/* Language-level data type conversion for GNU C. Copyright (C) 1987, 1988, 1991 Free Software Foundation, Inc. This file is part of GNU CC. GNU CC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU CC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU CC; see the file COPYING. If not, write to the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ /* This file contains the functions for converting C expressions to different data types. The only entry point is `convert'. Every language front end must have a `convert' function but what kind of conversions it does will depend on the language. */ #include "config.h" #include "tree.h" #include "flags.h" /* Change of width--truncation and extension of integers or reals-- is represented with NOP_EXPR. Proper functioning of many things assumes that no other conversions can be NOP_EXPRs. Conversion between integer and pointer is represented with CONVERT_EXPR. Converting integer to real uses FLOAT_EXPR and real to integer uses FIX_TRUNC_EXPR. Here is a list of all the functions that assume that widening and narrowing is always done with a NOP_EXPR: In c-convert.c, convert_to_integer. In c-typeck.c, build_binary_op (boolean ops), and truthvalue_conversion. In expr.c: expand_expr, for operands of a MULT_EXPR. In fold-const.c: fold. In tree.c: get_narrower and get_unwidened. */ /* Subroutines of `convert'. */ static tree convert_to_pointer (type, expr) tree type, expr; { register tree intype = TREE_TYPE (expr); register enum tree_code form = TREE_CODE (intype); if (integer_zerop (expr)) { if (type == TREE_TYPE (null_pointer_node)) return null_pointer_node; expr = build_int_2 (0, 0); TREE_TYPE (expr) = type; return expr; } if (form == POINTER_TYPE) return build1 (NOP_EXPR, type, expr); if (form == INTEGER_TYPE || form == ENUMERAL_TYPE) { if (type_precision (intype) == POINTER_SIZE) return build1 (CONVERT_EXPR, type, expr); expr = convert (type_for_size (POINTER_SIZE, 0), expr); if (TYPE_MODE (TREE_TYPE (expr)) != TYPE_MODE (type)) /* There is supposed to be some integral type that is the same width as a pointer. */ abort (); return convert_to_pointer (type, expr); } error ("cannot convert to a pointer type"); return null_pointer_node; } static tree convert_to_real (type, expr) tree type, expr; { register enum tree_code form = TREE_CODE (TREE_TYPE (expr)); if (form == REAL_TYPE) return build1 (flag_float_store ? CONVERT_EXPR : NOP_EXPR, type, expr); if (form == INTEGER_TYPE || form == ENUMERAL_TYPE) return build1 (FLOAT_EXPR, type, expr); if (form == POINTER_TYPE) error ("pointer value used where a float was expected"); else error ("aggregate value used where a float was expected"); { register tree tem = make_node (REAL_CST); TREE_TYPE (tem) = type; TREE_REAL_CST (tem) = REAL_VALUE_ATOF ("0.0"); return tem; } } /* The result of this is always supposed to be a newly created tree node not in use in any existing structure. */ static tree convert_to_integer (type, expr) tree type, expr; { register tree intype = TREE_TYPE (expr); register enum tree_code form = TREE_CODE (intype); if (form == POINTER_TYPE) { if (integer_zerop (expr)) expr = integer_zero_node; else expr = fold (build1 (CONVERT_EXPR, type_for_size (POINTER_SIZE, 0), expr)); intype = TREE_TYPE (expr); form = TREE_CODE (intype); if (intype == type) return expr; } if (form == INTEGER_TYPE || form == ENUMERAL_TYPE) { register unsigned outprec = TYPE_PRECISION (type); register unsigned inprec = TYPE_PRECISION (intype); register enum tree_code ex_form = TREE_CODE (expr); /* If we are widening the type, put in an explicit conversion. Similarly if we are not changing the width. However, if this is a logical operation that just returns 0 or 1, we can change the type of the expression (see below). */ if (TREE_CODE_CLASS (ex_form) == '<' || ex_form == TRUTH_AND_EXPR || ex_form == TRUTH_ANDIF_EXPR || ex_form == TRUTH_OR_EXPR || ex_form == TRUTH_ORIF_EXPR || ex_form == TRUTH_NOT_EXPR) { TREE_TYPE (expr) = type; return expr; } else if (outprec >= inprec) return build1 (NOP_EXPR, type, expr); /* Here detect when we can distribute the truncation down past some arithmetic. For example, if adding two longs and converting to an int, we can equally well convert both to ints and then add. For the operations handled here, such truncation distribution is always safe. It is desirable in these cases: 1) when truncating down to full-word from a larger size 2) when truncating takes no work. 3) when at least one operand of the arithmetic has been extended (as by C's default conversions). In this case we need two conversions if we do the arithmetic as already requested, so we might as well truncate both and then combine. Perhaps that way we need only one. Note that in general we cannot do the arithmetic in a type shorter than the desired result of conversion, even if the operands are both extended from a shorter type, because they might overflow if combined in that type. The exceptions to this--the times when two narrow values can be combined in their narrow type even to make a wider result--are handled by "shorten" in build_binary_op. */ switch (ex_form) { case RSHIFT_EXPR: /* We can pass truncation down through right shifting when the shift count is a nonpositive constant. */ if (TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST && tree_int_cst_lt (TREE_OPERAND (expr, 1), integer_one_node)) goto trunc1; break; case LSHIFT_EXPR: /* We can pass truncation down through left shifting when the shift count is a nonnegative constant. */ if (TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST && ! tree_int_cst_lt (TREE_OPERAND (expr, 1), integer_zero_node) && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST) { /* If shift count is less than the width of the truncated type, really shift. */ if (tree_int_cst_lt (TREE_OPERAND (expr, 1), TYPE_SIZE (type))) /* In this case, shifting is like multiplication. */ goto trunc1; else /* If it is >= that width, result is zero. Handling this with trunc1 would give the wrong result: (int) ((long long) a << 32) is well defined (as 0) but (int) a << 32 is undefined and would get a warning. */ return convert_to_integer (type, integer_zero_node); } break; case MAX_EXPR: case MIN_EXPR: case MULT_EXPR: { tree arg0 = get_unwidened (TREE_OPERAND (expr, 0), type); tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type); /* Don't distribute unless the output precision is at least as big as the actual inputs. Otherwise, the comparison of the truncated values will be wrong. */ if (outprec >= TYPE_PRECISION (TREE_TYPE (arg0)) && outprec >= TYPE_PRECISION (TREE_TYPE (arg1)) /* If signedness of arg0 and arg1 don't match, we can't necessarily find a type to compare them in. */ && (TREE_UNSIGNED (TREE_TYPE (arg0)) == TREE_UNSIGNED (TREE_TYPE (arg1)))) goto trunc1; break; } case PLUS_EXPR: case MINUS_EXPR: case BIT_AND_EXPR: case BIT_IOR_EXPR: case BIT_XOR_EXPR: case BIT_ANDTC_EXPR: trunc1: { tree arg0 = get_unwidened (TREE_OPERAND (expr, 0), type); tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type); if (outprec >= BITS_PER_WORD || TRULY_NOOP_TRUNCATION (outprec, inprec) || inprec > TYPE_PRECISION (TREE_TYPE (arg0)) || inprec > TYPE_PRECISION (TREE_TYPE (arg1))) { /* Do the arithmetic in type TYPEX, then convert result to TYPE. */ register tree typex = type; /* Can't do arithmetic in enumeral types so use an integer type that will hold the values. */ if (TREE_CODE (typex) == ENUMERAL_TYPE) typex = type_for_size (TYPE_PRECISION (typex), TREE_UNSIGNED (typex)); /* But now perhaps TYPEX is as wide as INPREC. In that case, do nothing special here. (Otherwise would recurse infinitely in convert. */ if (TYPE_PRECISION (typex) != inprec) { /* Don't do unsigned arithmetic where signed was wanted, or vice versa. Exception: if either of the original operands were unsigned then can safely do the work as unsigned. And we may need to do it as unsigned if we truncate to the original size. */ typex = ((TREE_UNSIGNED (TREE_TYPE (expr)) || TREE_UNSIGNED (TREE_TYPE (arg0)) || TREE_UNSIGNED (TREE_TYPE (arg1))) ? unsigned_type (typex) : signed_type (typex)); return convert (type, build_binary_op (ex_form, convert (typex, arg0), convert (typex, arg1), 0)); } } } break; case NEGATE_EXPR: case BIT_NOT_EXPR: { register tree typex = type; /* Can't do arithmetic in enumeral types so use an integer type that will hold the values. */ if (TREE_CODE (typex) == ENUMERAL_TYPE) typex = type_for_size (TYPE_PRECISION (typex), TREE_UNSIGNED (typex)); /* But now perhaps TYPEX is as wide as INPREC. In that case, do nothing special here. (Otherwise would recurse infinitely in convert. */ if (TYPE_PRECISION (typex) != inprec) { /* Don't do unsigned arithmetic where signed was wanted, or vice versa. */ typex = (TREE_UNSIGNED (TREE_TYPE (expr)) ? unsigned_type (typex) : signed_type (typex)); return convert (type, build_unary_op (ex_form, convert (typex, TREE_OPERAND (expr, 0)), 1)); } } case NOP_EXPR: /* If truncating after truncating, might as well do all at once. If truncating after extending, we may get rid of wasted work. */ return convert (type, get_unwidened (TREE_OPERAND (expr, 0), type)); case COND_EXPR: /* Can treat the two alternative values like the operands of an arithmetic expression. */ { tree arg1 = get_unwidened (TREE_OPERAND (expr, 1), type); tree arg2 = get_unwidened (TREE_OPERAND (expr, 2), type); if (outprec >= BITS_PER_WORD || TRULY_NOOP_TRUNCATION (outprec, inprec) || inprec > TYPE_PRECISION (TREE_TYPE (arg1)) || inprec > TYPE_PRECISION (TREE_TYPE (arg2))) { /* Do the arithmetic in type TYPEX, then convert result to TYPE. */ register tree typex = type; /* Can't do arithmetic in enumeral types so use an integer type that will hold the values. */ if (TREE_CODE (typex) == ENUMERAL_TYPE) typex = type_for_size (TYPE_PRECISION (typex), TREE_UNSIGNED (typex)); /* But now perhaps TYPEX is as wide as INPREC. In that case, do nothing special here. (Otherwise would recurse infinitely in convert. */ if (TYPE_PRECISION (typex) != inprec) { /* Don't do unsigned arithmetic where signed was wanted, or vice versa. */ typex = (TREE_UNSIGNED (TREE_TYPE (expr)) ? unsigned_type (typex) : signed_type (typex)); return convert (type, fold (build (COND_EXPR, typex, TREE_OPERAND (expr, 0), convert (typex, arg1), convert (typex, arg2)))); } else /* It is sometimes worthwhile to push the narrowing down through the conditional. */ return fold (build (COND_EXPR, type, TREE_OPERAND (expr, 0), convert (type, TREE_OPERAND (expr, 1)), convert (type, TREE_OPERAND (expr, 2)))); } } } return build1 (NOP_EXPR, type, expr); } if (form == REAL_TYPE) return build1 (FIX_TRUNC_EXPR, type, expr); error ("aggregate value used where an integer was expected"); { register tree tem = build_int_2 (0, 0); TREE_TYPE (tem) = type; return tem; } } /* Create an expression whose value is that of EXPR, converted to type TYPE. The TREE_TYPE of the value is always TYPE. This function implements all reasonable conversions; callers should filter out those that are not permitted by the language being compiled. */ tree convert (type, expr) tree type, expr; { register tree e = expr; register enum tree_code code = TREE_CODE (type); if (type == TREE_TYPE (expr) || TREE_CODE (expr) == ERROR_MARK) return expr; if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (TREE_TYPE (expr))) return fold (build1 (NOP_EXPR, type, expr)); if (TREE_CODE (TREE_TYPE (expr)) == ERROR_MARK) return error_mark_node; if (TREE_CODE (TREE_TYPE (expr)) == VOID_TYPE) { error ("void value not ignored as it ought to be"); return error_mark_node; } if (code == VOID_TYPE) return build1 (CONVERT_EXPR, type, e); #if 0 /* This is incorrect. A truncation can't be stripped this way. Extensions will be stripped by the use of get_unwidened. */ if (TREE_CODE (expr) == NOP_EXPR) return convert (type, TREE_OPERAND (expr, 0)); #endif if (code == INTEGER_TYPE || code == ENUMERAL_TYPE) return fold (convert_to_integer (type, e)); if (code == POINTER_TYPE) return fold (convert_to_pointer (type, e)); if (code == REAL_TYPE) return fold (convert_to_real (type, e)); error ("conversion to non-scalar type requested"); return error_mark_node; }