in the CFG. This is a stopgap until we have a more structured approach to path isolation. */ { edge taken_edge; edge_iterator ei; bool found; /* If E->dest has abnormal outgoing edges, then there's no guarantee we can safely redirect any of the edges. Just punt those cases. */ FOR_EACH_EDGE (taken_edge, ei, e->dest->succs) if (taken_edge->flags & EDGE_ABNORMAL) { remove_temporary_equivalences (stack); BITMAP_FREE (visited); return; } /* Look at each successor of E->dest to see if we can thread through it. */ FOR_EACH_EDGE (taken_edge, ei, e->dest->succs) { /* Push a fresh marker so we can unwind the equivalences created for each of E->dest's successors. */ stack->safe_push (NULL_TREE); /* Avoid threading to any block we have already visited. */ bitmap_clear (visited); bitmap_set_bit (visited, e->src->index); bitmap_set_bit (visited, e->dest->index); bitmap_set_bit (visited, taken_edge->dest->index); vec *path = new vec (); /* Record whether or not we were able to thread through a successor of E->dest. */ jump_thread_edge *x = new jump_thread_edge (e, EDGE_START_JUMP_THREAD); path->safe_push (x); x = new jump_thread_edge (taken_edge, EDGE_COPY_SRC_JOINER_BLOCK); path->safe_push (x); found = false; backedge_seen = ((e->flags & EDGE_DFS_BACK) != 0); backedge_seen |= ((taken_edge->flags & EDGE_DFS_BACK) != 0); if (backedge_seen) simplify = dummy_simplify; found = thread_around_empty_blocks (taken_edge, dummy_cond, handle_dominating_asserts, simplify, visited, path, &backedge_seen); if (backedge_seen) simplify = dummy_simplify; if (!found) found = thread_through_normal_block (path->last ()->e, dummy_cond, handle_dominating_asserts, stack, simplify, path, visited, &backedge_seen) > 0; /* If we were able to thread through a successor of E->dest, then record the jump threading opportunity. */ if (found) { propagate_threaded_block_debug_into (path->last ()->e->dest, taken_edge->dest); register_jump_thread (path); } else { delete_jump_thread_path (path); } /* And unwind the equivalence table. */ remove_temporary_equivalences (stack); } BITMAP_FREE (visited); } remove_temporary_equivalences (stack); }