| /* Tail call optimization on trees. |
| Copyright (C) 2003-2020 Free Software Foundation, Inc. |
| |
| This file is part of GCC. |
| |
| GCC is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 3, or (at your option) |
| any later version. |
| |
| GCC is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GCC; see the file COPYING3. If not see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include "config.h" |
| #include "system.h" |
| #include "coretypes.h" |
| #include "backend.h" |
| #include "rtl.h" |
| #include "tree.h" |
| #include "gimple.h" |
| #include "cfghooks.h" |
| #include "tree-pass.h" |
| #include "ssa.h" |
| #include "cgraph.h" |
| #include "gimple-pretty-print.h" |
| #include "fold-const.h" |
| #include "stor-layout.h" |
| #include "gimple-iterator.h" |
| #include "gimplify-me.h" |
| #include "tree-cfg.h" |
| #include "tree-into-ssa.h" |
| #include "tree-dfa.h" |
| #include "except.h" |
| #include "tree-eh.h" |
| #include "dbgcnt.h" |
| #include "cfgloop.h" |
| #include "common/common-target.h" |
| #include "ipa-utils.h" |
| #include "tree-ssa-live.h" |
| |
| /* The file implements the tail recursion elimination. It is also used to |
| analyze the tail calls in general, passing the results to the rtl level |
| where they are used for sibcall optimization. |
| |
| In addition to the standard tail recursion elimination, we handle the most |
| trivial cases of making the call tail recursive by creating accumulators. |
| For example the following function |
| |
| int sum (int n) |
| { |
| if (n > 0) |
| return n + sum (n - 1); |
| else |
| return 0; |
| } |
| |
| is transformed into |
| |
| int sum (int n) |
| { |
| int acc = 0; |
| |
| while (n > 0) |
| acc += n--; |
| |
| return acc; |
| } |
| |
| To do this, we maintain two accumulators (a_acc and m_acc) that indicate |
| when we reach the return x statement, we should return a_acc + x * m_acc |
| instead. They are initially initialized to 0 and 1, respectively, |
| so the semantics of the function is obviously preserved. If we are |
| guaranteed that the value of the accumulator never change, we |
| omit the accumulator. |
| |
| There are three cases how the function may exit. The first one is |
| handled in adjust_return_value, the other two in adjust_accumulator_values |
| (the second case is actually a special case of the third one and we |
| present it separately just for clarity): |
| |
| 1) Just return x, where x is not in any of the remaining special shapes. |
| We rewrite this to a gimple equivalent of return m_acc * x + a_acc. |
| |
| 2) return f (...), where f is the current function, is rewritten in a |
| classical tail-recursion elimination way, into assignment of arguments |
| and jump to the start of the function. Values of the accumulators |
| are unchanged. |
| |
| 3) return a + m * f(...), where a and m do not depend on call to f. |
| To preserve the semantics described before we want this to be rewritten |
| in such a way that we finally return |
| |
| a_acc + (a + m * f(...)) * m_acc = (a_acc + a * m_acc) + (m * m_acc) * f(...). |
| |
| I.e. we increase a_acc by a * m_acc, multiply m_acc by m and |
| eliminate the tail call to f. Special cases when the value is just |
| added or just multiplied are obtained by setting a = 0 or m = 1. |
| |
| TODO -- it is possible to do similar tricks for other operations. */ |
| |
| /* A structure that describes the tailcall. */ |
| |
| struct tailcall |
| { |
| /* The iterator pointing to the call statement. */ |
| gimple_stmt_iterator call_gsi; |
| |
| /* True if it is a call to the current function. */ |
| bool tail_recursion; |
| |
| /* The return value of the caller is mult * f + add, where f is the return |
| value of the call. */ |
| tree mult, add; |
| |
| /* Next tailcall in the chain. */ |
| struct tailcall *next; |
| }; |
| |
| /* The variables holding the value of multiplicative and additive |
| accumulator. */ |
| static tree m_acc, a_acc; |
| |
| /* Bitmap with a bit for each function parameter which is set to true if we |
| have to copy the parameter for conversion of tail-recursive calls. */ |
| |
| static bitmap tailr_arg_needs_copy; |
| |
| static bool optimize_tail_call (struct tailcall *, bool); |
| static void eliminate_tail_call (struct tailcall *); |
| |
| /* Returns false when the function is not suitable for tail call optimization |
| from some reason (e.g. if it takes variable number of arguments). */ |
| |
| static bool |
| suitable_for_tail_opt_p (void) |
| { |
| if (cfun->stdarg) |
| return false; |
| |
| return true; |
| } |
| |
| /* Returns false when the function is not suitable for tail call optimization |
| for some reason (e.g. if it takes variable number of arguments). |
| This test must pass in addition to suitable_for_tail_opt_p in order to make |
| tail call discovery happen. */ |
| |
| static bool |
| suitable_for_tail_call_opt_p (void) |
| { |
| tree param; |
| |
| /* alloca (until we have stack slot life analysis) inhibits |
| sibling call optimizations, but not tail recursion. */ |
| if (cfun->calls_alloca) |
| return false; |
| |
| /* If we are using sjlj exceptions, we may need to add a call to |
| _Unwind_SjLj_Unregister at exit of the function. Which means |
| that we cannot do any sibcall transformations. */ |
| if (targetm_common.except_unwind_info (&global_options) == UI_SJLJ |
| && current_function_has_exception_handlers ()) |
| return false; |
| |
| /* Any function that calls setjmp might have longjmp called from |
| any called function. ??? We really should represent this |
| properly in the CFG so that this needn't be special cased. */ |
| if (cfun->calls_setjmp) |
| return false; |
| |
| /* Various targets don't handle tail calls correctly in functions |
| that call __builtin_eh_return. */ |
| if (cfun->calls_eh_return) |
| return false; |
| |
| /* ??? It is OK if the argument of a function is taken in some cases, |
| but not in all cases. See PR15387 and PR19616. Revisit for 4.1. */ |
| for (param = DECL_ARGUMENTS (current_function_decl); |
| param; |
| param = DECL_CHAIN (param)) |
| if (TREE_ADDRESSABLE (param)) |
| return false; |
| |
| return true; |
| } |
| |
| /* Checks whether the expression EXPR in stmt AT is independent of the |
| statement pointed to by GSI (in a sense that we already know EXPR's value |
| at GSI). We use the fact that we are only called from the chain of |
| basic blocks that have only single successor. Returns the expression |
| containing the value of EXPR at GSI. */ |
| |
| static tree |
| independent_of_stmt_p (tree expr, gimple *at, gimple_stmt_iterator gsi, |
| bitmap to_move) |
| { |
| basic_block bb, call_bb, at_bb; |
| edge e; |
| edge_iterator ei; |
| |
| if (is_gimple_min_invariant (expr)) |
| return expr; |
| |
| if (TREE_CODE (expr) != SSA_NAME) |
| return NULL_TREE; |
| |
| if (bitmap_bit_p (to_move, SSA_NAME_VERSION (expr))) |
| return expr; |
| |
| /* Mark the blocks in the chain leading to the end. */ |
| at_bb = gimple_bb (at); |
| call_bb = gimple_bb (gsi_stmt (gsi)); |
| for (bb = call_bb; bb != at_bb; bb = single_succ (bb)) |
| bb->aux = &bb->aux; |
| bb->aux = &bb->aux; |
| |
| while (1) |
| { |
| at = SSA_NAME_DEF_STMT (expr); |
| bb = gimple_bb (at); |
| |
| /* The default definition or defined before the chain. */ |
| if (!bb || !bb->aux) |
| break; |
| |
| if (bb == call_bb) |
| { |
| for (; !gsi_end_p (gsi); gsi_next (&gsi)) |
| if (gsi_stmt (gsi) == at) |
| break; |
| |
| if (!gsi_end_p (gsi)) |
| expr = NULL_TREE; |
| break; |
| } |
| |
| if (gimple_code (at) != GIMPLE_PHI) |
| { |
| expr = NULL_TREE; |
| break; |
| } |
| |
| FOR_EACH_EDGE (e, ei, bb->preds) |
| if (e->src->aux) |
| break; |
| gcc_assert (e); |
| |
| expr = PHI_ARG_DEF_FROM_EDGE (at, e); |
| if (TREE_CODE (expr) != SSA_NAME) |
| { |
| /* The value is a constant. */ |
| break; |
| } |
| } |
| |
| /* Unmark the blocks. */ |
| for (bb = call_bb; bb != at_bb; bb = single_succ (bb)) |
| bb->aux = NULL; |
| bb->aux = NULL; |
| |
| return expr; |
| } |
| |
| enum par { FAIL, OK, TRY_MOVE }; |
| |
| /* Simulates the effect of an assignment STMT on the return value of the tail |
| recursive CALL passed in ASS_VAR. M and A are the multiplicative and the |
| additive factor for the real return value. */ |
| |
| static par |
| process_assignment (gassign *stmt, |
| gimple_stmt_iterator call, tree *m, |
| tree *a, tree *ass_var, bitmap to_move) |
| { |
| tree op0, op1 = NULL_TREE, non_ass_var = NULL_TREE; |
| tree dest = gimple_assign_lhs (stmt); |
| enum tree_code code = gimple_assign_rhs_code (stmt); |
| enum gimple_rhs_class rhs_class = get_gimple_rhs_class (code); |
| tree src_var = gimple_assign_rhs1 (stmt); |
| |
| /* See if this is a simple copy operation of an SSA name to the function |
| result. In that case we may have a simple tail call. Ignore type |
| conversions that can never produce extra code between the function |
| call and the function return. */ |
| if ((rhs_class == GIMPLE_SINGLE_RHS || gimple_assign_cast_p (stmt)) |
| && src_var == *ass_var) |
| { |
| /* Reject a tailcall if the type conversion might need |
| additional code. */ |
| if (gimple_assign_cast_p (stmt)) |
| { |
| if (TYPE_MODE (TREE_TYPE (dest)) != TYPE_MODE (TREE_TYPE (src_var))) |
| return FAIL; |
| |
| /* Even if the type modes are the same, if the precision of the |
| type is smaller than mode's precision, |
| reduce_to_bit_field_precision would generate additional code. */ |
| if (INTEGRAL_TYPE_P (TREE_TYPE (dest)) |
| && !type_has_mode_precision_p (TREE_TYPE (dest))) |
| return FAIL; |
| } |
| |
| *ass_var = dest; |
| return OK; |
| } |
| |
| switch (rhs_class) |
| { |
| case GIMPLE_BINARY_RHS: |
| op1 = gimple_assign_rhs2 (stmt); |
| |
| /* Fall through. */ |
| |
| case GIMPLE_UNARY_RHS: |
| op0 = gimple_assign_rhs1 (stmt); |
| break; |
| |
| default: |
| return FAIL; |
| } |
| |
| /* Accumulator optimizations will reverse the order of operations. |
| We can only do that for floating-point types if we're assuming |
| that addition and multiplication are associative. */ |
| if (!flag_associative_math) |
| if (FLOAT_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl)))) |
| return FAIL; |
| |
| if (rhs_class == GIMPLE_UNARY_RHS |
| && op0 == *ass_var) |
| ; |
| else if (op0 == *ass_var |
| && (non_ass_var = independent_of_stmt_p (op1, stmt, call, |
| to_move))) |
| ; |
| else if (*ass_var |
| && op1 == *ass_var |
| && (non_ass_var = independent_of_stmt_p (op0, stmt, call, |
| to_move))) |
| ; |
| else |
| return TRY_MOVE; |
| |
| switch (code) |
| { |
| case PLUS_EXPR: |
| *a = non_ass_var; |
| *ass_var = dest; |
| return OK; |
| |
| case POINTER_PLUS_EXPR: |
| if (op0 != *ass_var) |
| return FAIL; |
| *a = non_ass_var; |
| *ass_var = dest; |
| return OK; |
| |
| case MULT_EXPR: |
| *m = non_ass_var; |
| *ass_var = dest; |
| return OK; |
| |
| case NEGATE_EXPR: |
| *m = build_minus_one_cst (TREE_TYPE (op0)); |
| *ass_var = dest; |
| return OK; |
| |
| case MINUS_EXPR: |
| if (*ass_var == op0) |
| *a = fold_build1 (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var); |
| else |
| { |
| *m = build_minus_one_cst (TREE_TYPE (non_ass_var)); |
| *a = fold_build1 (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var); |
| } |
| |
| *ass_var = dest; |
| return OK; |
| |
| default: |
| return FAIL; |
| } |
| } |
| |
| /* Propagate VAR through phis on edge E. */ |
| |
| static tree |
| propagate_through_phis (tree var, edge e) |
| { |
| basic_block dest = e->dest; |
| gphi_iterator gsi; |
| |
| for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi)) |
| { |
| gphi *phi = gsi.phi (); |
| if (PHI_ARG_DEF_FROM_EDGE (phi, e) == var) |
| return PHI_RESULT (phi); |
| } |
| return var; |
| } |
| |
| /* Argument for compute_live_vars/live_vars_at_stmt and what compute_live_vars |
| returns. Computed lazily, but just once for the function. */ |
| static live_vars_map *live_vars; |
| static vec<bitmap_head> live_vars_vec; |
| |
| /* Finds tailcalls falling into basic block BB. The list of found tailcalls is |
| added to the start of RET. */ |
| |
| static void |
| find_tail_calls (basic_block bb, struct tailcall **ret) |
| { |
| tree ass_var = NULL_TREE, ret_var, func, param; |
| gimple *stmt; |
| gcall *call = NULL; |
| gimple_stmt_iterator gsi, agsi; |
| bool tail_recursion; |
| struct tailcall *nw; |
| edge e; |
| tree m, a; |
| basic_block abb; |
| size_t idx; |
| tree var; |
| |
| if (!single_succ_p (bb)) |
| return; |
| |
| for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi)) |
| { |
| stmt = gsi_stmt (gsi); |
| |
| /* Ignore labels, returns, nops, clobbers and debug stmts. */ |
| if (gimple_code (stmt) == GIMPLE_LABEL |
| || gimple_code (stmt) == GIMPLE_RETURN |
| || gimple_code (stmt) == GIMPLE_NOP |
| || gimple_code (stmt) == GIMPLE_PREDICT |
| || gimple_clobber_p (stmt) |
| || is_gimple_debug (stmt)) |
| continue; |
| |
| /* Check for a call. */ |
| if (is_gimple_call (stmt)) |
| { |
| call = as_a <gcall *> (stmt); |
| ass_var = gimple_call_lhs (call); |
| break; |
| } |
| |
| /* Allow simple copies between local variables, even if they're |
| aggregates. */ |
| if (is_gimple_assign (stmt) |
| && auto_var_in_fn_p (gimple_assign_lhs (stmt), cfun->decl) |
| && auto_var_in_fn_p (gimple_assign_rhs1 (stmt), cfun->decl)) |
| continue; |
| |
| /* If the statement references memory or volatile operands, fail. */ |
| if (gimple_references_memory_p (stmt) |
| || gimple_has_volatile_ops (stmt)) |
| return; |
| } |
| |
| if (gsi_end_p (gsi)) |
| { |
| edge_iterator ei; |
| /* Recurse to the predecessors. */ |
| FOR_EACH_EDGE (e, ei, bb->preds) |
| find_tail_calls (e->src, ret); |
| |
| return; |
| } |
| |
| /* If the LHS of our call is not just a simple register or local |
| variable, we can't transform this into a tail or sibling call. |
| This situation happens, in (e.g.) "*p = foo()" where foo returns a |
| struct. In this case we won't have a temporary here, but we need |
| to carry out the side effect anyway, so tailcall is impossible. |
| |
| ??? In some situations (when the struct is returned in memory via |
| invisible argument) we could deal with this, e.g. by passing 'p' |
| itself as that argument to foo, but it's too early to do this here, |
| and expand_call() will not handle it anyway. If it ever can, then |
| we need to revisit this here, to allow that situation. */ |
| if (ass_var |
| && !is_gimple_reg (ass_var) |
| && !auto_var_in_fn_p (ass_var, cfun->decl)) |
| return; |
| |
| /* If the call might throw an exception that wouldn't propagate out of |
| cfun, we can't transform to a tail or sibling call (82081). */ |
| if (stmt_could_throw_p (cfun, stmt) |
| && !stmt_can_throw_external (cfun, stmt)) |
| return; |
| |
| /* If the function returns a value, then at present, the tail call |
| must return the same type of value. There is conceptually a copy |
| between the object returned by the tail call candidate and the |
| object returned by CFUN itself. |
| |
| This means that if we have: |
| |
| lhs = f (&<retval>); // f reads from <retval> |
| // (lhs is usually also <retval>) |
| |
| there is a copy between the temporary object returned by f and lhs, |
| meaning that any use of <retval> in f occurs before the assignment |
| to lhs begins. Thus the <retval> that is live on entry to the call |
| to f is really an independent local variable V that happens to be |
| stored in the RESULT_DECL rather than a local VAR_DECL. |
| |
| Turning this into a tail call would remove the copy and make the |
| lifetimes of the return value and V overlap. The same applies to |
| tail recursion, since if f can read from <retval>, we have to assume |
| that CFUN might already have written to <retval> before the call. |
| |
| The problem doesn't apply when <retval> is passed by value, but that |
| isn't a case we handle anyway. */ |
| tree result_decl = DECL_RESULT (cfun->decl); |
| if (result_decl |
| && may_be_aliased (result_decl) |
| && ref_maybe_used_by_stmt_p (call, result_decl)) |
| return; |
| |
| /* We found the call, check whether it is suitable. */ |
| tail_recursion = false; |
| func = gimple_call_fndecl (call); |
| if (func |
| && !fndecl_built_in_p (func) |
| && recursive_call_p (current_function_decl, func)) |
| { |
| tree arg; |
| |
| for (param = DECL_ARGUMENTS (current_function_decl), idx = 0; |
| param && idx < gimple_call_num_args (call); |
| param = DECL_CHAIN (param), idx ++) |
| { |
| arg = gimple_call_arg (call, idx); |
| if (param != arg) |
| { |
| /* Make sure there are no problems with copying. The parameter |
| have a copyable type and the two arguments must have reasonably |
| equivalent types. The latter requirement could be relaxed if |
| we emitted a suitable type conversion statement. */ |
| if (!is_gimple_reg_type (TREE_TYPE (param)) |
| || !useless_type_conversion_p (TREE_TYPE (param), |
| TREE_TYPE (arg))) |
| break; |
| |
| /* The parameter should be a real operand, so that phi node |
| created for it at the start of the function has the meaning |
| of copying the value. This test implies is_gimple_reg_type |
| from the previous condition, however this one could be |
| relaxed by being more careful with copying the new value |
| of the parameter (emitting appropriate GIMPLE_ASSIGN and |
| updating the virtual operands). */ |
| if (!is_gimple_reg (param)) |
| break; |
| } |
| } |
| if (idx == gimple_call_num_args (call) && !param) |
| tail_recursion = true; |
| } |
| |
| /* Compute live vars if not computed yet. */ |
| if (live_vars == NULL) |
| { |
| unsigned int cnt = 0; |
| FOR_EACH_LOCAL_DECL (cfun, idx, var) |
| if (VAR_P (var) |
| && auto_var_in_fn_p (var, cfun->decl) |
| && may_be_aliased (var)) |
| { |
| if (live_vars == NULL) |
| live_vars = new live_vars_map; |
| live_vars->put (DECL_UID (var), cnt++); |
| } |
| if (live_vars) |
| live_vars_vec = compute_live_vars (cfun, live_vars); |
| } |
| |
| /* Determine a bitmap of variables which are still in scope after the |
| call. */ |
| bitmap local_live_vars = NULL; |
| if (live_vars) |
| local_live_vars = live_vars_at_stmt (live_vars_vec, live_vars, call); |
| |
| /* Make sure the tail invocation of this function does not indirectly |
| refer to local variables. (Passing variables directly by value |
| is OK.) */ |
| FOR_EACH_LOCAL_DECL (cfun, idx, var) |
| { |
| if (TREE_CODE (var) != PARM_DECL |
| && auto_var_in_fn_p (var, cfun->decl) |
| && may_be_aliased (var) |
| && (ref_maybe_used_by_stmt_p (call, var) |
| || call_may_clobber_ref_p (call, var))) |
| { |
| if (!VAR_P (var)) |
| { |
| if (local_live_vars) |
| BITMAP_FREE (local_live_vars); |
| return; |
| } |
| else |
| { |
| unsigned int *v = live_vars->get (DECL_UID (var)); |
| if (bitmap_bit_p (local_live_vars, *v)) |
| { |
| BITMAP_FREE (local_live_vars); |
| return; |
| } |
| } |
| } |
| } |
| |
| if (local_live_vars) |
| BITMAP_FREE (local_live_vars); |
| |
| /* Now check the statements after the call. None of them has virtual |
| operands, so they may only depend on the call through its return |
| value. The return value should also be dependent on each of them, |
| since we are running after dce. */ |
| m = NULL_TREE; |
| a = NULL_TREE; |
| auto_bitmap to_move_defs; |
| auto_vec<gimple *> to_move_stmts; |
| |
| abb = bb; |
| agsi = gsi; |
| while (1) |
| { |
| tree tmp_a = NULL_TREE; |
| tree tmp_m = NULL_TREE; |
| gsi_next (&agsi); |
| |
| while (gsi_end_p (agsi)) |
| { |
| ass_var = propagate_through_phis (ass_var, single_succ_edge (abb)); |
| abb = single_succ (abb); |
| agsi = gsi_start_bb (abb); |
| } |
| |
| stmt = gsi_stmt (agsi); |
| if (gimple_code (stmt) == GIMPLE_RETURN) |
| break; |
| |
| if (gimple_code (stmt) == GIMPLE_LABEL |
| || gimple_code (stmt) == GIMPLE_NOP |
| || gimple_code (stmt) == GIMPLE_PREDICT |
| || gimple_clobber_p (stmt) |
| || is_gimple_debug (stmt)) |
| continue; |
| |
| if (gimple_code (stmt) != GIMPLE_ASSIGN) |
| return; |
| |
| /* This is a gimple assign. */ |
| par ret = process_assignment (as_a <gassign *> (stmt), gsi, |
| &tmp_m, &tmp_a, &ass_var, to_move_defs); |
| if (ret == FAIL) |
| return; |
| else if (ret == TRY_MOVE) |
| { |
| if (! tail_recursion) |
| return; |
| /* Do not deal with checking dominance, the real fix is to |
| do path isolation for the transform phase anyway, removing |
| the need to compute the accumulators with new stmts. */ |
| if (abb != bb) |
| return; |
| for (unsigned opno = 1; opno < gimple_num_ops (stmt); ++opno) |
| { |
| tree op = gimple_op (stmt, opno); |
| if (independent_of_stmt_p (op, stmt, gsi, to_move_defs) != op) |
| return; |
| } |
| bitmap_set_bit (to_move_defs, |
| SSA_NAME_VERSION (gimple_assign_lhs (stmt))); |
| to_move_stmts.safe_push (stmt); |
| continue; |
| } |
| |
| if (tmp_a) |
| { |
| tree type = TREE_TYPE (tmp_a); |
| if (a) |
| a = fold_build2 (PLUS_EXPR, type, fold_convert (type, a), tmp_a); |
| else |
| a = tmp_a; |
| } |
| if (tmp_m) |
| { |
| tree type = TREE_TYPE (tmp_m); |
| if (m) |
| m = fold_build2 (MULT_EXPR, type, fold_convert (type, m), tmp_m); |
| else |
| m = tmp_m; |
| |
| if (a) |
| a = fold_build2 (MULT_EXPR, type, fold_convert (type, a), tmp_m); |
| } |
| } |
| |
| /* See if this is a tail call we can handle. */ |
| ret_var = gimple_return_retval (as_a <greturn *> (stmt)); |
| |
| /* We may proceed if there either is no return value, or the return value |
| is identical to the call's return. */ |
| if (ret_var |
| && (ret_var != ass_var)) |
| return; |
| |
| /* If this is not a tail recursive call, we cannot handle addends or |
| multiplicands. */ |
| if (!tail_recursion && (m || a)) |
| return; |
| |
| /* For pointers only allow additions. */ |
| if (m && POINTER_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl)))) |
| return; |
| |
| /* Move queued defs. */ |
| if (tail_recursion) |
| { |
| unsigned i; |
| FOR_EACH_VEC_ELT (to_move_stmts, i, stmt) |
| { |
| gimple_stmt_iterator mgsi = gsi_for_stmt (stmt); |
| gsi_move_before (&mgsi, &gsi); |
| } |
| if (!tailr_arg_needs_copy) |
| tailr_arg_needs_copy = BITMAP_ALLOC (NULL); |
| for (param = DECL_ARGUMENTS (current_function_decl), idx = 0; |
| param; |
| param = DECL_CHAIN (param), idx++) |
| { |
| tree ddef, arg = gimple_call_arg (call, idx); |
| if (is_gimple_reg (param) |
| && (ddef = ssa_default_def (cfun, param)) |
| && (arg != ddef)) |
| bitmap_set_bit (tailr_arg_needs_copy, idx); |
| } |
| } |
| |
| nw = XNEW (struct tailcall); |
| |
| nw->call_gsi = gsi; |
| |
| nw->tail_recursion = tail_recursion; |
| |
| nw->mult = m; |
| nw->add = a; |
| |
| nw->next = *ret; |
| *ret = nw; |
| } |
| |
| /* Helper to insert PHI_ARGH to the phi of VAR in the destination of edge E. */ |
| |
| static void |
| add_successor_phi_arg (edge e, tree var, tree phi_arg) |
| { |
| gphi_iterator gsi; |
| |
| for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) |
| if (PHI_RESULT (gsi.phi ()) == var) |
| break; |
| |
| gcc_assert (!gsi_end_p (gsi)); |
| add_phi_arg (gsi.phi (), phi_arg, e, UNKNOWN_LOCATION); |
| } |
| |
| /* Creates a GIMPLE statement which computes the operation specified by |
| CODE, ACC and OP1 to a new variable with name LABEL and inserts the |
| statement in the position specified by GSI. Returns the |
| tree node of the statement's result. */ |
| |
| static tree |
| adjust_return_value_with_ops (enum tree_code code, const char *label, |
| tree acc, tree op1, gimple_stmt_iterator gsi) |
| { |
| |
| tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); |
| tree result = make_temp_ssa_name (ret_type, NULL, label); |
| gassign *stmt; |
| |
| if (POINTER_TYPE_P (ret_type)) |
| { |
| gcc_assert (code == PLUS_EXPR && TREE_TYPE (acc) == sizetype); |
| code = POINTER_PLUS_EXPR; |
| } |
| if (types_compatible_p (TREE_TYPE (acc), TREE_TYPE (op1)) |
| && code != POINTER_PLUS_EXPR) |
| stmt = gimple_build_assign (result, code, acc, op1); |
| else |
| { |
| tree tem; |
| if (code == POINTER_PLUS_EXPR) |
| tem = fold_build2 (code, TREE_TYPE (op1), op1, acc); |
| else |
| tem = fold_build2 (code, TREE_TYPE (op1), |
| fold_convert (TREE_TYPE (op1), acc), op1); |
| tree rhs = fold_convert (ret_type, tem); |
| rhs = force_gimple_operand_gsi (&gsi, rhs, |
| false, NULL, true, GSI_SAME_STMT); |
| stmt = gimple_build_assign (result, rhs); |
| } |
| |
| gsi_insert_before (&gsi, stmt, GSI_NEW_STMT); |
| return result; |
| } |
| |
| /* Creates a new GIMPLE statement that adjusts the value of accumulator ACC by |
| the computation specified by CODE and OP1 and insert the statement |
| at the position specified by GSI as a new statement. Returns new SSA name |
| of updated accumulator. */ |
| |
| static tree |
| update_accumulator_with_ops (enum tree_code code, tree acc, tree op1, |
| gimple_stmt_iterator gsi) |
| { |
| gassign *stmt; |
| tree var = copy_ssa_name (acc); |
| if (types_compatible_p (TREE_TYPE (acc), TREE_TYPE (op1))) |
| stmt = gimple_build_assign (var, code, acc, op1); |
| else |
| { |
| tree rhs = fold_convert (TREE_TYPE (acc), |
| fold_build2 (code, |
| TREE_TYPE (op1), |
| fold_convert (TREE_TYPE (op1), acc), |
| op1)); |
| rhs = force_gimple_operand_gsi (&gsi, rhs, |
| false, NULL, false, GSI_CONTINUE_LINKING); |
| stmt = gimple_build_assign (var, rhs); |
| } |
| gsi_insert_after (&gsi, stmt, GSI_NEW_STMT); |
| return var; |
| } |
| |
| /* Adjust the accumulator values according to A and M after GSI, and update |
| the phi nodes on edge BACK. */ |
| |
| static void |
| adjust_accumulator_values (gimple_stmt_iterator gsi, tree m, tree a, edge back) |
| { |
| tree var, a_acc_arg, m_acc_arg; |
| |
| if (m) |
| m = force_gimple_operand_gsi (&gsi, m, true, NULL, true, GSI_SAME_STMT); |
| if (a) |
| a = force_gimple_operand_gsi (&gsi, a, true, NULL, true, GSI_SAME_STMT); |
| |
| a_acc_arg = a_acc; |
| m_acc_arg = m_acc; |
| if (a) |
| { |
| if (m_acc) |
| { |
| if (integer_onep (a)) |
| var = m_acc; |
| else |
| var = adjust_return_value_with_ops (MULT_EXPR, "acc_tmp", m_acc, |
| a, gsi); |
| } |
| else |
| var = a; |
| |
| a_acc_arg = update_accumulator_with_ops (PLUS_EXPR, a_acc, var, gsi); |
| } |
| |
| if (m) |
| m_acc_arg = update_accumulator_with_ops (MULT_EXPR, m_acc, m, gsi); |
| |
| if (a_acc) |
| add_successor_phi_arg (back, a_acc, a_acc_arg); |
| |
| if (m_acc) |
| add_successor_phi_arg (back, m_acc, m_acc_arg); |
| } |
| |
| /* Adjust value of the return at the end of BB according to M and A |
| accumulators. */ |
| |
| static void |
| adjust_return_value (basic_block bb, tree m, tree a) |
| { |
| tree retval; |
| greturn *ret_stmt = as_a <greturn *> (gimple_seq_last_stmt (bb_seq (bb))); |
| gimple_stmt_iterator gsi = gsi_last_bb (bb); |
| |
| gcc_assert (gimple_code (ret_stmt) == GIMPLE_RETURN); |
| |
| retval = gimple_return_retval (ret_stmt); |
| if (!retval || retval == error_mark_node) |
| return; |
| |
| if (m) |
| retval = adjust_return_value_with_ops (MULT_EXPR, "mul_tmp", m_acc, retval, |
| gsi); |
| if (a) |
| retval = adjust_return_value_with_ops (PLUS_EXPR, "acc_tmp", a_acc, retval, |
| gsi); |
| gimple_return_set_retval (ret_stmt, retval); |
| update_stmt (ret_stmt); |
| } |
| |
| /* Subtract COUNT and FREQUENCY from the basic block and it's |
| outgoing edge. */ |
| static void |
| decrease_profile (basic_block bb, profile_count count) |
| { |
| bb->count = bb->count - count; |
| if (!single_succ_p (bb)) |
| { |
| gcc_assert (!EDGE_COUNT (bb->succs)); |
| return; |
| } |
| } |
| |
| /* Eliminates tail call described by T. TMP_VARS is a list of |
| temporary variables used to copy the function arguments. */ |
| |
| static void |
| eliminate_tail_call (struct tailcall *t) |
| { |
| tree param, rslt; |
| gimple *stmt, *call; |
| tree arg; |
| size_t idx; |
| basic_block bb, first; |
| edge e; |
| gphi *phi; |
| gphi_iterator gpi; |
| gimple_stmt_iterator gsi; |
| gimple *orig_stmt; |
| |
| stmt = orig_stmt = gsi_stmt (t->call_gsi); |
| bb = gsi_bb (t->call_gsi); |
| |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "Eliminated tail recursion in bb %d : ", |
| bb->index); |
| print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); |
| fprintf (dump_file, "\n"); |
| } |
| |
| gcc_assert (is_gimple_call (stmt)); |
| |
| first = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)); |
| |
| /* Remove the code after call_gsi that will become unreachable. The |
| possibly unreachable code in other blocks is removed later in |
| cfg cleanup. */ |
| gsi = t->call_gsi; |
| gimple_stmt_iterator gsi2 = gsi_last_bb (gimple_bb (gsi_stmt (gsi))); |
| while (gsi_stmt (gsi2) != gsi_stmt (gsi)) |
| { |
| gimple *t = gsi_stmt (gsi2); |
| /* Do not remove the return statement, so that redirect_edge_and_branch |
| sees how the block ends. */ |
| if (gimple_code (t) != GIMPLE_RETURN) |
| { |
| gimple_stmt_iterator gsi3 = gsi2; |
| gsi_prev (&gsi2); |
| gsi_remove (&gsi3, true); |
| release_defs (t); |
| } |
| else |
| gsi_prev (&gsi2); |
| } |
| |
| /* Number of executions of function has reduced by the tailcall. */ |
| e = single_succ_edge (gsi_bb (t->call_gsi)); |
| |
| profile_count count = e->count (); |
| |
| /* When profile is inconsistent and the recursion edge is more frequent |
| than number of executions of functions, scale it down, so we do not end |
| up with 0 executions of entry block. */ |
| if (count >= ENTRY_BLOCK_PTR_FOR_FN (cfun)->count) |
| count = ENTRY_BLOCK_PTR_FOR_FN (cfun)->count.apply_scale (7, 8); |
| decrease_profile (EXIT_BLOCK_PTR_FOR_FN (cfun), count); |
| decrease_profile (ENTRY_BLOCK_PTR_FOR_FN (cfun), count); |
| if (e->dest != EXIT_BLOCK_PTR_FOR_FN (cfun)) |
| decrease_profile (e->dest, count); |
| |
| /* Replace the call by a jump to the start of function. */ |
| e = redirect_edge_and_branch (single_succ_edge (gsi_bb (t->call_gsi)), |
| first); |
| gcc_assert (e); |
| PENDING_STMT (e) = NULL; |
| |
| /* Add phi node entries for arguments. The ordering of the phi nodes should |
| be the same as the ordering of the arguments. */ |
| for (param = DECL_ARGUMENTS (current_function_decl), |
| idx = 0, gpi = gsi_start_phis (first); |
| param; |
| param = DECL_CHAIN (param), idx++) |
| { |
| if (!bitmap_bit_p (tailr_arg_needs_copy, idx)) |
| continue; |
| |
| arg = gimple_call_arg (stmt, idx); |
| phi = gpi.phi (); |
| gcc_assert (param == SSA_NAME_VAR (PHI_RESULT (phi))); |
| |
| add_phi_arg (phi, arg, e, gimple_location (stmt)); |
| gsi_next (&gpi); |
| } |
| |
| /* Update the values of accumulators. */ |
| adjust_accumulator_values (t->call_gsi, t->mult, t->add, e); |
| |
| call = gsi_stmt (t->call_gsi); |
| rslt = gimple_call_lhs (call); |
| if (rslt != NULL_TREE && TREE_CODE (rslt) == SSA_NAME) |
| { |
| /* Result of the call will no longer be defined. So adjust the |
| SSA_NAME_DEF_STMT accordingly. */ |
| SSA_NAME_DEF_STMT (rslt) = gimple_build_nop (); |
| } |
| |
| gsi_remove (&t->call_gsi, true); |
| release_defs (call); |
| } |
| |
| /* Optimizes the tailcall described by T. If OPT_TAILCALLS is true, also |
| mark the tailcalls for the sibcall optimization. */ |
| |
| static bool |
| optimize_tail_call (struct tailcall *t, bool opt_tailcalls) |
| { |
| if (t->tail_recursion) |
| { |
| eliminate_tail_call (t); |
| return true; |
| } |
| |
| if (opt_tailcalls) |
| { |
| gcall *stmt = as_a <gcall *> (gsi_stmt (t->call_gsi)); |
| |
| gimple_call_set_tail (stmt, true); |
| cfun->tail_call_marked = true; |
| if (dump_file && (dump_flags & TDF_DETAILS)) |
| { |
| fprintf (dump_file, "Found tail call "); |
| print_gimple_stmt (dump_file, stmt, 0, dump_flags); |
| fprintf (dump_file, " in bb %i\n", (gsi_bb (t->call_gsi))->index); |
| } |
| } |
| |
| return false; |
| } |
| |
| /* Creates a tail-call accumulator of the same type as the return type of the |
| current function. LABEL is the name used to creating the temporary |
| variable for the accumulator. The accumulator will be inserted in the |
| phis of a basic block BB with single predecessor with an initial value |
| INIT converted to the current function return type. */ |
| |
| static tree |
| create_tailcall_accumulator (const char *label, basic_block bb, tree init) |
| { |
| tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl)); |
| if (POINTER_TYPE_P (ret_type)) |
| ret_type = sizetype; |
| |
| tree tmp = make_temp_ssa_name (ret_type, NULL, label); |
| gphi *phi; |
| |
| phi = create_phi_node (tmp, bb); |
| /* RET_TYPE can be a float when -ffast-maths is enabled. */ |
| add_phi_arg (phi, fold_convert (ret_type, init), single_pred_edge (bb), |
| UNKNOWN_LOCATION); |
| return PHI_RESULT (phi); |
| } |
| |
| /* Optimizes tail calls in the function, turning the tail recursion |
| into iteration. */ |
| |
| static unsigned int |
| tree_optimize_tail_calls_1 (bool opt_tailcalls) |
| { |
| edge e; |
| bool phis_constructed = false; |
| struct tailcall *tailcalls = NULL, *act, *next; |
| bool changed = false; |
| basic_block first = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)); |
| tree param; |
| gimple *stmt; |
| edge_iterator ei; |
| |
| if (!suitable_for_tail_opt_p ()) |
| return 0; |
| if (opt_tailcalls) |
| opt_tailcalls = suitable_for_tail_call_opt_p (); |
| |
| FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (cfun)->preds) |
| { |
| /* Only traverse the normal exits, i.e. those that end with return |
| statement. */ |
| stmt = last_stmt (e->src); |
| |
| if (stmt |
| && gimple_code (stmt) == GIMPLE_RETURN) |
| find_tail_calls (e->src, &tailcalls); |
| } |
| |
| if (live_vars) |
| { |
| destroy_live_vars (live_vars_vec); |
| delete live_vars; |
| live_vars = NULL; |
| } |
| |
| /* Construct the phi nodes and accumulators if necessary. */ |
| a_acc = m_acc = NULL_TREE; |
| for (act = tailcalls; act; act = act->next) |
| { |
| if (!act->tail_recursion) |
| continue; |
| |
| if (!phis_constructed) |
| { |
| /* Ensure that there is only one predecessor of the block |
| or if there are existing degenerate PHI nodes. */ |
| if (!single_pred_p (first) |
| || !gimple_seq_empty_p (phi_nodes (first))) |
| first = |
| split_edge (single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun))); |
| |
| /* Copy the args if needed. */ |
| unsigned idx; |
| for (param = DECL_ARGUMENTS (current_function_decl), idx = 0; |
| param; |
| param = DECL_CHAIN (param), idx++) |
| if (bitmap_bit_p (tailr_arg_needs_copy, idx)) |
| { |
| tree name = ssa_default_def (cfun, param); |
| tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name)); |
| gphi *phi; |
| |
| set_ssa_default_def (cfun, param, new_name); |
| phi = create_phi_node (name, first); |
| add_phi_arg (phi, new_name, single_pred_edge (first), |
| EXPR_LOCATION (param)); |
| } |
| phis_constructed = true; |
| } |
| |
| if (act->add && !a_acc) |
| a_acc = create_tailcall_accumulator ("add_acc", first, |
| integer_zero_node); |
| |
| if (act->mult && !m_acc) |
| m_acc = create_tailcall_accumulator ("mult_acc", first, |
| integer_one_node); |
| } |
| |
| if (a_acc || m_acc) |
| { |
| /* When the tail call elimination using accumulators is performed, |
| statements adding the accumulated value are inserted at all exits. |
| This turns all other tail calls to non-tail ones. */ |
| opt_tailcalls = false; |
| } |
| |
| for (; tailcalls; tailcalls = next) |
| { |
| next = tailcalls->next; |
| changed |= optimize_tail_call (tailcalls, opt_tailcalls); |
| free (tailcalls); |
| } |
| |
| if (a_acc || m_acc) |
| { |
| /* Modify the remaining return statements. */ |
| FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (cfun)->preds) |
| { |
| stmt = last_stmt (e->src); |
| |
| if (stmt |
| && gimple_code (stmt) == GIMPLE_RETURN) |
| adjust_return_value (e->src, m_acc, a_acc); |
| } |
| } |
| |
| if (changed) |
| { |
| /* We may have created new loops. Make them magically appear. */ |
| loops_state_set (LOOPS_NEED_FIXUP); |
| free_dominance_info (CDI_DOMINATORS); |
| } |
| |
| /* Add phi nodes for the virtual operands defined in the function to the |
| header of the loop created by tail recursion elimination. Do so |
| by triggering the SSA renamer. */ |
| if (phis_constructed) |
| mark_virtual_operands_for_renaming (cfun); |
| |
| if (tailr_arg_needs_copy) |
| BITMAP_FREE (tailr_arg_needs_copy); |
| |
| if (changed) |
| return TODO_cleanup_cfg | TODO_update_ssa_only_virtuals; |
| return 0; |
| } |
| |
| static bool |
| gate_tail_calls (void) |
| { |
| return flag_optimize_sibling_calls != 0 && dbg_cnt (tail_call); |
| } |
| |
| static unsigned int |
| execute_tail_calls (void) |
| { |
| return tree_optimize_tail_calls_1 (true); |
| } |
| |
| namespace { |
| |
| const pass_data pass_data_tail_recursion = |
| { |
| GIMPLE_PASS, /* type */ |
| "tailr", /* name */ |
| OPTGROUP_NONE, /* optinfo_flags */ |
| TV_NONE, /* tv_id */ |
| ( PROP_cfg | PROP_ssa ), /* properties_required */ |
| 0, /* properties_provided */ |
| 0, /* properties_destroyed */ |
| 0, /* todo_flags_start */ |
| 0, /* todo_flags_finish */ |
| }; |
| |
| class pass_tail_recursion : public gimple_opt_pass |
| { |
| public: |
| pass_tail_recursion (gcc::context *ctxt) |
| : gimple_opt_pass (pass_data_tail_recursion, ctxt) |
| {} |
| |
| /* opt_pass methods: */ |
| opt_pass * clone () { return new pass_tail_recursion (m_ctxt); } |
| virtual bool gate (function *) { return gate_tail_calls (); } |
| virtual unsigned int execute (function *) |
| { |
| return tree_optimize_tail_calls_1 (false); |
| } |
| |
| }; // class pass_tail_recursion |
| |
| } // anon namespace |
| |
| gimple_opt_pass * |
| make_pass_tail_recursion (gcc::context *ctxt) |
| { |
| return new pass_tail_recursion (ctxt); |
| } |
| |
| namespace { |
| |
| const pass_data pass_data_tail_calls = |
| { |
| GIMPLE_PASS, /* type */ |
| "tailc", /* name */ |
| OPTGROUP_NONE, /* optinfo_flags */ |
| TV_NONE, /* tv_id */ |
| ( PROP_cfg | PROP_ssa ), /* properties_required */ |
| 0, /* properties_provided */ |
| 0, /* properties_destroyed */ |
| 0, /* todo_flags_start */ |
| 0, /* todo_flags_finish */ |
| }; |
| |
| class pass_tail_calls : public gimple_opt_pass |
| { |
| public: |
| pass_tail_calls (gcc::context *ctxt) |
| : gimple_opt_pass (pass_data_tail_calls, ctxt) |
| {} |
| |
| /* opt_pass methods: */ |
| virtual bool gate (function *) { return gate_tail_calls (); } |
| virtual unsigned int execute (function *) { return execute_tail_calls (); } |
| |
| }; // class pass_tail_calls |
| |
| } // anon namespace |
| |
| gimple_opt_pass * |
| make_pass_tail_calls (gcc::context *ctxt) |
| { |
| return new pass_tail_calls (ctxt); |
| } |