| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being "Funding Free Software", the Front-Cover |
| Texts being (a) (see below), and with the Back-Cover Texts being (b) |
| (see below). A copy of the license is included in the section entitled |
| "GNU Free Documentation License". |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>GNU Compiler Collection (GCC) Internals: RTL Objects</title> |
| |
| <meta name="description" content="GNU Compiler Collection (GCC) Internals: RTL Objects"> |
| <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: RTL Objects"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="RTL.html#RTL" rel="up" title="RTL"> |
| <link href="RTL-Classes.html#RTL-Classes" rel="next" title="RTL Classes"> |
| <link href="RTL.html#RTL" rel="prev" title="RTL"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="RTL-Objects"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="RTL-Classes.html#RTL-Classes" accesskey="n" rel="next">RTL Classes</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="RTL-Object-Types"></a> |
| <h3 class="section">13.1 RTL Object Types</h3> |
| <a name="index-RTL-object-types"></a> |
| |
| <a name="index-RTL-integers"></a> |
| <a name="index-RTL-strings"></a> |
| <a name="index-RTL-vectors"></a> |
| <a name="index-RTL-expression"></a> |
| <a name="index-RTX-_0028See-RTL_0029"></a> |
| <p>RTL uses five kinds of objects: expressions, integers, wide integers, |
| strings and vectors. Expressions are the most important ones. An RTL |
| expression (“RTX”, for short) is a C structure, but it is usually |
| referred to with a pointer; a type that is given the typedef name |
| <code>rtx</code>. |
| </p> |
| <p>An integer is simply an <code>int</code>; their written form uses decimal |
| digits. A wide integer is an integral object whose type is |
| <code>HOST_WIDE_INT</code>; their written form uses decimal digits. |
| </p> |
| <p>A string is a sequence of characters. In core it is represented as a |
| <code>char *</code> in usual C fashion, and it is written in C syntax as well. |
| However, strings in RTL may never be null. If you write an empty string in |
| a machine description, it is represented in core as a null pointer rather |
| than as a pointer to a null character. In certain contexts, these null |
| pointers instead of strings are valid. Within RTL code, strings are most |
| commonly found inside <code>symbol_ref</code> expressions, but they appear in |
| other contexts in the RTL expressions that make up machine descriptions. |
| </p> |
| <p>In a machine description, strings are normally written with double |
| quotes, as you would in C. However, strings in machine descriptions may |
| extend over many lines, which is invalid C, and adjacent string |
| constants are not concatenated as they are in C. Any string constant |
| may be surrounded with a single set of parentheses. Sometimes this |
| makes the machine description easier to read. |
| </p> |
| <p>There is also a special syntax for strings, which can be useful when C |
| code is embedded in a machine description. Wherever a string can |
| appear, it is also valid to write a C-style brace block. The entire |
| brace block, including the outermost pair of braces, is considered to be |
| the string constant. Double quote characters inside the braces are not |
| special. Therefore, if you write string constants in the C code, you |
| need not escape each quote character with a backslash. |
| </p> |
| <p>A vector contains an arbitrary number of pointers to expressions. The |
| number of elements in the vector is explicitly present in the vector. |
| The written form of a vector consists of square brackets |
| (‘<samp>[…]</samp>’) surrounding the elements, in sequence and with |
| whitespace separating them. Vectors of length zero are not created; |
| null pointers are used instead. |
| </p> |
| <a name="index-expression-codes"></a> |
| <a name="index-codes_002c-RTL-expression"></a> |
| <a name="index-GET_005fCODE"></a> |
| <a name="index-PUT_005fCODE"></a> |
| <p>Expressions are classified by <em>expression codes</em> (also called RTX |
| codes). The expression code is a name defined in <samp>rtl.def</samp>, which is |
| also (in uppercase) a C enumeration constant. The possible expression |
| codes and their meanings are machine-independent. The code of an RTX can |
| be extracted with the macro <code>GET_CODE (<var>x</var>)</code> and altered with |
| <code>PUT_CODE (<var>x</var>, <var>newcode</var>)</code>. |
| </p> |
| <p>The expression code determines how many operands the expression contains, |
| and what kinds of objects they are. In RTL, unlike Lisp, you cannot tell |
| by looking at an operand what kind of object it is. Instead, you must know |
| from its context—from the expression code of the containing expression. |
| For example, in an expression of code <code>subreg</code>, the first operand is |
| to be regarded as an expression and the second operand as an integer. In |
| an expression of code <code>plus</code>, there are two operands, both of which |
| are to be regarded as expressions. In a <code>symbol_ref</code> expression, |
| there is one operand, which is to be regarded as a string. |
| </p> |
| <p>Expressions are written as parentheses containing the name of the |
| expression type, its flags and machine mode if any, and then the operands |
| of the expression (separated by spaces). |
| </p> |
| <p>Expression code names in the ‘<samp>md</samp>’ file are written in lowercase, |
| but when they appear in C code they are written in uppercase. In this |
| manual, they are shown as follows: <code>const_int</code>. |
| </p> |
| <a name="index-_0028nil_0029"></a> |
| <a name="index-nil"></a> |
| <p>In a few contexts a null pointer is valid where an expression is normally |
| wanted. The written form of this is <code>(nil)</code>. |
| </p> |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="RTL-Classes.html#RTL-Classes" accesskey="n" rel="next">RTL Classes</a>, Up: <a href="RTL.html#RTL" accesskey="u" rel="up">RTL</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
