1 /* Support for fully folding sub-trees of an expression for C compiler.
2 Copyright (C) 1992-2017 Free Software Foundation, Inc.
4 This file is part of GCC.
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
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
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/>. */
22 #include "coretypes.h"
30 static tree c_fully_fold_internal (tree expr, bool, bool *, bool *, bool,
33 /* If DISABLE is true, stop issuing warnings. This is used when
34 parsing code that we know will not be executed. This function may
35 be called multiple times, and works as a stack. */
38 c_disable_warnings (bool disable)
42 ++c_inhibit_evaluation_warnings;
43 fold_defer_overflow_warnings ();
47 /* If ENABLE is true, reenable issuing warnings. */
50 c_enable_warnings (bool enable)
54 --c_inhibit_evaluation_warnings;
55 fold_undefer_and_ignore_overflow_warnings ();
59 /* Try to fold ARRAY_REF ary[index] if possible and not handled by
60 normal fold, return NULL_TREE otherwise. */
63 c_fold_array_ref (tree type, tree ary, tree index)
65 if (TREE_CODE (ary) != STRING_CST
66 || TREE_CODE (index) != INTEGER_CST
67 || TREE_OVERFLOW (index)
68 || TREE_CODE (TREE_TYPE (ary)) != ARRAY_TYPE
69 || !tree_fits_uhwi_p (index))
72 tree elem_type = TREE_TYPE (TREE_TYPE (ary));
73 unsigned elem_nchars = (TYPE_PRECISION (elem_type)
74 / TYPE_PRECISION (char_type_node));
75 unsigned len = (unsigned) TREE_STRING_LENGTH (ary) / elem_nchars;
76 tree nelts = array_type_nelts (TREE_TYPE (ary));
77 bool dummy1 = true, dummy2 = true;
78 nelts = c_fully_fold_internal (nelts, true, &dummy1, &dummy2, false, false);
79 unsigned HOST_WIDE_INT i = tree_to_uhwi (index);
80 if (!tree_int_cst_le (index, nelts)
82 || i + elem_nchars > len)
86 return build_int_cst (type, TREE_STRING_POINTER (ary)[i]);
88 const unsigned char *ptr
89 = ((const unsigned char *)TREE_STRING_POINTER (ary) + i * elem_nchars);
90 return native_interpret_expr (type, ptr, elem_nchars);
93 /* Fully fold EXPR, an expression that was not folded (beyond integer
94 constant expressions and null pointer constants) when being built
95 up. If IN_INIT, this is in a static initializer and certain
96 changes are made to the folding done. Clear *MAYBE_CONST if
97 MAYBE_CONST is not NULL and EXPR is definitely not a constant
98 expression because it contains an evaluated operator (in C99) or an
99 operator outside of sizeof returning an integer constant (in C90)
100 not permitted in constant expressions, or because it contains an
101 evaluated arithmetic overflow. (*MAYBE_CONST should typically be
102 set to true by callers before calling this function.) Return the
103 folded expression. Function arguments have already been folded
104 before calling this function, as have the contents of SAVE_EXPR,
105 TARGET_EXPR, BIND_EXPR, VA_ARG_EXPR, OBJ_TYPE_REF and
106 C_MAYBE_CONST_EXPR. LVAL is true if it should be treated as an
110 c_fully_fold (tree expr, bool in_init, bool *maybe_const, bool lval)
113 tree eptype = NULL_TREE;
115 bool maybe_const_itself = true;
116 location_t loc = EXPR_LOCATION (expr);
119 maybe_const = &dummy;
120 if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
122 eptype = TREE_TYPE (expr);
123 expr = TREE_OPERAND (expr, 0);
125 ret = c_fully_fold_internal (expr, in_init, maybe_const,
126 &maybe_const_itself, false, lval);
128 ret = fold_convert_loc (loc, eptype, ret);
129 *maybe_const &= maybe_const_itself;
133 /* Internal helper for c_fully_fold. EXPR and IN_INIT are as for
134 c_fully_fold. *MAYBE_CONST_OPERANDS is cleared because of operands
135 not permitted, while *MAYBE_CONST_ITSELF is cleared because of
136 arithmetic overflow (for C90, *MAYBE_CONST_OPERANDS is carried from
137 both evaluated and unevaluated subexpressions while
138 *MAYBE_CONST_ITSELF is carried from only evaluated
139 subexpressions). FOR_INT_CONST indicates if EXPR is an expression
140 with integer constant operands, and if any of the operands doesn't
141 get folded to an integer constant, don't fold the expression itself.
142 LVAL indicates folding of lvalue, where we can't replace it with
146 c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
147 bool *maybe_const_itself, bool for_int_const, bool lval)
150 enum tree_code code = TREE_CODE (expr);
151 enum tree_code_class kind = TREE_CODE_CLASS (code);
152 location_t loc = EXPR_LOCATION (expr);
153 tree op0, op1, op2, op3;
154 tree orig_op0, orig_op1, orig_op2;
155 bool op0_const = true, op1_const = true, op2_const = true;
156 bool op0_const_self = true, op1_const_self = true, op2_const_self = true;
157 bool nowarning = TREE_NO_WARNING (expr);
159 bool op0_lval = false;
160 source_range old_range;
162 /* Constants, declarations, statements, errors, and anything else not
163 counted as an expression cannot usefully be folded further at this
165 if (!IS_EXPR_CODE_CLASS (kind) || kind == tcc_statement)
167 /* Except for variables which we can optimize to its initializer. */
168 if (VAR_P (expr) && !lval && (optimize || in_init))
171 ret = decl_constant_value_1 (expr);
173 ret = decl_constant_value (expr);
174 /* Avoid unwanted tree sharing between the initializer and current
175 function's body where the tree can be modified e.g. by the
177 if (ret != expr && TREE_STATIC (expr))
178 ret = unshare_expr (ret);
184 if (IS_EXPR_CODE_CLASS (kind))
185 old_range = EXPR_LOCATION_RANGE (expr);
187 /* Operands of variable-length expressions (function calls) have
188 already been folded, as have __builtin_* function calls, and such
189 expressions cannot occur in constant expressions. */
190 if (kind == tcc_vl_exp)
192 *maybe_const_operands = false;
197 if (code == C_MAYBE_CONST_EXPR)
199 tree pre = C_MAYBE_CONST_EXPR_PRE (expr);
200 tree inner = C_MAYBE_CONST_EXPR_EXPR (expr);
201 if (C_MAYBE_CONST_EXPR_NON_CONST (expr))
202 *maybe_const_operands = false;
203 if (C_MAYBE_CONST_EXPR_INT_OPERANDS (expr))
205 *maybe_const_itself = false;
206 inner = c_fully_fold_internal (inner, in_init, maybe_const_operands,
207 maybe_const_itself, true, lval);
210 ret = build2 (COMPOUND_EXPR, TREE_TYPE (expr), pre, inner);
216 /* Assignment, increment, decrement, function call and comma
217 operators, and statement expressions, cannot occur in constant
218 expressions if evaluated / outside of sizeof. (Function calls
219 were handled above, though VA_ARG_EXPR is treated like a function
220 call here, and statement expressions are handled through
221 C_MAYBE_CONST_EXPR to avoid folding inside them.) */
225 case PREDECREMENT_EXPR:
226 case PREINCREMENT_EXPR:
227 case POSTDECREMENT_EXPR:
228 case POSTINCREMENT_EXPR:
230 *maybe_const_operands = false;
237 *maybe_const_operands = false;
245 /* Fold individual tree codes as appropriate. */
248 case COMPOUND_LITERAL_EXPR:
249 /* Any non-constancy will have been marked in a containing
250 C_MAYBE_CONST_EXPR; there is no more folding to do here. */
254 orig_op0 = op0 = TREE_OPERAND (expr, 0);
255 op1 = TREE_OPERAND (expr, 1);
256 op2 = TREE_OPERAND (expr, 2);
257 op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
258 maybe_const_itself, for_int_const, lval);
259 STRIP_TYPE_NOPS (op0);
261 ret = build3 (COMPONENT_REF, TREE_TYPE (expr), op0, op1, op2);
264 TREE_READONLY (ret) = TREE_READONLY (expr);
265 TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
270 orig_op0 = op0 = TREE_OPERAND (expr, 0);
271 orig_op1 = op1 = TREE_OPERAND (expr, 1);
272 op2 = TREE_OPERAND (expr, 2);
273 op3 = TREE_OPERAND (expr, 3);
274 op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
275 maybe_const_itself, for_int_const, lval);
276 STRIP_TYPE_NOPS (op0);
277 op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
278 maybe_const_itself, for_int_const, false);
279 STRIP_TYPE_NOPS (op1);
280 /* Fold "foo"[2] in initializers. */
281 if (!lval && in_init)
283 ret = c_fold_array_ref (TREE_TYPE (expr), op0, op1);
288 if (op0 != orig_op0 || op1 != orig_op1)
289 ret = build4 (ARRAY_REF, TREE_TYPE (expr), op0, op1, op2, op3);
292 TREE_READONLY (ret) = TREE_READONLY (expr);
293 TREE_SIDE_EFFECTS (ret) = TREE_SIDE_EFFECTS (expr);
294 TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
301 case PREDECREMENT_EXPR:
302 case PREINCREMENT_EXPR:
303 case POSTDECREMENT_EXPR:
304 case POSTINCREMENT_EXPR:
311 case POINTER_PLUS_EXPR:
312 case POINTER_DIFF_EXPR:
341 /* Binary operations evaluating both arguments (increment and
342 decrement are binary internally in GCC). */
343 orig_op0 = op0 = TREE_OPERAND (expr, 0);
344 orig_op1 = op1 = TREE_OPERAND (expr, 1);
345 op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
346 maybe_const_itself, for_int_const,
348 STRIP_TYPE_NOPS (op0);
349 /* The RHS of a MODIFY_EXPR was fully folded when building that
350 expression for the sake of conversion warnings. */
351 if (code != MODIFY_EXPR)
352 op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
353 maybe_const_itself, for_int_const, false);
354 STRIP_TYPE_NOPS (op1);
356 if (for_int_const && (TREE_CODE (op0) != INTEGER_CST
357 || TREE_CODE (op1) != INTEGER_CST))
360 if (op0 != orig_op0 || op1 != orig_op1 || in_init)
362 ? fold_build2_initializer_loc (loc, code, TREE_TYPE (expr), op0, op1)
363 : fold_build2_loc (loc, code, TREE_TYPE (expr), op0, op1);
366 if (TREE_OVERFLOW_P (ret)
367 && !TREE_OVERFLOW_P (op0)
368 && !TREE_OVERFLOW_P (op1))
369 overflow_warning (EXPR_LOC_OR_LOC (expr, input_location), ret, expr);
370 if (code == LSHIFT_EXPR
371 && TREE_CODE (orig_op0) != INTEGER_CST
372 && TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
373 && TREE_CODE (op0) == INTEGER_CST
374 && c_inhibit_evaluation_warnings == 0
375 && tree_int_cst_sgn (op0) < 0)
376 warning_at (loc, OPT_Wshift_negative_value,
377 "left shift of negative value");
378 if ((code == LSHIFT_EXPR || code == RSHIFT_EXPR)
379 && TREE_CODE (orig_op1) != INTEGER_CST
380 && TREE_CODE (op1) == INTEGER_CST
381 && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE
382 && c_inhibit_evaluation_warnings == 0)
384 if (tree_int_cst_sgn (op1) < 0)
385 warning_at (loc, OPT_Wshift_count_negative,
387 ? G_("left shift count is negative")
388 : G_("right shift count is negative")));
389 else if ((TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
390 || TREE_CODE (TREE_TYPE (orig_op0)) == FIXED_POINT_TYPE)
391 && compare_tree_int (op1,
392 TYPE_PRECISION (TREE_TYPE (orig_op0)))
394 warning_at (loc, OPT_Wshift_count_overflow,
396 ? G_("left shift count >= width of type")
397 : G_("right shift count >= width of type")));
398 else if (TREE_CODE (TREE_TYPE (orig_op0)) == VECTOR_TYPE
399 && compare_tree_int (op1,
400 TYPE_PRECISION (TREE_TYPE (TREE_TYPE (orig_op0))))
402 warning_at (loc, OPT_Wshift_count_overflow,
404 ? G_("left shift count >= width of vector element")
405 : G_("right shift count >= width of vector element"));
407 if (code == LSHIFT_EXPR
408 /* If either OP0 has been folded to INTEGER_CST... */
409 && ((TREE_CODE (orig_op0) != INTEGER_CST
410 && TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
411 && TREE_CODE (op0) == INTEGER_CST)
412 /* ...or if OP1 has been folded to INTEGER_CST... */
413 || (TREE_CODE (orig_op1) != INTEGER_CST
414 && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE
415 && TREE_CODE (op1) == INTEGER_CST))
416 && c_inhibit_evaluation_warnings == 0)
417 /* ...then maybe we can detect an overflow. */
418 maybe_warn_shift_overflow (loc, op0, op1);
419 if ((code == TRUNC_DIV_EXPR
420 || code == CEIL_DIV_EXPR
421 || code == FLOOR_DIV_EXPR
422 || code == EXACT_DIV_EXPR
423 || code == TRUNC_MOD_EXPR)
424 && TREE_CODE (orig_op1) != INTEGER_CST
425 && TREE_CODE (op1) == INTEGER_CST
426 && (TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
427 || TREE_CODE (TREE_TYPE (orig_op0)) == FIXED_POINT_TYPE)
428 && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE)
429 warn_for_div_by_zero (loc, op1);
443 case ADDR_SPACE_CONVERT_EXPR:
444 case VIEW_CONVERT_EXPR:
445 case NON_LVALUE_EXPR:
451 /* Unary operations. */
452 orig_op0 = op0 = TREE_OPERAND (expr, 0);
453 op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
454 maybe_const_itself, for_int_const,
456 STRIP_TYPE_NOPS (op0);
458 if (for_int_const && TREE_CODE (op0) != INTEGER_CST)
461 /* ??? Cope with user tricks that amount to offsetof. The middle-end is
462 not prepared to deal with them if they occur in initializers. */
465 && (op1 = get_base_address (op0)) != NULL_TREE
466 && INDIRECT_REF_P (op1)
467 && TREE_CONSTANT (TREE_OPERAND (op1, 0)))
468 ret = fold_convert_loc (loc, TREE_TYPE (expr), fold_offsetof_1 (op0));
469 else if (op0 != orig_op0 || in_init)
471 ? fold_build1_initializer_loc (loc, code, TREE_TYPE (expr), op0)
472 : fold_build1_loc (loc, code, TREE_TYPE (expr), op0);
475 if (code == INDIRECT_REF
477 && INDIRECT_REF_P (ret))
479 TREE_READONLY (ret) = TREE_READONLY (expr);
480 TREE_SIDE_EFFECTS (ret) = TREE_SIDE_EFFECTS (expr);
481 TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
488 /* Don't warn about explicit conversions. We will already
489 have warned about suspect implicit conversions. */
493 if (TREE_OVERFLOW_P (ret) && !TREE_OVERFLOW_P (op0))
494 overflow_warning (EXPR_LOCATION (expr), ret, op0);
499 case TRUTH_ANDIF_EXPR:
500 case TRUTH_ORIF_EXPR:
501 /* Binary operations not necessarily evaluating both
503 orig_op0 = op0 = TREE_OPERAND (expr, 0);
504 orig_op1 = op1 = TREE_OPERAND (expr, 1);
505 op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self,
506 for_int_const, false);
507 STRIP_TYPE_NOPS (op0);
509 unused_p = (op0 == (code == TRUTH_ANDIF_EXPR
510 ? truthvalue_false_node
511 : truthvalue_true_node));
512 c_disable_warnings (unused_p);
513 op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self,
514 for_int_const, false);
515 STRIP_TYPE_NOPS (op1);
516 c_enable_warnings (unused_p);
519 && (TREE_CODE (op0) != INTEGER_CST
520 /* Require OP1 be an INTEGER_CST only if it's evaluated. */
521 || (!unused_p && TREE_CODE (op1) != INTEGER_CST)))
524 if (op0 != orig_op0 || op1 != orig_op1 || in_init)
526 ? fold_build2_initializer_loc (loc, code, TREE_TYPE (expr), op0, op1)
527 : fold_build2_loc (loc, code, TREE_TYPE (expr), op0, op1);
530 *maybe_const_operands &= op0_const;
531 *maybe_const_itself &= op0_const_self;
535 && (code == TRUTH_ANDIF_EXPR
536 ? op0 == truthvalue_false_node
537 : op0 == truthvalue_true_node)))
538 *maybe_const_operands &= op1_const;
541 && (code == TRUTH_ANDIF_EXPR
542 ? op0 == truthvalue_false_node
543 : op0 == truthvalue_true_node)))
544 *maybe_const_itself &= op1_const_self;
548 orig_op0 = op0 = TREE_OPERAND (expr, 0);
549 orig_op1 = op1 = TREE_OPERAND (expr, 1);
550 orig_op2 = op2 = TREE_OPERAND (expr, 2);
551 op0 = c_fully_fold_internal (op0, in_init, &op0_const, &op0_const_self,
552 for_int_const, false);
554 STRIP_TYPE_NOPS (op0);
555 c_disable_warnings (op0 == truthvalue_false_node);
556 op1 = c_fully_fold_internal (op1, in_init, &op1_const, &op1_const_self,
557 for_int_const, false);
558 STRIP_TYPE_NOPS (op1);
559 c_enable_warnings (op0 == truthvalue_false_node);
561 c_disable_warnings (op0 == truthvalue_true_node);
562 op2 = c_fully_fold_internal (op2, in_init, &op2_const, &op2_const_self,
563 for_int_const, false);
564 STRIP_TYPE_NOPS (op2);
565 c_enable_warnings (op0 == truthvalue_true_node);
568 && (TREE_CODE (op0) != INTEGER_CST
569 /* Only the evaluated operand must be an INTEGER_CST. */
570 || (op0 == truthvalue_true_node
571 ? TREE_CODE (op1) != INTEGER_CST
572 : TREE_CODE (op2) != INTEGER_CST)))
575 if (op0 != orig_op0 || op1 != orig_op1 || op2 != orig_op2)
576 ret = fold_build3_loc (loc, code, TREE_TYPE (expr), op0, op1, op2);
579 *maybe_const_operands &= op0_const;
580 *maybe_const_itself &= op0_const_self;
584 && op0 == truthvalue_false_node))
585 *maybe_const_operands &= op1_const;
588 && op0 == truthvalue_false_node))
589 *maybe_const_itself &= op1_const_self;
593 && op0 == truthvalue_true_node))
594 *maybe_const_operands &= op2_const;
597 && op0 == truthvalue_true_node))
598 *maybe_const_itself &= op2_const_self;
602 orig_op0 = op0 = TREE_OPERAND (expr, 0);
603 orig_op1 = op1 = TREE_OPERAND (expr, 1);
604 orig_op2 = op2 = TREE_OPERAND (expr, 2);
605 op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
606 maybe_const_itself, for_int_const, false);
607 STRIP_TYPE_NOPS (op0);
608 op1 = c_fully_fold_internal (op1, in_init, maybe_const_operands,
609 maybe_const_itself, for_int_const, false);
610 STRIP_TYPE_NOPS (op1);
611 op2 = c_fully_fold_internal (op2, in_init, maybe_const_operands,
612 maybe_const_itself, for_int_const, false);
613 STRIP_TYPE_NOPS (op2);
615 if (op0 != orig_op0 || op1 != orig_op1 || op2 != orig_op2)
616 ret = fold_build3_loc (loc, code, TREE_TYPE (expr), op0, op1, op2);
621 case EXCESS_PRECISION_EXPR:
622 /* Each case where an operand with excess precision may be
623 encountered must remove the EXCESS_PRECISION_EXPR around
624 inner operands and possibly put one around the whole
625 expression or possibly convert to the semantic type (which
626 c_fully_fold does); we cannot tell at this stage which is
627 appropriate in any particular case. */
631 /* Make sure to fold the contents of a SAVE_EXPR exactly once. */
632 op0 = TREE_OPERAND (expr, 0);
633 if (!SAVE_EXPR_FOLDED_P (expr))
635 op0 = c_fully_fold_internal (op0, in_init, maybe_const_operands,
636 maybe_const_itself, for_int_const,
638 TREE_OPERAND (expr, 0) = op0;
639 SAVE_EXPR_FOLDED_P (expr) = true;
641 /* Return the SAVE_EXPR operand if it is invariant. */
642 if (tree_invariant_p (op0))
647 /* Various codes may appear through folding built-in functions
648 and their arguments. */
653 /* Some folding may introduce NON_LVALUE_EXPRs; all lvalue checks
654 have been done by this point, so remove them again. */
655 nowarning |= TREE_NO_WARNING (ret);
656 STRIP_TYPE_NOPS (ret);
657 if (nowarning && !TREE_NO_WARNING (ret))
659 if (!CAN_HAVE_LOCATION_P (ret))
660 ret = build1 (NOP_EXPR, TREE_TYPE (ret), ret);
661 TREE_NO_WARNING (ret) = 1;
665 protected_set_expr_location (ret, loc);
666 if (IS_EXPR_CODE_CLASS (kind))
667 set_source_range (ret, old_range.m_start, old_range.m_finish);