gcc/tree-tailcall.c

   1 /* Tail call optimization on trees.
   2    Copyright (C) 2003-2013 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 3, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "tm.h"
  24 #include "tree.h"
  25 #include "tm_p.h"
  26 #include "basic-block.h"
  27 #include "function.h"
  28 #include "tree-ssa.h"
  29 #include "gimple-pretty-print.h"
  30 #include "except.h"
  31 #include "tree-pass.h"
  32 #include "flags.h"
  33 #include "langhooks.h"
  34 #include "dbgcnt.h"
  35 #include "target.h"
  36 #include "cfgloop.h"
  37 #include "common/common-target.h"
  38 #include "ipa-utils.h"
  39
  40 /* The file implements the tail recursion elimination.  It is also used to
  41    analyze the tail calls in general, passing the results to the rtl level
  42    where they are used for sibcall optimization.
  43
  44    In addition to the standard tail recursion elimination, we handle the most
  45    trivial cases of making the call tail recursive by creating accumulators.
  46    For example the following function
  47
  48    int sum (int n)
  49    {
  50      if (n > 0)
  51        return n + sum (n - 1);
  52      else
  53        return 0;
  54    }
  55
  56    is transformed into
  57
  58    int sum (int n)
  59    {
  60      int acc = 0;
  61
  62      while (n > 0)
  63        acc += n--;
  64
  65      return acc;
  66    }
  67
  68    To do this, we maintain two accumulators (a_acc and m_acc) that indicate
  69    when we reach the return x statement, we should return a_acc + x * m_acc
  70    instead.  They are initially initialized to 0 and 1, respectively,
  71    so the semantics of the function is obviously preserved.  If we are
  72    guaranteed that the value of the accumulator never change, we
  73    omit the accumulator.
  74
  75    There are three cases how the function may exit.  The first one is
  76    handled in adjust_return_value, the other two in adjust_accumulator_values
  77    (the second case is actually a special case of the third one and we
  78    present it separately just for clarity):
  79
  80    1) Just return x, where x is not in any of the remaining special shapes.
  81       We rewrite this to a gimple equivalent of return m_acc * x + a_acc.
  82
  83    2) return f (...), where f is the current function, is rewritten in a
  84       classical tail-recursion elimination way, into assignment of arguments
  85       and jump to the start of the function.  Values of the accumulators
  86       are unchanged.
  87
  88    3) return a + m * f(...), where a and m do not depend on call to f.
  89       To preserve the semantics described before we want this to be rewritten
  90       in such a way that we finally return
  91
  92       a_acc + (a + m * f(...)) * m_acc = (a_acc + a * m_acc) + (m * m_acc) * f(...).
  93
  94       I.e. we increase a_acc by a * m_acc, multiply m_acc by m and
  95       eliminate the tail call to f.  Special cases when the value is just
  96       added or just multiplied are obtained by setting a = 0 or m = 1.
  97
  98    TODO -- it is possible to do similar tricks for other operations.  */
  99
 100 /* A structure that describes the tailcall.  */
 101
 102 struct tailcall
 103 {
 104   /* The iterator pointing to the call statement.  */
 105   gimple_stmt_iterator call_gsi;
 106
 107   /* True if it is a call to the current function.  */
 108   bool tail_recursion;
 109
 110   /* The return value of the caller is mult * f + add, where f is the return
 111      value of the call.  */
 112   tree mult, add;
 113
 114   /* Next tailcall in the chain.  */
 115   struct tailcall *next;
 116 };
 117
 118 /* The variables holding the value of multiplicative and additive
 119    accumulator.  */
 120 static tree m_acc, a_acc;
 121
 122 static bool suitable_for_tail_opt_p (void);
 123 static bool optimize_tail_call (struct tailcall *, bool);
 124 static void eliminate_tail_call (struct tailcall *);
 125 static void find_tail_calls (basic_block, struct tailcall **);
 126
 127 /* Returns false when the function is not suitable for tail call optimization
 128    from some reason (e.g. if it takes variable number of arguments).  */
 129
 130 static bool
 131 suitable_for_tail_opt_p (void)
 132 {
 133   if (cfun->stdarg)
 134     return false;
 135
 136   return true;
 137 }
 138 /* Returns false when the function is not suitable for tail call optimization
 139    from some reason (e.g. if it takes variable number of arguments).
 140    This test must pass in addition to suitable_for_tail_opt_p in order to make
 141    tail call discovery happen.  */
 142
 143 static bool
 144 suitable_for_tail_call_opt_p (void)
 145 {
 146   tree param;
 147
 148   /* alloca (until we have stack slot life analysis) inhibits
 149      sibling call optimizations, but not tail recursion.  */
 150   if (cfun->calls_alloca)
 151     return false;
 152
 153   /* If we are using sjlj exceptions, we may need to add a call to
 154      _Unwind_SjLj_Unregister at exit of the function.  Which means
 155      that we cannot do any sibcall transformations.  */
 156   if (targetm_common.except_unwind_info (&global_options) == UI_SJLJ
 157       && current_function_has_exception_handlers ())
 158     return false;
 159
 160   /* Any function that calls setjmp might have longjmp called from
 161      any called function.  ??? We really should represent this
 162      properly in the CFG so that this needn't be special cased.  */
 163   if (cfun->calls_setjmp)
 164     return false;
 165
 166   /* ??? It is OK if the argument of a function is taken in some cases,
 167      but not in all cases.  See PR15387 and PR19616.  Revisit for 4.1.  */
 168   for (param = DECL_ARGUMENTS (current_function_decl);
 169        param;
 170        param = DECL_CHAIN (param))
 171     if (TREE_ADDRESSABLE (param))
 172       return false;
 173
 174   return true;
 175 }
 176
 177 /* Checks whether the expression EXPR in stmt AT is independent of the
 178    statement pointed to by GSI (in a sense that we already know EXPR's value
 179    at GSI).  We use the fact that we are only called from the chain of
 180    basic blocks that have only single successor.  Returns the expression
 181    containing the value of EXPR at GSI.  */
 182
 183 static tree
 184 independent_of_stmt_p (tree expr, gimple at, gimple_stmt_iterator gsi)
 185 {
 186   basic_block bb, call_bb, at_bb;
 187   edge e;
 188   edge_iterator ei;
 189
 190   if (is_gimple_min_invariant (expr))
 191     return expr;
 192
 193   if (TREE_CODE (expr) != SSA_NAME)
 194     return NULL_TREE;
 195
 196   /* Mark the blocks in the chain leading to the end.  */
 197   at_bb = gimple_bb (at);
 198   call_bb = gimple_bb (gsi_stmt (gsi));
 199   for (bb = call_bb; bb != at_bb; bb = single_succ (bb))
 200     bb->aux = &bb->aux;
 201   bb->aux = &bb->aux;
 202
 203   while (1)
 204     {
 205       at = SSA_NAME_DEF_STMT (expr);
 206       bb = gimple_bb (at);
 207
 208       /* The default definition or defined before the chain.  */
 209       if (!bb || !bb->aux)
 210         break;
 211
 212       if (bb == call_bb)
 213         {
 214           for (; !gsi_end_p (gsi); gsi_next (&gsi))
 215             if (gsi_stmt (gsi) == at)
 216               break;
 217
 218           if (!gsi_end_p (gsi))
 219             expr = NULL_TREE;
 220           break;
 221         }
 222
 223       if (gimple_code (at) != GIMPLE_PHI)
 224         {
 225           expr = NULL_TREE;
 226           break;
 227         }
 228
 229       FOR_EACH_EDGE (e, ei, bb->preds)
 230         if (e->src->aux)
 231           break;
 232       gcc_assert (e);
 233
 234       expr = PHI_ARG_DEF_FROM_EDGE (at, e);
 235       if (TREE_CODE (expr) != SSA_NAME)
 236         {
 237           /* The value is a constant.  */
 238           break;
 239         }
 240     }
 241
 242   /* Unmark the blocks.  */
 243   for (bb = call_bb; bb != at_bb; bb = single_succ (bb))
 244     bb->aux = NULL;
 245   bb->aux = NULL;
 246
 247   return expr;
 248 }
 249
 250 /* Simulates the effect of an assignment STMT on the return value of the tail
 251    recursive CALL passed in ASS_VAR.  M and A are the multiplicative and the
 252    additive factor for the real return value.  */
 253
 254 static bool
 255 process_assignment (gimple stmt, gimple_stmt_iterator call, tree *m,
 256                     tree *a, tree *ass_var)
 257 {
 258   tree op0, op1 = NULL_TREE, non_ass_var = NULL_TREE;
 259   tree dest = gimple_assign_lhs (stmt);
 260   enum tree_code code = gimple_assign_rhs_code (stmt);
 261   enum gimple_rhs_class rhs_class = get_gimple_rhs_class (code);
 262   tree src_var = gimple_assign_rhs1 (stmt);
 263
 264   /* See if this is a simple copy operation of an SSA name to the function
 265      result.  In that case we may have a simple tail call.  Ignore type
 266      conversions that can never produce extra code between the function
 267      call and the function return.  */
 268   if ((rhs_class == GIMPLE_SINGLE_RHS || gimple_assign_cast_p (stmt))
 269       && (TREE_CODE (src_var) == SSA_NAME))
 270     {
 271       /* Reject a tailcall if the type conversion might need
 272          additional code.  */
 273       if (gimple_assign_cast_p (stmt)
 274           && TYPE_MODE (TREE_TYPE (dest)) != TYPE_MODE (TREE_TYPE (src_var)))
 275         return false;
 276
 277       if (src_var != *ass_var)
 278         return false;
 279
 280       *ass_var = dest;
 281       return true;
 282     }
 283
 284   switch (rhs_class)
 285     {
 286     case GIMPLE_BINARY_RHS:
 287       op1 = gimple_assign_rhs2 (stmt);
 288
 289       /* Fall through.  */
 290
 291     case GIMPLE_UNARY_RHS:
 292       op0 = gimple_assign_rhs1 (stmt);
 293       break;
 294
 295     default:
 296       return false;
 297     }
 298
 299   /* Accumulator optimizations will reverse the order of operations.
 300      We can only do that for floating-point types if we're assuming
 301      that addition and multiplication are associative.  */
 302   if (!flag_associative_math)
 303     if (FLOAT_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl))))
 304       return false;
 305
 306   if (rhs_class == GIMPLE_UNARY_RHS)
 307     ;
 308   else if (op0 == *ass_var
 309            && (non_ass_var = independent_of_stmt_p (op1, stmt, call)))
 310     ;
 311   else if (op1 == *ass_var
 312            && (non_ass_var = independent_of_stmt_p (op0, stmt, call)))
 313     ;
 314   else
 315     return false;
 316
 317   switch (code)
 318     {
 319     case PLUS_EXPR:
 320       *a = non_ass_var;
 321       *ass_var = dest;
 322       return true;
 323
 324     case POINTER_PLUS_EXPR:
 325       if (op0 != *ass_var)
 326         return false;
 327       *a = non_ass_var;
 328       *ass_var = dest;
 329       return true;
 330
 331     case MULT_EXPR:
 332       *m = non_ass_var;
 333       *ass_var = dest;
 334       return true;
 335
 336     case NEGATE_EXPR:
 337       *m = build_minus_one_cst (TREE_TYPE (op0));
 338       *ass_var = dest;
 339       return true;
 340
 341     case MINUS_EXPR:
 342       if (*ass_var == op0)
 343         *a = fold_build1 (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var);
 344       else
 345         {
 346           *m = build_minus_one_cst (TREE_TYPE (non_ass_var));
 347           *a = fold_build1 (NEGATE_EXPR, TREE_TYPE (non_ass_var), non_ass_var);
 348         }
 349
 350       *ass_var = dest;
 351       return true;
 352
 353       /* TODO -- Handle POINTER_PLUS_EXPR.  */
 354
 355     default:
 356       return false;
 357     }
 358 }
 359
 360 /* Propagate VAR through phis on edge E.  */
 361
 362 static tree
 363 propagate_through_phis (tree var, edge e)
 364 {
 365   basic_block dest = e->dest;
 366   gimple_stmt_iterator gsi;
 367
 368   for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
 369     {
 370       gimple phi = gsi_stmt (gsi);
 371       if (PHI_ARG_DEF_FROM_EDGE (phi, e) == var)
 372         return PHI_RESULT (phi);
 373     }
 374   return var;
 375 }
 376
 377 /* Finds tailcalls falling into basic block BB. The list of found tailcalls is
 378    added to the start of RET.  */
 379
 380 static void
 381 find_tail_calls (basic_block bb, struct tailcall **ret)
 382 {
 383   tree ass_var = NULL_TREE, ret_var, func, param;
 384   gimple stmt, call = NULL;
 385   gimple_stmt_iterator gsi, agsi;
 386   bool tail_recursion;
 387   struct tailcall *nw;
 388   edge e;
 389   tree m, a;
 390   basic_block abb;
 391   size_t idx;
 392   tree var;
 393
 394   if (!single_succ_p (bb))
 395     return;
 396
 397   for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
 398     {
 399       stmt = gsi_stmt (gsi);
 400
 401       /* Ignore labels, returns, clobbers and debug stmts.  */
 402       if (gimple_code (stmt) == GIMPLE_LABEL
 403           || gimple_code (stmt) == GIMPLE_RETURN
 404           || gimple_clobber_p (stmt)
 405           || is_gimple_debug (stmt))
 406         continue;
 407
 408       /* Check for a call.  */
 409       if (is_gimple_call (stmt))
 410         {
 411           call = stmt;
 412           ass_var = gimple_call_lhs (stmt);
 413           break;
 414         }
 415
 416       /* If the statement references memory or volatile operands, fail.  */
 417       if (gimple_references_memory_p (stmt)
 418           || gimple_has_volatile_ops (stmt))
 419         return;
 420     }
 421
 422   if (gsi_end_p (gsi))
 423     {
 424       edge_iterator ei;
 425       /* Recurse to the predecessors.  */
 426       FOR_EACH_EDGE (e, ei, bb->preds)
 427         find_tail_calls (e->src, ret);
 428
 429       return;
 430     }
 431
 432   /* If the LHS of our call is not just a simple register, we can't
 433      transform this into a tail or sibling call.  This situation happens,
 434      in (e.g.) "*p = foo()" where foo returns a struct.  In this case
 435      we won't have a temporary here, but we need to carry out the side
 436      effect anyway, so tailcall is impossible.
 437
 438      ??? In some situations (when the struct is returned in memory via
 439      invisible argument) we could deal with this, e.g. by passing 'p'
 440      itself as that argument to foo, but it's too early to do this here,
 441      and expand_call() will not handle it anyway.  If it ever can, then
 442      we need to revisit this here, to allow that situation.  */
 443   if (ass_var && !is_gimple_reg (ass_var))
 444     return;
 445
 446   /* We found the call, check whether it is suitable.  */
 447   tail_recursion = false;
 448   func = gimple_call_fndecl (call);
 449   if (func && recursive_call_p (current_function_decl, func))
 450     {
 451       tree arg;
 452
 453       for (param = DECL_ARGUMENTS (func), idx = 0;
 454            param && idx < gimple_call_num_args (call);
 455            param = DECL_CHAIN (param), idx ++)
 456         {
 457           arg = gimple_call_arg (call, idx);
 458           if (param != arg)
 459             {
 460               /* Make sure there are no problems with copying.  The parameter
 461                  have a copyable type and the two arguments must have reasonably
 462                  equivalent types.  The latter requirement could be relaxed if
 463                  we emitted a suitable type conversion statement.  */
 464               if (!is_gimple_reg_type (TREE_TYPE (param))
 465                   || !useless_type_conversion_p (TREE_TYPE (param),
 466                                                  TREE_TYPE (arg)))
 467                 break;
 468
 469               /* The parameter should be a real operand, so that phi node
 470                  created for it at the start of the function has the meaning
 471                  of copying the value.  This test implies is_gimple_reg_type
 472                  from the previous condition, however this one could be
 473                  relaxed by being more careful with copying the new value
 474                  of the parameter (emitting appropriate GIMPLE_ASSIGN and
 475                  updating the virtual operands).  */
 476               if (!is_gimple_reg (param))
 477                 break;
 478             }
 479         }
 480       if (idx == gimple_call_num_args (call) && !param)
 481         tail_recursion = true;
 482     }
 483
 484   /* Make sure the tail invocation of this function does not refer
 485      to local variables.  */
 486   FOR_EACH_LOCAL_DECL (cfun, idx, var)
 487     {
 488       if (TREE_CODE (var) != PARM_DECL
 489           && auto_var_in_fn_p (var, cfun->decl)
 490           && (ref_maybe_used_by_stmt_p (call, var)
 491               || call_may_clobber_ref_p (call, var)))
 492         return;
 493     }
 494
 495   /* Now check the statements after the call.  None of them has virtual
 496      operands, so they may only depend on the call through its return
 497      value.  The return value should also be dependent on each of them,
 498      since we are running after dce.  */
 499   m = NULL_TREE;
 500   a = NULL_TREE;
 501
 502   abb = bb;
 503   agsi = gsi;
 504   while (1)
 505     {
 506       tree tmp_a = NULL_TREE;
 507       tree tmp_m = NULL_TREE;
 508       gsi_next (&agsi);
 509
 510       while (gsi_end_p (agsi))
 511         {
 512           ass_var = propagate_through_phis (ass_var, single_succ_edge (abb));
 513           abb = single_succ (abb);
 514           agsi = gsi_start_bb (abb);
 515         }
 516
 517       stmt = gsi_stmt (agsi);
 518
 519       if (gimple_code (stmt) == GIMPLE_LABEL)
 520         continue;
 521
 522       if (gimple_code (stmt) == GIMPLE_RETURN)
 523         break;
 524
 525       if (gimple_clobber_p (stmt))
 526         continue;
 527
 528       if (is_gimple_debug (stmt))
 529         continue;
 530
 531       if (gimple_code (stmt) != GIMPLE_ASSIGN)
 532         return;
 533
 534       /* This is a gimple assign. */
 535       if (! process_assignment (stmt, gsi, &tmp_m, &tmp_a, &ass_var))
 536         return;
 537
 538       if (tmp_a)
 539         {
 540           tree type = TREE_TYPE (tmp_a);
 541           if (a)
 542             a = fold_build2 (PLUS_EXPR, type, fold_convert (type, a), tmp_a);
 543           else
 544             a = tmp_a;
 545         }
 546       if (tmp_m)
 547         {
 548           tree type = TREE_TYPE (tmp_m);
 549           if (m)
 550             m = fold_build2 (MULT_EXPR, type, fold_convert (type, m), tmp_m);
 551           else
 552             m = tmp_m;
 553
 554           if (a)
 555             a = fold_build2 (MULT_EXPR, type, fold_convert (type, a), tmp_m);
 556         }
 557     }
 558
 559   /* See if this is a tail call we can handle.  */
 560   ret_var = gimple_return_retval (stmt);
 561
 562   /* We may proceed if there either is no return value, or the return value
 563      is identical to the call's return.  */
 564   if (ret_var
 565       && (ret_var != ass_var))
 566     return;
 567
 568   /* If this is not a tail recursive call, we cannot handle addends or
 569      multiplicands.  */
 570   if (!tail_recursion && (m || a))
 571     return;
 572
 573   /* For pointers only allow additions.  */
 574   if (m && POINTER_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl))))
 575     return;
 576
 577   nw = XNEW (struct tailcall);
 578
 579   nw->call_gsi = gsi;
 580
 581   nw->tail_recursion = tail_recursion;
 582
 583   nw->mult = m;
 584   nw->add = a;
 585
 586   nw->next = *ret;
 587   *ret = nw;
 588 }
 589
 590 /* Helper to insert PHI_ARGH to the phi of VAR in the destination of edge E.  */
 591
 592 static void
 593 add_successor_phi_arg (edge e, tree var, tree phi_arg)
 594 {
 595   gimple_stmt_iterator gsi;
 596
 597   for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
 598     if (PHI_RESULT (gsi_stmt (gsi)) == var)
 599       break;
 600
 601   gcc_assert (!gsi_end_p (gsi));
 602   add_phi_arg (gsi_stmt (gsi), phi_arg, e, UNKNOWN_LOCATION);
 603 }
 604
 605 /* Creates a GIMPLE statement which computes the operation specified by
 606    CODE, ACC and OP1 to a new variable with name LABEL and inserts the
 607    statement in the position specified by GSI.  Returns the
 608    tree node of the statement's result.  */
 609
 610 static tree
 611 adjust_return_value_with_ops (enum tree_code code, const char *label,
 612                               tree acc, tree op1, gimple_stmt_iterator gsi)
 613 {
 614
 615   tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
 616   tree result = make_temp_ssa_name (ret_type, NULL, label);
 617   gimple stmt;
 618
 619   if (POINTER_TYPE_P (ret_type))
 620     {
 621       gcc_assert (code == PLUS_EXPR && TREE_TYPE (acc) == sizetype);
 622       code = POINTER_PLUS_EXPR;
 623     }
 624   if (types_compatible_p (TREE_TYPE (acc), TREE_TYPE (op1))
 625       && code != POINTER_PLUS_EXPR)
 626     stmt = gimple_build_assign_with_ops (code, result, acc, op1);
 627   else
 628     {
 629       tree tem;
 630       if (code == POINTER_PLUS_EXPR)
 631         tem = fold_build2 (code, TREE_TYPE (op1), op1, acc);
 632       else
 633         tem = fold_build2 (code, TREE_TYPE (op1),
 634                            fold_convert (TREE_TYPE (op1), acc), op1);
 635       tree rhs = fold_convert (ret_type, tem);
 636       rhs = force_gimple_operand_gsi (&gsi, rhs,
 637                                       false, NULL, true, GSI_SAME_STMT);
 638       stmt = gimple_build_assign (result, rhs);
 639     }
 640
 641   gsi_insert_before (&gsi, stmt, GSI_NEW_STMT);
 642   return result;
 643 }
 644
 645 /* Creates a new GIMPLE statement that adjusts the value of accumulator ACC by
 646    the computation specified by CODE and OP1 and insert the statement
 647    at the position specified by GSI as a new statement.  Returns new SSA name
 648    of updated accumulator.  */
 649
 650 static tree
 651 update_accumulator_with_ops (enum tree_code code, tree acc, tree op1,
 652                              gimple_stmt_iterator gsi)
 653 {
 654   gimple stmt;
 655   tree var = copy_ssa_name (acc, NULL);
 656   if (types_compatible_p (TREE_TYPE (acc), TREE_TYPE (op1)))
 657     stmt = gimple_build_assign_with_ops (code, var, acc, op1);
 658   else
 659     {
 660       tree rhs = fold_convert (TREE_TYPE (acc),
 661                                fold_build2 (code,
 662                                             TREE_TYPE (op1),
 663                                             fold_convert (TREE_TYPE (op1), acc),
 664                                             op1));
 665       rhs = force_gimple_operand_gsi (&gsi, rhs,
 666                                       false, NULL, false, GSI_CONTINUE_LINKING);
 667       stmt = gimple_build_assign (var, rhs);
 668     }
 669   gsi_insert_after (&gsi, stmt, GSI_NEW_STMT);
 670   return var;
 671 }
 672
 673 /* Adjust the accumulator values according to A and M after GSI, and update
 674    the phi nodes on edge BACK.  */
 675
 676 static void
 677 adjust_accumulator_values (gimple_stmt_iterator gsi, tree m, tree a, edge back)
 678 {
 679   tree var, a_acc_arg, m_acc_arg;
 680
 681   if (m)
 682     m = force_gimple_operand_gsi (&gsi, m, true, NULL, true, GSI_SAME_STMT);
 683   if (a)
 684     a = force_gimple_operand_gsi (&gsi, a, true, NULL, true, GSI_SAME_STMT);
 685
 686   a_acc_arg = a_acc;
 687   m_acc_arg = m_acc;
 688   if (a)
 689     {
 690       if (m_acc)
 691         {
 692           if (integer_onep (a))
 693             var = m_acc;
 694           else
 695             var = adjust_return_value_with_ops (MULT_EXPR, "acc_tmp", m_acc,
 696                                                 a, gsi);
 697         }
 698       else
 699         var = a;
 700
 701       a_acc_arg = update_accumulator_with_ops (PLUS_EXPR, a_acc, var, gsi);
 702     }
 703
 704   if (m)
 705     m_acc_arg = update_accumulator_with_ops (MULT_EXPR, m_acc, m, gsi);
 706
 707   if (a_acc)
 708     add_successor_phi_arg (back, a_acc, a_acc_arg);
 709
 710   if (m_acc)
 711     add_successor_phi_arg (back, m_acc, m_acc_arg);
 712 }
 713
 714 /* Adjust value of the return at the end of BB according to M and A
 715    accumulators.  */
 716
 717 static void
 718 adjust_return_value (basic_block bb, tree m, tree a)
 719 {
 720   tree retval;
 721   gimple ret_stmt = gimple_seq_last_stmt (bb_seq (bb));
 722   gimple_stmt_iterator gsi = gsi_last_bb (bb);
 723
 724   gcc_assert (gimple_code (ret_stmt) == GIMPLE_RETURN);
 725
 726   retval = gimple_return_retval (ret_stmt);
 727   if (!retval || retval == error_mark_node)
 728     return;
 729
 730   if (m)
 731     retval = adjust_return_value_with_ops (MULT_EXPR, "mul_tmp", m_acc, retval,
 732                                            gsi);
 733   if (a)
 734     retval = adjust_return_value_with_ops (PLUS_EXPR, "acc_tmp", a_acc, retval,
 735                                            gsi);
 736   gimple_return_set_retval (ret_stmt, retval);
 737   update_stmt (ret_stmt);
 738 }
 739
 740 /* Subtract COUNT and FREQUENCY from the basic block and it's
 741    outgoing edge.  */
 742 static void
 743 decrease_profile (basic_block bb, gcov_type count, int frequency)
 744 {
 745   edge e;
 746   bb->count -= count;
 747   if (bb->count < 0)
 748     bb->count = 0;
 749   bb->frequency -= frequency;
 750   if (bb->frequency < 0)
 751     bb->frequency = 0;
 752   if (!single_succ_p (bb))
 753     {
 754       gcc_assert (!EDGE_COUNT (bb->succs));
 755       return;
 756     }
 757   e = single_succ_edge (bb);
 758   e->count -= count;
 759   if (e->count < 0)
 760     e->count = 0;
 761 }
 762
 763 /* Returns true if argument PARAM of the tail recursive call needs to be copied
 764    when the call is eliminated.  */
 765
 766 static bool
 767 arg_needs_copy_p (tree param)
 768 {
 769   tree def;
 770
 771   if (!is_gimple_reg (param))
 772     return false;
 773
 774   /* Parameters that are only defined but never used need not be copied.  */
 775   def = ssa_default_def (cfun, param);
 776   if (!def)
 777     return false;
 778
 779   return true;
 780 }
 781
 782 /* Eliminates tail call described by T.  TMP_VARS is a list of
 783    temporary variables used to copy the function arguments.  */
 784
 785 static void
 786 eliminate_tail_call (struct tailcall *t)
 787 {
 788   tree param, rslt;
 789   gimple stmt, call;
 790   tree arg;
 791   size_t idx;
 792   basic_block bb, first;
 793   edge e;
 794   gimple phi;
 795   gimple_stmt_iterator gsi;
 796   gimple orig_stmt;
 797
 798   stmt = orig_stmt = gsi_stmt (t->call_gsi);
 799   bb = gsi_bb (t->call_gsi);
 800
 801   if (dump_file && (dump_flags & TDF_DETAILS))
 802     {
 803       fprintf (dump_file, "Eliminated tail recursion in bb %d : ",
 804                bb->index);
 805       print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
 806       fprintf (dump_file, "\n");
 807     }
 808
 809   gcc_assert (is_gimple_call (stmt));
 810
 811   first = single_succ (ENTRY_BLOCK_PTR);
 812
 813   /* Remove the code after call_gsi that will become unreachable.  The
 814      possibly unreachable code in other blocks is removed later in
 815      cfg cleanup.  */
 816   gsi = t->call_gsi;
 817   gsi_next (&gsi);
 818   while (!gsi_end_p (gsi))
 819     {
 820       gimple t = gsi_stmt (gsi);
 821       /* Do not remove the return statement, so that redirect_edge_and_branch
 822          sees how the block ends.  */
 823       if (gimple_code (t) == GIMPLE_RETURN)
 824         break;
 825
 826       gsi_remove (&gsi, true);
 827       release_defs (t);
 828     }
 829
 830   /* Number of executions of function has reduced by the tailcall.  */
 831   e = single_succ_edge (gsi_bb (t->call_gsi));
 832   decrease_profile (EXIT_BLOCK_PTR, e->count, EDGE_FREQUENCY (e));
 833   decrease_profile (ENTRY_BLOCK_PTR, e->count, EDGE_FREQUENCY (e));
 834   if (e->dest != EXIT_BLOCK_PTR)
 835     decrease_profile (e->dest, e->count, EDGE_FREQUENCY (e));
 836
 837   /* Replace the call by a jump to the start of function.  */
 838   e = redirect_edge_and_branch (single_succ_edge (gsi_bb (t->call_gsi)),
 839                                 first);
 840   gcc_assert (e);
 841   PENDING_STMT (e) = NULL;
 842
 843   /* Add phi node entries for arguments.  The ordering of the phi nodes should
 844      be the same as the ordering of the arguments.  */
 845   for (param = DECL_ARGUMENTS (current_function_decl),
 846          idx = 0, gsi = gsi_start_phis (first);
 847        param;
 848        param = DECL_CHAIN (param), idx++)
 849     {
 850       if (!arg_needs_copy_p (param))
 851         continue;
 852
 853       arg = gimple_call_arg (stmt, idx);
 854       phi = gsi_stmt (gsi);
 855       gcc_assert (param == SSA_NAME_VAR (PHI_RESULT (phi)));
 856
 857       add_phi_arg (phi, arg, e, gimple_location (stmt));
 858       gsi_next (&gsi);
 859     }
 860
 861   /* Update the values of accumulators.  */
 862   adjust_accumulator_values (t->call_gsi, t->mult, t->add, e);
 863
 864   call = gsi_stmt (t->call_gsi);
 865   rslt = gimple_call_lhs (call);
 866   if (rslt != NULL_TREE)
 867     {
 868       /* Result of the call will no longer be defined.  So adjust the
 869          SSA_NAME_DEF_STMT accordingly.  */
 870       SSA_NAME_DEF_STMT (rslt) = gimple_build_nop ();
 871     }
 872
 873   gsi_remove (&t->call_gsi, true);
 874   release_defs (call);
 875 }
 876
 877 /* Optimizes the tailcall described by T.  If OPT_TAILCALLS is true, also
 878    mark the tailcalls for the sibcall optimization.  */
 879
 880 static bool
 881 optimize_tail_call (struct tailcall *t, bool opt_tailcalls)
 882 {
 883   if (t->tail_recursion)
 884     {
 885       eliminate_tail_call (t);
 886       return true;
 887     }
 888
 889   if (opt_tailcalls)
 890     {
 891       gimple stmt = gsi_stmt (t->call_gsi);
 892
 893       gimple_call_set_tail (stmt, true);
 894       if (dump_file && (dump_flags & TDF_DETAILS))
 895         {
 896           fprintf (dump_file, "Found tail call ");
 897           print_gimple_stmt (dump_file, stmt, 0, dump_flags);
 898           fprintf (dump_file, " in bb %i\n", (gsi_bb (t->call_gsi))->index);
 899         }
 900     }
 901
 902   return false;
 903 }
 904
 905 /* Creates a tail-call accumulator of the same type as the return type of the
 906    current function.  LABEL is the name used to creating the temporary
 907    variable for the accumulator.  The accumulator will be inserted in the
 908    phis of a basic block BB with single predecessor with an initial value
 909    INIT converted to the current function return type.  */
 910
 911 static tree
 912 create_tailcall_accumulator (const char *label, basic_block bb, tree init)
 913 {
 914   tree ret_type = TREE_TYPE (DECL_RESULT (current_function_decl));
 915   if (POINTER_TYPE_P (ret_type))
 916     ret_type = sizetype;
 917
 918   tree tmp = make_temp_ssa_name (ret_type, NULL, label);
 919   gimple phi;
 920
 921   phi = create_phi_node (tmp, bb);
 922   /* RET_TYPE can be a float when -ffast-maths is enabled.  */
 923   add_phi_arg (phi, fold_convert (ret_type, init), single_pred_edge (bb),
 924                UNKNOWN_LOCATION);
 925   return PHI_RESULT (phi);
 926 }
 927
 928 /* Optimizes tail calls in the function, turning the tail recursion
 929    into iteration.  */
 930
 931 static unsigned int
 932 tree_optimize_tail_calls_1 (bool opt_tailcalls)
 933 {
 934   edge e;
 935   bool phis_constructed = false;
 936   struct tailcall *tailcalls = NULL, *act, *next;
 937   bool changed = false;
 938   basic_block first = single_succ (ENTRY_BLOCK_PTR);
 939   tree param;
 940   gimple stmt;
 941   edge_iterator ei;
 942
 943   if (!suitable_for_tail_opt_p ())
 944     return 0;
 945   if (opt_tailcalls)
 946     opt_tailcalls = suitable_for_tail_call_opt_p ();
 947
 948   FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
 949     {
 950       /* Only traverse the normal exits, i.e. those that end with return
 951          statement.  */
 952       stmt = last_stmt (e->src);
 953
 954       if (stmt
 955           && gimple_code (stmt) == GIMPLE_RETURN)
 956         find_tail_calls (e->src, &tailcalls);
 957     }
 958
 959   /* Construct the phi nodes and accumulators if necessary.  */
 960   a_acc = m_acc = NULL_TREE;
 961   for (act = tailcalls; act; act = act->next)
 962     {
 963       if (!act->tail_recursion)
 964         continue;
 965
 966       if (!phis_constructed)
 967         {
 968           /* Ensure that there is only one predecessor of the block
 969              or if there are existing degenerate PHI nodes.  */
 970           if (!single_pred_p (first)
 971               || !gimple_seq_empty_p (phi_nodes (first)))
 972             first = split_edge (single_succ_edge (ENTRY_BLOCK_PTR));
 973
 974           /* Copy the args if needed.  */
 975           for (param = DECL_ARGUMENTS (current_function_decl);
 976                param;
 977                param = DECL_CHAIN (param))
 978             if (arg_needs_copy_p (param))
 979               {
 980                 tree name = ssa_default_def (cfun, param);
 981                 tree new_name = make_ssa_name (param, SSA_NAME_DEF_STMT (name));
 982                 gimple phi;
 983
 984                 set_ssa_default_def (cfun, param, new_name);
 985                 phi = create_phi_node (name, first);
 986                 add_phi_arg (phi, new_name, single_pred_edge (first),
 987                              EXPR_LOCATION (param));
 988               }
 989           phis_constructed = true;
 990         }
 991
 992       if (act->add && !a_acc)
 993         a_acc = create_tailcall_accumulator ("add_acc", first,
 994                                              integer_zero_node);
 995
 996       if (act->mult && !m_acc)
 997         m_acc = create_tailcall_accumulator ("mult_acc", first,
 998                                              integer_one_node);
 999     }
1000
1001   if (a_acc || m_acc)
1002     {
1003       /* When the tail call elimination using accumulators is performed,
1004          statements adding the accumulated value are inserted at all exits.
1005          This turns all other tail calls to non-tail ones.  */
1006       opt_tailcalls = false;
1007     }
1008
1009   for (; tailcalls; tailcalls = next)
1010     {
1011       next = tailcalls->next;
1012       changed |= optimize_tail_call (tailcalls, opt_tailcalls);
1013       free (tailcalls);
1014     }
1015
1016   if (a_acc || m_acc)
1017     {
1018       /* Modify the remaining return statements.  */
1019       FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
1020         {
1021           stmt = last_stmt (e->src);
1022
1023           if (stmt
1024               && gimple_code (stmt) == GIMPLE_RETURN)
1025             adjust_return_value (e->src, m_acc, a_acc);
1026         }
1027     }
1028
1029   if (changed)
1030     {
1031       /* We may have created new loops.  Make them magically appear.  */
1032       if (current_loops)
1033         loops_state_set (LOOPS_NEED_FIXUP);
1034       free_dominance_info (CDI_DOMINATORS);
1035     }
1036
1037   /* Add phi nodes for the virtual operands defined in the function to the
1038      header of the loop created by tail recursion elimination.  Do so
1039      by triggering the SSA renamer.  */
1040   if (phis_constructed)
1041     mark_virtual_operands_for_renaming (cfun);
1042
1043   if (changed)
1044     return TODO_cleanup_cfg | TODO_update_ssa_only_virtuals;
1045   return 0;
1046 }
1047
1048 static unsigned int
1049 execute_tail_recursion (void)
1050 {
1051   return tree_optimize_tail_calls_1 (false);
1052 }
1053
1054 static bool
1055 gate_tail_calls (void)
1056 {
1057   return flag_optimize_sibling_calls != 0 && dbg_cnt (tail_call);
1058 }
1059
1060 static unsigned int
1061 execute_tail_calls (void)
1062 {
1063   return tree_optimize_tail_calls_1 (true);
1064 }
1065
1066 namespace {
1067
1068 const pass_data pass_data_tail_recursion =
1069 {
1070   GIMPLE_PASS, /* type */
1071   "tailr", /* name */
1072   OPTGROUP_NONE, /* optinfo_flags */
1073   true, /* has_gate */
1074   true, /* has_execute */
1075   TV_NONE, /* tv_id */
1076   ( PROP_cfg | PROP_ssa ), /* properties_required */
1077   0, /* properties_provided */
1078   0, /* properties_destroyed */
1079   0, /* todo_flags_start */
1080   TODO_verify_ssa, /* todo_flags_finish */
1081 };
1082
1083 class pass_tail_recursion : public gimple_opt_pass
1084 {
1085 public:
1086   pass_tail_recursion(gcc::context *ctxt)
1087     : gimple_opt_pass(pass_data_tail_recursion, ctxt)
1088   {}
1089
1090   /* opt_pass methods: */
1091   opt_pass * clone () { return new pass_tail_recursion (ctxt_); }
1092   bool gate () { return gate_tail_calls (); }
1093   unsigned int execute () { return execute_tail_recursion (); }
1094
1095 }; // class pass_tail_recursion
1096
1097 } // anon namespace
1098
1099 gimple_opt_pass *
1100 make_pass_tail_recursion (gcc::context *ctxt)
1101 {
1102   return new pass_tail_recursion (ctxt);
1103 }
1104
1105 namespace {
1106
1107 const pass_data pass_data_tail_calls =
1108 {
1109   GIMPLE_PASS, /* type */
1110   "tailc", /* name */
1111   OPTGROUP_NONE, /* optinfo_flags */
1112   true, /* has_gate */
1113   true, /* has_execute */
1114   TV_NONE, /* tv_id */
1115   ( PROP_cfg | PROP_ssa ), /* properties_required */
1116   0, /* properties_provided */
1117   0, /* properties_destroyed */
1118   0, /* todo_flags_start */
1119   TODO_verify_ssa, /* todo_flags_finish */
1120 };
1121
1122 class pass_tail_calls : public gimple_opt_pass
1123 {
1124 public:
1125   pass_tail_calls(gcc::context *ctxt)
1126     : gimple_opt_pass(pass_data_tail_calls, ctxt)
1127   {}
1128
1129   /* opt_pass methods: */
1130   bool gate () { return gate_tail_calls (); }
1131   unsigned int execute () { return execute_tail_calls (); }
1132
1133 }; // class pass_tail_calls
1134
1135 } // anon namespace
1136
1137 gimple_opt_pass *
1138 make_pass_tail_calls (gcc::context *ctxt)
1139 {
1140   return new pass_tail_calls (ctxt);
1141 }