gcc/cp/expr.cc

   1 /* Convert language-specific tree expression to rtl instructions,
   2    for GNU compiler.
   3    Copyright (C) 1988-2023 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           iloc_sentinel l (loc);
 143           expr = process_outer_var_ref (expr, tf_warning_or_error, true);
 144           if (!(TREE_TYPE (oexpr)
 145                 && TYPE_REF_P (TREE_TYPE (oexpr))))
 146             expr = convert_from_reference (expr);
 147         }
 148       break;
 149     case COMPONENT_REF:
 150       recurse_op[0] = true;
 151       break;
 152     case COMPOUND_EXPR:
 153       recurse_op[1] = true;
 154       break;
 155     case COND_EXPR:
 156       recurse_op[2] = true;
 157       if (TREE_OPERAND (expr, 1))
 158         recurse_op[1] = true;
 159       break;
 160     case INDIRECT_REF:
 161       if (REFERENCE_REF_P (expr))
 162         {
 163           /* Try to look through the reference.  */
 164           tree ref = TREE_OPERAND (expr, 0);
 165           if (rvalue_p && is_normal_capture_proxy (ref))
 166             {
 167               /* Look through capture by reference.  */
 168               tree cap = DECL_CAPTURED_VARIABLE (ref);
 169               if (!TYPE_REF_P (TREE_TYPE (cap))
 170                   && decl_constant_var_p (cap))
 171                 {
 172                   tree val = RECUR (cap);
 173                   if (!is_capture_proxy (val))
 174                     {
 175                       tree l = current_lambda_expr ();
 176                       LAMBDA_EXPR_CAPTURE_OPTIMIZED (l) = true;
 177                     }
 178                   return val;
 179                 }
 180             }
 181           tree r = mark_rvalue_use (ref, loc, reject_builtin);
 182           if (r != ref)
 183             expr = convert_from_reference (r);
 184         }
 185       break;
 186
 187     case VIEW_CONVERT_EXPR:
 188       if (location_wrapper_p (expr))
 189         {
 190           loc = EXPR_LOCATION (expr);
 191           tree op = TREE_OPERAND (expr, 0);
 192           tree nop = RECUR (op);
 193           if (nop == error_mark_node)
 194             return error_mark_node;
 195           else if (op == nop)
 196             /* No change.  */;
 197           else if (DECL_P (nop) || CONSTANT_CLASS_P (nop))
 198             {
 199               /* Reuse the location wrapper.  */
 200               TREE_OPERAND (expr, 0) = nop;
 201               /* If we're replacing a DECL with a constant, we also need to
 202                  change the TREE_CODE of the location wrapper.  */
 203               if (rvalue_p)
 204                 TREE_SET_CODE (expr, NON_LVALUE_EXPR);
 205             }
 206           else
 207             {
 208               /* Drop the location wrapper.  */
 209               expr = nop;
 210               protected_set_expr_location (expr, loc);
 211             }
 212           return expr;
 213         }
 214       gcc_fallthrough();
 215     CASE_CONVERT:
 216       recurse_op[0] = true;
 217       break;
 218
 219     case MODIFY_EXPR:
 220         {
 221           tree lhs = TREE_OPERAND (expr, 0);
 222           /* [expr.ass] "An assignment whose left operand is of
 223              a volatile-qualified type is deprecated unless the assignment
 224              is either a discarded-value expression or appears in an
 225              unevaluated context."  */
 226           if (!cp_unevaluated_operand
 227               && (TREE_THIS_VOLATILE (lhs)
 228                   || CP_TYPE_VOLATILE_P (TREE_TYPE (lhs)))
 229               && !TREE_THIS_VOLATILE (expr))
 230             {
 231               if (warning_at (location_of (expr), OPT_Wvolatile,
 232                               "using value of assignment with "
 233                               "%<volatile%>-qualified left operand is "
 234                               "deprecated"))
 235                 /* Make sure not to warn about this assignment again.  */
 236                 TREE_THIS_VOLATILE (expr) = true;
 237             }
 238           break;
 239         }
 240
 241     default:
 242       break;
 243     }
 244
 245   for (int i = 0; i < 3; ++i)
 246     if (recurse_op[i])
 247       {
 248         tree op = TREE_OPERAND (expr, i);
 249         op = RECUR (op);
 250         if (op == error_mark_node)
 251           return error_mark_node;
 252         TREE_OPERAND (expr, i) = op;
 253       }
 254
 255   return expr;
 256 #undef RECUR
 257 }
 258
 259 /* Called whenever the expression EXPR is used in an rvalue context.
 260    When REJECT_BUILTIN is true the expression is checked to make sure
 261    it doesn't make it possible to obtain the address of a GCC built-in
 262    function with no library fallback (or any of its bits, such as in
 263    a conversion to bool).  */
 264
 265 tree
 266 mark_rvalue_use (tree e,
 267                  location_t loc /* = UNKNOWN_LOCATION */,
 268                  bool reject_builtin /* = true */)
 269 {
 270   return mark_use (e, true, true, loc, reject_builtin);
 271 }
 272
 273 /* Called whenever an expression is used in an lvalue context.  */
 274
 275 tree
 276 mark_lvalue_use (tree expr)
 277 {
 278   return mark_use (expr, false, true, input_location, false);
 279 }
 280
 281 /* As above, but don't consider this use a read.  */
 282
 283 tree
 284 mark_lvalue_use_nonread (tree expr)
 285 {
 286   return mark_use (expr, false, false, input_location, false);
 287 }
 288
 289 /* Called when expr appears as a discarded-value expression.  */
 290
 291 tree
 292 mark_discarded_use (tree expr)
 293 {
 294   /* The lvalue-to-rvalue conversion (7.1) is applied if and only if the
 295      expression is a glvalue of volatile-qualified type and it is one of the
 296      following:
 297      * ( expression ), where expression is one of these expressions,
 298      * id-expression (8.1.4),
 299      * subscripting (8.2.1),
 300      * class member access (8.2.5),
 301      * indirection (8.3.1),
 302      * pointer-to-member operation (8.5),
 303      * conditional expression (8.16) where both the second and the third
 304        operands are one of these expressions, or
 305      * comma expression (8.19) where the right operand is one of these
 306        expressions.  */
 307   if (expr == NULL_TREE)
 308     return expr;
 309
 310   STRIP_ANY_LOCATION_WRAPPER (expr);
 311
 312   switch (TREE_CODE (expr))
 313     {
 314     case COND_EXPR:
 315       TREE_OPERAND (expr, 2) = mark_discarded_use (TREE_OPERAND (expr, 2));
 316       gcc_fallthrough ();
 317     case COMPOUND_EXPR:
 318       TREE_OPERAND (expr, 1) = mark_discarded_use (TREE_OPERAND (expr, 1));
 319       return expr;
 320
 321     case COMPONENT_REF:
 322     case ARRAY_REF:
 323     case INDIRECT_REF:
 324     case MEMBER_REF:
 325       break;
 326     default:
 327       if (DECL_P (expr))
 328         break;
 329       else
 330         return expr;
 331     }
 332
 333   /* Like mark_rvalue_use, but don't reject built-ins.  */
 334   return mark_use (expr, true, true, input_location, false);
 335 }
 336
 337 /* Called whenever an expression is used in a type use context.  */
 338
 339 tree
 340 mark_type_use (tree expr)
 341 {
 342   mark_exp_read (expr);
 343   return expr;
 344 }
 345
 346 /* Mark EXP as read, not just set, for set but not used -Wunused
 347    warning purposes.  */
 348
 349 void
 350 mark_exp_read (tree exp)
 351 {
 352   if (exp == NULL)
 353     return;
 354
 355   switch (TREE_CODE (exp))
 356     {
 357     case VAR_DECL:
 358       if (DECL_DECOMPOSITION_P (exp))
 359         mark_exp_read (DECL_DECOMP_BASE (exp));
 360       gcc_fallthrough ();
 361     case PARM_DECL:
 362       DECL_READ_P (exp) = 1;
 363       break;
 364     case ARRAY_REF:
 365     case COMPONENT_REF:
 366     case MODIFY_EXPR:
 367     case REALPART_EXPR:
 368     case IMAGPART_EXPR:
 369     CASE_CONVERT:
 370     case ADDR_EXPR:
 371     case INDIRECT_REF:
 372     case FLOAT_EXPR:
 373     case VIEW_CONVERT_EXPR:
 374       mark_exp_read (TREE_OPERAND (exp, 0));
 375       break;
 376     case COMPOUND_EXPR:
 377       mark_exp_read (TREE_OPERAND (exp, 1));
 378       break;
 379     case COND_EXPR:
 380       if (TREE_OPERAND (exp, 1))
 381         mark_exp_read (TREE_OPERAND (exp, 1));
 382       if (TREE_OPERAND (exp, 2))
 383         mark_exp_read (TREE_OPERAND (exp, 2));
 384       break;
 385     default:
 386       break;
 387     }
 388 }
 389
 390 /* Fold X for consideration by one of the warning functions when checking
 391    whether an expression has a constant value.  */
 392
 393 tree
 394 fold_for_warn (tree x)
 395 {
 396   /* C++ implementation.  */
 397
 398   if (cp_unevaluated_operand)
 399     /* In an unevaluated context we don't care about the reduced value
 400        of an expression, so neither should any warnings.  */
 401     return x;
 402
 403   /* Prevent warning-dependent constexpr evaluation from changing
 404      DECL_UID (which breaks -fcompare-debug) and from instantiating
 405      templates.  */
 406   uid_sensitive_constexpr_evaluation_sentinel s;
 407
 408   /* It's not generally safe to fully fold inside of a template, so
 409      call fold_non_dependent_expr instead.  */
 410   if (processing_template_decl)
 411     {
 412       tree f = fold_non_dependent_expr (x, tf_none);
 413       if (f == error_mark_node)
 414         return x;
 415       else
 416         return f;
 417     }
 418   else if (cxx_dialect >= cxx11)
 419     x = maybe_constant_value (x);
 420
 421   return c_fully_fold (x, /*for_init*/false, /*maybe_constp*/NULL);
 422 }