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