gcc/cp/expr.c

   1 /* Convert language-specific tree expression to rtl instructions,
   2    for GNU compiler.
   3    Copyright (C) 1988-2020 Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 3, or (at your option)
  10 any later version.
  11
  12 GCC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "cp-tree.h"
  26
  27 /* Expand C++-specific constants.  Currently, this means PTRMEM_CST.  */
  28
  29 tree
  30 cplus_expand_constant (tree cst)
  31 {
  32   switch (TREE_CODE (cst))
  33     {
  34     case PTRMEM_CST:
  35       {
  36         tree type = TREE_TYPE (cst);
  37         tree member;
  38
  39         /* Find the member.  */
  40         member = PTRMEM_CST_MEMBER (cst);
  41
  42         /* We can't lower this until the class is complete.  */
  43         if (!COMPLETE_TYPE_P (DECL_CONTEXT (member)))
  44           return cst;
  45
  46         if (TREE_CODE (member) == FIELD_DECL)
  47           {
  48             /* Find the offset for the field.  */
  49             cst = byte_position (member);
  50             while (!same_type_p (DECL_CONTEXT (member),
  51                                  TYPE_PTRMEM_CLASS_TYPE (type)))
  52               {
  53                 /* The MEMBER must have been nestled within an
  54                    anonymous aggregate contained in TYPE.  Find the
  55                    anonymous aggregate.  */
  56                 member = lookup_anon_field (TYPE_PTRMEM_CLASS_TYPE (type),
  57                                             DECL_CONTEXT (member));
  58                 cst = size_binop (PLUS_EXPR, cst, byte_position (member));
  59               }
  60             cst = fold (build_nop (type, cst));
  61           }
  62         else
  63           {
  64             tree delta;
  65             tree pfn;
  66
  67             expand_ptrmemfunc_cst (cst, &delta, &pfn);
  68             cst = build_ptrmemfunc1 (type, delta, pfn);
  69           }
  70       }
  71       break;
  72
  73     case CONSTRUCTOR:
  74       {
  75         constructor_elt *elt;
  76         unsigned HOST_WIDE_INT idx;
  77         FOR_EACH_VEC_SAFE_ELT (CONSTRUCTOR_ELTS (cst), idx, elt)
  78           elt->value = cplus_expand_constant (elt->value);
  79       }
  80
  81     default:
  82       /* There's nothing to do.  */
  83       break;
  84     }
  85
  86   return cst;
  87 }
  88
  89 /* We've seen an actual use of EXPR.  Possibly replace an outer variable
  90    reference inside with its constant value or a lambda capture.  */
  91
  92 tree
  93 mark_use (tree expr, bool rvalue_p, bool read_p,
  94           location_t loc /* = UNKNOWN_LOCATION */,
  95           bool reject_builtin /* = true */)
  96 {
  97 #define RECUR(t) mark_use ((t), rvalue_p, read_p, loc, reject_builtin)
  98
  99   if (expr == NULL_TREE || error_operand_p (expr))
 100     return expr;
 101
 102   if (reject_builtin && reject_gcc_builtin (expr, loc))
 103     return error_mark_node;
 104
 105   if (read_p)
 106     mark_exp_read (expr);
 107
 108   tree oexpr = expr;
 109   bool recurse_op[3] = { false, false, false };
 110   switch (TREE_CODE (expr))
 111     {
 112     case VAR_DECL:
 113     case PARM_DECL:
 114       if (rvalue_p && is_normal_capture_proxy (expr))
 115         {
 116           /* Look through capture by copy.  */
 117           tree cap = DECL_CAPTURED_VARIABLE (expr);
 118           if (TREE_CODE (TREE_TYPE (cap)) == TREE_CODE (TREE_TYPE (expr))
 119               && decl_constant_var_p (cap))
 120             {
 121               tree val = RECUR (cap);
 122               if (!is_capture_proxy (val))
 123                 {
 124                   tree l = current_lambda_expr ();
 125                   LAMBDA_EXPR_CAPTURE_OPTIMIZED (l) = true;
 126                 }
 127               return val;
 128             }
 129         }
 130       if (outer_automatic_var_p (expr)
 131           && decl_constant_var_p (expr))
 132         {
 133           if (rvalue_p)
 134             {
 135               tree t = maybe_constant_value (expr);
 136               if (TREE_CONSTANT (t))
 137                 {
 138                   expr = t;
 139                   break;
 140                 }
 141             }
 142           temp_override<location_t> l (input_location);
 143           if (loc != UNKNOWN_LOCATION)
 144             input_location = loc;
 145           expr = process_outer_var_ref (expr, tf_warning_or_error, true);
 146           if (!(TREE_TYPE (oexpr)
 147                 && TYPE_REF_P (TREE_TYPE (oexpr))))
 148             expr = convert_from_reference (expr);
 149         }
 150       break;
 151     case COMPONENT_REF:
 152     case NON_DEPENDENT_EXPR:
 153       recurse_op[0] = true;
 154       break;
 155     case COMPOUND_EXPR:
 156       recurse_op[1] = true;
 157       break;
 158     case COND_EXPR:
 159       recurse_op[2] = true;
 160       if (TREE_OPERAND (expr, 1))
 161         recurse_op[1] = true;
 162       break;
 163     case INDIRECT_REF:
 164       if (REFERENCE_REF_P (expr))
 165         {
 166           /* Try to look through the reference.  */
 167           tree ref = TREE_OPERAND (expr, 0);
 168           if (rvalue_p && is_normal_capture_proxy (ref))
 169             {
 170               /* Look through capture by reference.  */
 171               tree cap = DECL_CAPTURED_VARIABLE (ref);
 172               if (!TYPE_REF_P (TREE_TYPE (cap))
 173                   && decl_constant_var_p (cap))
 174                 {
 175                   tree val = RECUR (cap);
 176                   if (!is_capture_proxy (val))
 177                     {
 178                       tree l = current_lambda_expr ();
 179                       LAMBDA_EXPR_CAPTURE_OPTIMIZED (l) = true;
 180                     }
 181                   return val;
 182                 }
 183             }
 184           tree r = mark_rvalue_use (ref, loc, reject_builtin);
 185           if (r != ref)
 186             expr = convert_from_reference (r);
 187         }
 188       break;
 189
 190     case VIEW_CONVERT_EXPR:
 191       if (location_wrapper_p (expr))
 192         {
 193           loc = EXPR_LOCATION (expr);
 194           tree op = TREE_OPERAND (expr, 0);
 195           tree nop = RECUR (op);
 196           if (nop == error_mark_node)
 197             return error_mark_node;
 198           else if (op == nop)
 199             /* No change.  */;
 200           else if (DECL_P (nop) || CONSTANT_CLASS_P (nop))
 201             {
 202               /* Reuse the location wrapper.  */
 203               TREE_OPERAND (expr, 0) = nop;
 204               /* If we're replacing a DECL with a constant, we also need to
 205                  change the TREE_CODE of the location wrapper.  */
 206               if (rvalue_p)
 207                 TREE_SET_CODE (expr, NON_LVALUE_EXPR);
 208             }
 209           else
 210             {
 211               /* Drop the location wrapper.  */
 212               expr = nop;
 213               protected_set_expr_location (expr, loc);
 214             }
 215           return expr;
 216         }
 217       gcc_fallthrough();
 218     CASE_CONVERT:
 219       recurse_op[0] = true;
 220       break;
 221
 222     case MODIFY_EXPR:
 223         {
 224           tree lhs = TREE_OPERAND (expr, 0);
 225           /* [expr.ass] "A simple assignment whose left operand is of
 226              a volatile-qualified type is deprecated unless the assignment
 227              is either a discarded-value expression or appears in an
 228              unevaluated context."  */
 229           if (read_p
 230               && !cp_unevaluated_operand
 231               && (TREE_THIS_VOLATILE (lhs)
 232                   || CP_TYPE_VOLATILE_P (TREE_TYPE (lhs)))
 233               && !TREE_THIS_VOLATILE (expr))
 234             {
 235               warning_at (location_of (expr), OPT_Wvolatile,
 236                           "using value of simple assignment with %<volatile%>-"
 237                           "qualified left operand is deprecated");
 238               /* Make sure not to warn about this assignment again.  */
 239               TREE_THIS_VOLATILE (expr) = true;
 240             }
 241           break;
 242         }
 243
 244     default:
 245       break;
 246     }
 247
 248   for (int i = 0; i < 3; ++i)
 249     if (recurse_op[i])
 250       {
 251         tree op = TREE_OPERAND (expr, i);
 252         op = RECUR (op);
 253         if (op == error_mark_node)
 254           return error_mark_node;
 255         TREE_OPERAND (expr, i) = op;
 256       }
 257
 258   return expr;
 259 #undef RECUR
 260 }
 261
 262 /* Called whenever the expression EXPR is used in an rvalue context.
 263    When REJECT_BUILTIN is true the expression is checked to make sure
 264    it doesn't make it possible to obtain the address of a GCC built-in
 265    function with no library fallback (or any of its bits, such as in
 266    a conversion to bool).  */
 267
 268 tree
 269 mark_rvalue_use (tree e,
 270                  location_t loc /* = UNKNOWN_LOCATION */,
 271                  bool reject_builtin /* = true */)
 272 {
 273   return mark_use (e, true, true, loc, reject_builtin);
 274 }
 275
 276 /* Called whenever an expression is used in an lvalue context.  */
 277
 278 tree
 279 mark_lvalue_use (tree expr)
 280 {
 281   return mark_use (expr, false, true, input_location, false);
 282 }
 283
 284 /* As above, but don't consider this use a read.  */
 285
 286 tree
 287 mark_lvalue_use_nonread (tree expr)
 288 {
 289   return mark_use (expr, false, false, input_location, false);
 290 }
 291
 292 /* Called when expr appears as a discarded-value expression.  */
 293
 294 tree
 295 mark_discarded_use (tree expr)
 296 {
 297   /* The lvalue-to-rvalue conversion (7.1) is applied if and only if the
 298      expression is a glvalue of volatile-qualified type and it is one of the
 299      following:
 300      * ( expression ), where expression is one of these expressions,
 301      * id-expression (8.1.4),
 302      * subscripting (8.2.1),
 303      * class member access (8.2.5),
 304      * indirection (8.3.1),
 305      * pointer-to-member operation (8.5),
 306      * conditional expression (8.16) where both the second and the third
 307        operands are one of these expressions, or
 308      * comma expression (8.19) where the right operand is one of these
 309        expressions.  */
 310   if (expr == NULL_TREE)
 311     return expr;
 312
 313   STRIP_ANY_LOCATION_WRAPPER (expr);
 314
 315   switch (TREE_CODE (expr))
 316     {
 317     case COND_EXPR:
 318       TREE_OPERAND (expr, 2) = mark_discarded_use (TREE_OPERAND (expr, 2));
 319       gcc_fallthrough ();
 320     case COMPOUND_EXPR:
 321       TREE_OPERAND (expr, 1) = mark_discarded_use (TREE_OPERAND (expr, 1));
 322       return expr;
 323
 324     case COMPONENT_REF:
 325     case ARRAY_REF:
 326     case INDIRECT_REF:
 327     case MEMBER_REF:
 328       break;
 329     default:
 330       if (DECL_P (expr))
 331         break;
 332       else
 333         return expr;
 334     }
 335
 336   /* Like mark_rvalue_use, but don't reject built-ins.  */
 337   return mark_use (expr, true, true, input_location, false);
 338 }
 339
 340 /* Called whenever an expression is used in a type use context.  */
 341
 342 tree
 343 mark_type_use (tree expr)
 344 {
 345   mark_exp_read (expr);
 346   return expr;
 347 }
 348
 349 /* Mark EXP as read, not just set, for set but not used -Wunused
 350    warning purposes.  */
 351
 352 void
 353 mark_exp_read (tree exp)
 354 {
 355   if (exp == NULL)
 356     return;
 357
 358   switch (TREE_CODE (exp))
 359     {
 360     case VAR_DECL:
 361       if (DECL_DECOMPOSITION_P (exp))
 362         mark_exp_read (DECL_DECOMP_BASE (exp));
 363       gcc_fallthrough ();
 364     case PARM_DECL:
 365       DECL_READ_P (exp) = 1;
 366       break;
 367     case ARRAY_REF:
 368     case COMPONENT_REF:
 369     case MODIFY_EXPR:
 370     case REALPART_EXPR:
 371     case IMAGPART_EXPR:
 372     CASE_CONVERT:
 373     CASE_ADDR_EXPR:
 374     case INDIRECT_REF:
 375     case FLOAT_EXPR:
 376     case NON_DEPENDENT_EXPR:
 377     case VIEW_CONVERT_EXPR:
 378       mark_exp_read (TREE_OPERAND (exp, 0));
 379       break;
 380     case COMPOUND_EXPR:
 381       mark_exp_read (TREE_OPERAND (exp, 1));
 382       break;
 383     case COND_EXPR:
 384       if (TREE_OPERAND (exp, 1))
 385         mark_exp_read (TREE_OPERAND (exp, 1));
 386       if (TREE_OPERAND (exp, 2))
 387         mark_exp_read (TREE_OPERAND (exp, 2));
 388       break;
 389     default:
 390       break;
 391     }
 392 }
 393
 394 /* Fold X for consideration by one of the warning functions when checking
 395    whether an expression has a constant value.  */
 396
 397 tree
 398 fold_for_warn (tree x)
 399 {
 400   /* C++ implementation.  */
 401
 402   /* Prevent warning-dependent constexpr evaluation from changing
 403      DECL_UID (which breaks -fcompare-debug) and from instantiating
 404      templates.  */
 405   uid_sensitive_constexpr_evaluation_sentinel s;
 406
 407   /* It's not generally safe to fully fold inside of a template, so
 408      call fold_non_dependent_expr instead.  */
 409   if (processing_template_decl)
 410     {
 411       tree f = fold_non_dependent_expr (x, tf_none);
 412       if (f == error_mark_node)
 413         return x;
 414       else
 415         return f;
 416     }
 417   else if (cxx_dialect >= cxx11)
 418     x = maybe_constant_value (x);
 419
 420   return c_fully_fold (x, /*for_init*/false, /*maybe_constp*/NULL);
 421 }