gcc/c/c-fold.c

   1 /* Support for fully folding sub-trees of an expression for C compiler.
   2    Copyright (C) 1992-2017 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 it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 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 "target.h"
  24 #include "function.h"
  25 #include "bitmap.h"
  26 #include "c-tree.h"
  27 #include "intl.h"
  28 #include "gimplify.h"
  29
  30 static tree c_fully_fold_internal (tree expr, bool, bool *, bool *, bool);
  31
  32 /* If DISABLE is true, stop issuing warnings.  This is used when
  33    parsing code that we know will not be executed.  This function may
  34    be called multiple times, and works as a stack.  */
  35
  36 static void
  37 c_disable_warnings (bool disable)
  38 {
  39   if (disable)
  40     {
  41       ++c_inhibit_evaluation_warnings;
  42       fold_defer_overflow_warnings ();
  43     }
  44 }
  45
  46 /* If ENABLE is true, reenable issuing warnings.  */
  47
  48 static void
  49 c_enable_warnings (bool enable)
  50 {
  51   if (enable)
  52     {
  53       --c_inhibit_evaluation_warnings;
  54       fold_undefer_and_ignore_overflow_warnings ();
  55     }
  56 }
  57
  58 /* Fully fold EXPR, an expression that was not folded (beyond integer
  59    constant expressions and null pointer constants) when being built
  60    up.  If IN_INIT, this is in a static initializer and certain
  61    changes are made to the folding done.  Clear *MAYBE_CONST if
  62    MAYBE_CONST is not NULL and EXPR is definitely not a constant
  63    expression because it contains an evaluated operator (in C99) or an
  64    operator outside of sizeof returning an integer constant (in C90)
  65    not permitted in constant expressions, or because it contains an
  66    evaluated arithmetic overflow.  (*MAYBE_CONST should typically be
  67    set to true by callers before calling this function.)  Return the
  68    folded expression.  Function arguments have already been folded
  69    before calling this function, as have the contents of SAVE_EXPR,
  70    TARGET_EXPR, BIND_EXPR, VA_ARG_EXPR, OBJ_TYPE_REF and
  71    C_MAYBE_CONST_EXPR.  */
  72
  73 tree
  74 c_fully_fold (tree expr, bool in_init, bool *maybe_const)
  75 {
  76   tree ret;
  77   tree eptype = NULL_TREE;
  78   bool dummy = true;
  79   bool maybe_const_itself = true;
  80   location_t loc = EXPR_LOCATION (expr);
  81
  82   if (!maybe_const)
  83     maybe_const = &dummy;
  84   if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
  85     {
  86       eptype = TREE_TYPE (expr);
  87       expr = TREE_OPERAND (expr, 0);
  88     }
  89   ret = c_fully_fold_internal (expr, in_init, maybe_const,
  90                                &maybe_const_itself, false);
  91   if (eptype)
  92     ret = fold_convert_loc (loc, eptype, ret);
  93   *maybe_const &= maybe_const_itself;
  94   return ret;
  95 }
  96
  97 /* Internal helper for c_fully_fold.  EXPR and IN_INIT are as for
  98    c_fully_fold.  *MAYBE_CONST_OPERANDS is cleared because of operands
  99    not permitted, while *MAYBE_CONST_ITSELF is cleared because of
 100    arithmetic overflow (for C90, *MAYBE_CONST_OPERANDS is carried from
 101    both evaluated and unevaluated subexpressions while
 102    *MAYBE_CONST_ITSELF is carried from only evaluated
 103    subexpressions).  FOR_INT_CONST indicates if EXPR is an expression
 104    with integer constant operands, and if any of the operands doesn't
 105    get folded to an integer constant, don't fold the expression itself.  */
 106
 107 static tree
 108 c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
 109                        bool *maybe_const_itself, bool for_int_const)
 110 {
 111   tree ret = expr;
 112   enum tree_code code = TREE_CODE (expr);
 113   enum tree_code_class kind = TREE_CODE_CLASS (code);
 114   location_t loc = EXPR_LOCATION (expr);
 115   tree op0, op1, op2, op3;
 116   tree orig_op0, orig_op1, orig_op2;
 117   bool op0_const = true, op1_const = true, op2_const = true;
 118   bool op0_const_self = true, op1_const_self = true, op2_const_self = true;
 119   bool nowarning = TREE_NO_WARNING (expr);
 120   bool unused_p;
 121   source_range old_range;
 122
 123   /* Constants, declarations, statements, errors, SAVE_EXPRs and
 124      anything else not counted as an expression cannot usefully be
 125      folded further at this point.  */
 126   if (!IS_EXPR_CODE_CLASS (kind)
 127       || kind == tcc_statement
 128       || code == SAVE_EXPR)
 129     return expr;
 130
 131   if (IS_EXPR_CODE_CLASS (kind))
 132     old_range = EXPR_LOCATION_RANGE (expr);
 133
 134   /* Operands of variable-length expressions (function calls) have
 135      already been folded, as have __builtin_* function calls, and such
 136      expressions cannot occur in constant expressions.  */
 137   if (kind == tcc_vl_exp)
 138     {
 139       *maybe_const_operands = false;
 140       ret = fold (expr);
 141       goto out;
 142     }
 143
 144   if (code == C_MAYBE_CONST_EXPR)
 145     {
 146       tree pre = C_MAYBE_CONST_EXPR_PRE (expr);
 147       tree inner = C_MAYBE_CONST_EXPR_EXPR (expr);
 148       if (C_MAYBE_CONST_EXPR_NON_CONST (expr))
 149         *maybe_const_operands = false;
 150       if (C_MAYBE_CONST_EXPR_INT_OPERANDS (expr))
 151         {
 152           *maybe_const_itself = false;
 153           inner = c_fully_fold_internal (inner, in_init, maybe_const_operands,
 154                                          maybe_const_itself, true);
 155         }
 156       if (pre && !in_init)
 157         ret = build2 (COMPOUND_EXPR, TREE_TYPE (expr), pre, inner);
 158       else
 159         ret = inner;
 160       goto out;
 161     }
 162
 163   /* Assignment, increment, decrement, function call and comma
 164      operators, and statement expressions, cannot occur in constant
 165      expressions if evaluated / outside of sizeof.  (Function calls
 166      were handled above, though VA_ARG_EXPR is treated like a function
 167      call here, and statement expressions are handled through
 168      C_MAYBE_CONST_EXPR to avoid folding inside them.)  */
 169   switch (code)
 170     {
 171     case MODIFY_EXPR:
 172     case PREDECREMENT_EXPR:
 173     case PREINCREMENT_EXPR:
 174     case POSTDECREMENT_EXPR:
 175     case POSTINCREMENT_EXPR:
 176     case COMPOUND_EXPR:
 177       *maybe_const_operands = false;
 178       break;
 179
 180     case VA_ARG_EXPR:
 181     case TARGET_EXPR:
 182     case BIND_EXPR:
 183     case OBJ_TYPE_REF:
 184       *maybe_const_operands = false;
 185       ret = fold (expr);
 186       goto out;
 187
 188     default:
 189       break;
 190     }
 191
 192   /* Fold individual tree codes as appropriate.  */
 193   switch (code)
 194     {
 195     case COMPOUND_LITERAL_EXPR:
 196       /* Any non-constancy will have been marked in a containing
 197          C_MAYBE_CONST_EXPR; there is no more folding to do here.  */
 198       goto out;
 199
 200     case COMPONENT_REF:
 201       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 202       op1 = TREE_OPERAND (expr, 1);
 203       op2 = TREE_OPERAND (expr, 2);
 204       op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
 205                                    maybe_const_itself, for_int_const);
 206       STRIP_TYPE_NOPS (op0);
 207       if (op0 != orig_op0)
 208         ret = build3 (COMPONENT_REF, TREE_TYPE (expr), op0, op1, op2);
 209       if (ret != expr)
 210         {
 211           TREE_READONLY (ret) = TREE_READONLY (expr);
 212           TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
 213         }
 214       goto out;
 215
 216     case ARRAY_REF:
 217       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 218       orig_op1 = op1 = TREE_OPERAND (expr, 1);
 219       op2 = TREE_OPERAND (expr, 2);
 220       op3 = TREE_OPERAND (expr, 3);
 221       op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
 222                                    maybe_const_itself, for_int_const);
 223       STRIP_TYPE_NOPS (op0);
 224       op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
 225                                    maybe_const_itself, for_int_const);
 226       STRIP_TYPE_NOPS (op1);
 227       op1 = decl_constant_value_for_optimization (op1);
 228       if (op0 != orig_op0 || op1 != orig_op1)
 229         ret = build4 (ARRAY_REF, TREE_TYPE (expr), op0, op1, op2, op3);
 230       if (ret != expr)
 231         {
 232           TREE_READONLY (ret) = TREE_READONLY (expr);
 233           TREE_SIDE_EFFECTS (ret) = TREE_SIDE_EFFECTS (expr);
 234           TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
 235         }
 236       ret = fold (ret);
 237       goto out;
 238
 239     case COMPOUND_EXPR:
 240     case MODIFY_EXPR:
 241     case PREDECREMENT_EXPR:
 242     case PREINCREMENT_EXPR:
 243     case POSTDECREMENT_EXPR:
 244     case POSTINCREMENT_EXPR:
 245     case PLUS_EXPR:
 246     case MINUS_EXPR:
 247     case MULT_EXPR:
 248     case POINTER_PLUS_EXPR:
 249     case TRUNC_DIV_EXPR:
 250     case CEIL_DIV_EXPR:
 251     case FLOOR_DIV_EXPR:
 252     case TRUNC_MOD_EXPR:
 253     case RDIV_EXPR:
 254     case EXACT_DIV_EXPR:
 255     case LSHIFT_EXPR:
 256     case RSHIFT_EXPR:
 257     case BIT_IOR_EXPR:
 258     case BIT_XOR_EXPR:
 259     case BIT_AND_EXPR:
 260     case LT_EXPR:
 261     case LE_EXPR:
 262     case GT_EXPR:
 263     case GE_EXPR:
 264     case EQ_EXPR:
 265     case NE_EXPR:
 266     case COMPLEX_EXPR:
 267     case TRUTH_AND_EXPR:
 268     case TRUTH_OR_EXPR:
 269     case TRUTH_XOR_EXPR:
 270     case UNORDERED_EXPR:
 271     case ORDERED_EXPR:
 272     case UNLT_EXPR:
 273     case UNLE_EXPR:
 274     case UNGT_EXPR:
 275     case UNGE_EXPR:
 276     case UNEQ_EXPR:
 277       /* Binary operations evaluating both arguments (increment and
 278          decrement are binary internally in GCC).  */
 279       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 280       orig_op1 = op1 = TREE_OPERAND (expr, 1);
 281       op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
 282                                    maybe_const_itself, for_int_const);
 283       STRIP_TYPE_NOPS (op0);
 284       if (code != MODIFY_EXPR
 285           && code != PREDECREMENT_EXPR
 286           && code != PREINCREMENT_EXPR
 287           && code != POSTDECREMENT_EXPR
 288           && code != POSTINCREMENT_EXPR)
 289         op0 = decl_constant_value_for_optimization (op0);
 290       /* The RHS of a MODIFY_EXPR was fully folded when building that
 291          expression for the sake of conversion warnings.  */
 292       if (code != MODIFY_EXPR)
 293         op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
 294                                      maybe_const_itself, for_int_const);
 295       STRIP_TYPE_NOPS (op1);
 296       op1 = decl_constant_value_for_optimization (op1);
 297
 298       if (for_int_const && (TREE_CODE (op0) != INTEGER_CST
 299                             || TREE_CODE (op1) != INTEGER_CST))
 300         goto out;
 301
 302       if (op0 != orig_op0 || op1 != orig_op1 || in_init)
 303         ret = in_init
 304           ? fold_build2_initializer_loc (loc, code, TREE_TYPE (expr), op0, op1)
 305           : fold_build2_loc (loc, code, TREE_TYPE (expr), op0, op1);
 306       else
 307         ret = fold (expr);
 308       if (TREE_OVERFLOW_P (ret)
 309           && !TREE_OVERFLOW_P (op0)
 310           && !TREE_OVERFLOW_P (op1))
 311         overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), ret);
 312       if (code == LSHIFT_EXPR
 313           && TREE_CODE (orig_op0) != INTEGER_CST
 314           && TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
 315           && TREE_CODE (op0) == INTEGER_CST
 316           && c_inhibit_evaluation_warnings == 0
 317           && tree_int_cst_sgn (op0) < 0)
 318         warning_at (loc, OPT_Wshift_negative_value,
 319                     "left shift of negative value");
 320       if ((code == LSHIFT_EXPR || code == RSHIFT_EXPR)
 321           && TREE_CODE (orig_op1) != INTEGER_CST
 322           && TREE_CODE (op1) == INTEGER_CST
 323           && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE
 324           && c_inhibit_evaluation_warnings == 0)
 325         {
 326           if (tree_int_cst_sgn (op1) < 0)
 327             warning_at (loc, OPT_Wshift_count_negative,
 328                         (code == LSHIFT_EXPR
 329                          ? G_("left shift count is negative")
 330                          : G_("right shift count is negative")));
 331           else if ((TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
 332                     || TREE_CODE (TREE_TYPE (orig_op0)) == FIXED_POINT_TYPE)
 333                    && compare_tree_int (op1,
 334                                         TYPE_PRECISION (TREE_TYPE (orig_op0)))
 335                       >= 0)
 336             warning_at (loc, OPT_Wshift_count_overflow,
 337                         (code == LSHIFT_EXPR
 338                          ? G_("left shift count >= width of type")
 339                          : G_("right shift count >= width of type")));
 340           else if (TREE_CODE (TREE_TYPE (orig_op0)) == VECTOR_TYPE
 341                    && compare_tree_int (op1,
 342                                         TYPE_PRECISION (TREE_TYPE (TREE_TYPE (orig_op0))))
 343                       >= 0)
 344             warning_at (loc, OPT_Wshift_count_overflow,
 345                         code == LSHIFT_EXPR
 346                         ? G_("left shift count >= width of vector element")
 347                         : G_("right shift count >= width of vector element"));
 348         }
 349       if (code == LSHIFT_EXPR
 350           /* If either OP0 has been folded to INTEGER_CST...  */
 351           && ((TREE_CODE (orig_op0) != INTEGER_CST
 352                && TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
 353                && TREE_CODE (op0) == INTEGER_CST)
 354               /* ...or if OP1 has been folded to INTEGER_CST...  */
 355               || (TREE_CODE (orig_op1) != INTEGER_CST
 356                   && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE
 357                   && TREE_CODE (op1) == INTEGER_CST))
 358           && c_inhibit_evaluation_warnings == 0)
 359         /* ...then maybe we can detect an overflow.  */
 360         maybe_warn_shift_overflow (loc, op0, op1);
 361       if ((code == TRUNC_DIV_EXPR
 362            || code == CEIL_DIV_EXPR
 363            || code == FLOOR_DIV_EXPR
 364            || code == EXACT_DIV_EXPR
 365            || code == TRUNC_MOD_EXPR)
 366           && TREE_CODE (orig_op1) != INTEGER_CST
 367           && TREE_CODE (op1) == INTEGER_CST
 368           && (TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
 369               || TREE_CODE (TREE_TYPE (orig_op0)) == FIXED_POINT_TYPE)
 370           && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE)
 371         warn_for_div_by_zero (loc, op1);
 372       goto out;
 373
 374     case INDIRECT_REF:
 375     case FIX_TRUNC_EXPR:
 376     case FLOAT_EXPR:
 377     CASE_CONVERT:
 378     case ADDR_SPACE_CONVERT_EXPR:
 379     case VIEW_CONVERT_EXPR:
 380     case NON_LVALUE_EXPR:
 381     case NEGATE_EXPR:
 382     case BIT_NOT_EXPR:
 383     case TRUTH_NOT_EXPR:
 384     case ADDR_EXPR:
 385     case CONJ_EXPR:
 386     case REALPART_EXPR:
 387     case IMAGPART_EXPR:
 388       /* Unary operations.  */
 389       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 390       op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
 391                                    maybe_const_itself, for_int_const);
 392       STRIP_TYPE_NOPS (op0);
 393       if (code != ADDR_EXPR && code != REALPART_EXPR && code != IMAGPART_EXPR)
 394         op0 = decl_constant_value_for_optimization (op0);
 395
 396       if (for_int_const && TREE_CODE (op0) != INTEGER_CST)
 397         goto out;
 398
 399       /* ??? Cope with user tricks that amount to offsetof.  The middle-end is
 400          not prepared to deal with them if they occur in initializers.  */
 401       if (op0 != orig_op0
 402           && code == ADDR_EXPR
 403           && (op1 = get_base_address (op0)) != NULL_TREE
 404           && INDIRECT_REF_P (op1)
 405           && TREE_CONSTANT (TREE_OPERAND (op1, 0)))
 406         ret = fold_convert_loc (loc, TREE_TYPE (expr), fold_offsetof_1 (op0));
 407       else if (op0 != orig_op0 || in_init)
 408         ret = in_init
 409           ? fold_build1_initializer_loc (loc, code, TREE_TYPE (expr), op0)
 410           : fold_build1_loc (loc, code, TREE_TYPE (expr), op0);
 411       else
 412         ret = fold (expr);
 413       if (code == INDIRECT_REF
 414           && ret != expr
 415           && INDIRECT_REF_P (ret))
 416         {
 417           TREE_READONLY (ret) = TREE_READONLY (expr);
 418           TREE_SIDE_EFFECTS (ret) = TREE_SIDE_EFFECTS (expr);
 419           TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
 420         }
 421       switch (code)
 422         {
 423         case FIX_TRUNC_EXPR:
 424         case FLOAT_EXPR:
 425         CASE_CONVERT:
 426           /* Don't warn about explicit conversions.  We will already
 427              have warned about suspect implicit conversions.  */
 428           break;
 429
 430         default:
 431           if (TREE_OVERFLOW_P (ret) && !TREE_OVERFLOW_P (op0))
 432             overflow_warning (EXPR_LOCATION (expr), ret);
 433           break;
 434         }
 435       goto out;
 436
 437     case TRUTH_ANDIF_EXPR:
 438     case TRUTH_ORIF_EXPR:
 439       /* Binary operations not necessarily evaluating both
 440          arguments.  */
 441       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 442       orig_op1 = op1 = TREE_OPERAND (expr, 1);
 443       op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self,
 444                                    for_int_const);
 445       STRIP_TYPE_NOPS (op0);
 446
 447       unused_p = (op0 == (code == TRUTH_ANDIF_EXPR
 448                           ? truthvalue_false_node
 449                           : truthvalue_true_node));
 450       c_disable_warnings (unused_p);
 451       op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self,
 452                                    for_int_const);
 453       STRIP_TYPE_NOPS (op1);
 454       c_enable_warnings (unused_p);
 455
 456       if (for_int_const
 457           && (TREE_CODE (op0) != INTEGER_CST
 458               /* Require OP1 be an INTEGER_CST only if it's evaluated.  */
 459               || (!unused_p && TREE_CODE (op1) != INTEGER_CST)))
 460         goto out;
 461
 462       if (op0 != orig_op0 || op1 != orig_op1 || in_init)
 463         ret = in_init
 464           ? fold_build2_initializer_loc (loc, code, TREE_TYPE (expr), op0, op1)
 465           : fold_build2_loc (loc, code, TREE_TYPE (expr), op0, op1);
 466       else
 467         ret = fold (expr);
 468       *maybe_const_operands &= op0_const;
 469       *maybe_const_itself &= op0_const_self;
 470       if (!(flag_isoc99
 471             && op0_const
 472             && op0_const_self
 473             && (code == TRUTH_ANDIF_EXPR
 474                 ? op0 == truthvalue_false_node
 475                 : op0 == truthvalue_true_node)))
 476         *maybe_const_operands &= op1_const;
 477       if (!(op0_const
 478             && op0_const_self
 479             && (code == TRUTH_ANDIF_EXPR
 480                 ? op0 == truthvalue_false_node
 481                 : op0 == truthvalue_true_node)))
 482         *maybe_const_itself &= op1_const_self;
 483       goto out;
 484
 485     case COND_EXPR:
 486       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 487       orig_op1 = op1 = TREE_OPERAND (expr, 1);
 488       orig_op2 = op2 = TREE_OPERAND (expr, 2);
 489       op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self,
 490                                    for_int_const);
 491
 492       STRIP_TYPE_NOPS (op0);
 493       c_disable_warnings (op0 == truthvalue_false_node);
 494       op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self,
 495                                    for_int_const);
 496       STRIP_TYPE_NOPS (op1);
 497       c_enable_warnings (op0 == truthvalue_false_node);
 498
 499       c_disable_warnings (op0 == truthvalue_true_node);
 500       op2 = c_fully_fold_internal (op2, in_init, &op2_const, &op2_const_self,
 501                                    for_int_const);
 502       STRIP_TYPE_NOPS (op2);
 503       c_enable_warnings (op0 == truthvalue_true_node);
 504
 505       if (for_int_const
 506           && (TREE_CODE (op0) != INTEGER_CST
 507               /* Only the evaluated operand must be an INTEGER_CST.  */
 508               || (op0 == truthvalue_true_node
 509                   ? TREE_CODE (op1) != INTEGER_CST
 510                   : TREE_CODE (op2) != INTEGER_CST)))
 511         goto out;
 512
 513       if (op0 != orig_op0 || op1 != orig_op1 || op2 != orig_op2)
 514         ret = fold_build3_loc (loc, code, TREE_TYPE (expr), op0, op1, op2);
 515       else
 516         ret = fold (expr);
 517       *maybe_const_operands &= op0_const;
 518       *maybe_const_itself &= op0_const_self;
 519       if (!(flag_isoc99
 520             && op0_const
 521             && op0_const_self
 522             && op0 == truthvalue_false_node))
 523         *maybe_const_operands &= op1_const;
 524       if (!(op0_const
 525             && op0_const_self
 526             && op0 == truthvalue_false_node))
 527         *maybe_const_itself &= op1_const_self;
 528       if (!(flag_isoc99
 529             && op0_const
 530             && op0_const_self
 531             && op0 == truthvalue_true_node))
 532         *maybe_const_operands &= op2_const;
 533       if (!(op0_const
 534             && op0_const_self
 535             && op0 == truthvalue_true_node))
 536         *maybe_const_itself &= op2_const_self;
 537       goto out;
 538
 539     case VEC_COND_EXPR:
 540       orig_op0 = op0 = TREE_OPERAND (expr, 0);
 541       orig_op1 = op1 = TREE_OPERAND (expr, 1);
 542       orig_op2 = op2 = TREE_OPERAND (expr, 2);
 543       op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
 544                                    maybe_const_itself, for_int_const);
 545       STRIP_TYPE_NOPS (op0);
 546       op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
 547                                    maybe_const_itself, for_int_const);
 548       STRIP_TYPE_NOPS (op1);
 549       op2 = c_fully_fold_internal (op2, in_init, maybe_const_operands,
 550                                    maybe_const_itself, for_int_const);
 551       STRIP_TYPE_NOPS (op2);
 552
 553       if (op0 != orig_op0 || op1 != orig_op1 || op2 != orig_op2)
 554         ret = fold_build3_loc (loc, code, TREE_TYPE (expr), op0, op1, op2);
 555       else
 556         ret = fold (expr);
 557       goto out;
 558
 559     case EXCESS_PRECISION_EXPR:
 560       /* Each case where an operand with excess precision may be
 561          encountered must remove the EXCESS_PRECISION_EXPR around
 562          inner operands and possibly put one around the whole
 563          expression or possibly convert to the semantic type (which
 564          c_fully_fold does); we cannot tell at this stage which is
 565          appropriate in any particular case.  */
 566       gcc_unreachable ();
 567
 568     default:
 569       /* Various codes may appear through folding built-in functions
 570          and their arguments.  */
 571       goto out;
 572     }
 573
 574  out:
 575   /* Some folding may introduce NON_LVALUE_EXPRs; all lvalue checks
 576      have been done by this point, so remove them again.  */
 577   nowarning |= TREE_NO_WARNING (ret);
 578   STRIP_TYPE_NOPS (ret);
 579   if (nowarning && !TREE_NO_WARNING (ret))
 580     {
 581       if (!CAN_HAVE_LOCATION_P (ret))
 582         ret = build1 (NOP_EXPR, TREE_TYPE (ret), ret);
 583       TREE_NO_WARNING (ret) = 1;
 584     }
 585   if (ret != expr)
 586     {
 587       protected_set_expr_location (ret, loc);
 588       if (IS_EXPR_CODE_CLASS (kind))
 589         set_source_range (ret, old_range.m_start, old_range.m_finish);
 590     }
 591   return ret;
 592 }
 593
 594 /* If not optimizing, EXP is not a VAR_DECL, or EXP has array type,
 595    return EXP.  Otherwise, return either EXP or its known constant
 596    value (if it has one), but return EXP if EXP has mode BLKmode.  ???
 597    Is the BLKmode test appropriate?  */
 598
 599 tree
 600 decl_constant_value_for_optimization (tree exp)
 601 {
 602   tree ret;
 603
 604   if (!optimize
 605       || !VAR_P (exp)
 606       || TREE_CODE (TREE_TYPE (exp)) == ARRAY_TYPE
 607       || DECL_MODE (exp) == BLKmode)
 608     return exp;
 609
 610   ret = decl_constant_value (exp);
 611   /* Avoid unwanted tree sharing between the initializer and current
 612      function's body where the tree can be modified e.g. by the
 613      gimplifier.  */
 614   if (ret != exp && TREE_STATIC (exp))
 615     ret = unshare_expr (ret);
 616   return ret;
 617 }