visus
/
toolchain-gcc-arm-embedded

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2020 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 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Output Template (GNU Compiler Collection (GCC) Internals)</title>

<meta name="description" content="Output Template (GNU Compiler Collection (GCC) Internals)">
<meta name="keywords" content="Output Template (GNU Compiler Collection (GCC) Internals)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<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="Machine-Desc.html#Machine-Desc" rel="up" title="Machine Desc">
<link href="Output-Statement.html#Output-Statement" rel="next" title="Output Statement">
<link href="RTL-Template.html#RTL-Template" rel="prev" title="RTL Template">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
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.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Output-Template"></a>
<div class="header">
<p>
Next: <a href="Output-Statement.html#Output-Statement" accesskey="n" rel="next">Output Statement</a>, Previous: <a href="RTL-Template.html#RTL-Template" accesskey="p" rel="prev">RTL Template</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</a> &nbsp; [<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="Output-Templates-and-Operand-Substitution"></a>
<h3 class="section">17.5 Output Templates and Operand Substitution</h3>
<a name="index-output-templates"></a>
<a name="index-operand-substitution"></a>

<a name="index-_0025-in-template"></a>
<a name="index-percent-sign"></a>
<p>The <em>output template</em> is a string which specifies how to output the
assembler code for an instruction pattern.  Most of the template is a
fixed string which is output literally.  The character &lsquo;<samp>%</samp>&rsquo; is used
to specify where to substitute an operand; it can also be used to
identify places where different variants of the assembler require
different syntax.
</p>
<p>In the simplest case, a &lsquo;<samp>%</samp>&rsquo; followed by a digit <var>n</var> says to output
operand <var>n</var> at that point in the string.
</p>
<p>&lsquo;<samp>%</samp>&rsquo; followed by a letter and a digit says to output an operand in an
alternate fashion.  Four letters have standard, built-in meanings described
below.  The machine description macro <code>PRINT_OPERAND</code> can define
additional letters with nonstandard meanings.
</p>
<p>&lsquo;<samp>%c<var>digit</var></samp>&rsquo; can be used to substitute an operand that is a
constant value without the syntax that normally indicates an immediate
operand.
</p>
<p>&lsquo;<samp>%n<var>digit</var></samp>&rsquo; is like &lsquo;<samp>%c<var>digit</var></samp>&rsquo; except that the value of
the constant is negated before printing.
</p>
<p>&lsquo;<samp>%a<var>digit</var></samp>&rsquo; can be used to substitute an operand as if it were a
memory reference, with the actual operand treated as the address.  This may
be useful when outputting a &ldquo;load address&rdquo; instruction, because often the
assembler syntax for such an instruction requires you to write the operand
as if it were a memory reference.
</p>
<p>&lsquo;<samp>%l<var>digit</var></samp>&rsquo; is used to substitute a <code>label_ref</code> into a jump
instruction.
</p>
<p>&lsquo;<samp>%=</samp>&rsquo; outputs a number which is unique to each instruction in the
entire compilation.  This is useful for making local labels to be
referred to more than once in a single template that generates multiple
assembler instructions.
</p>
<p>&lsquo;<samp>%</samp>&rsquo; followed by a punctuation character specifies a substitution that
does not use an operand.  Only one case is standard: &lsquo;<samp>%%</samp>&rsquo; outputs a
&lsquo;<samp>%</samp>&rsquo; into the assembler code.  Other nonstandard cases can be
defined in the <code>PRINT_OPERAND</code> macro.  You must also define
which punctuation characters are valid with the
<code>PRINT_OPERAND_PUNCT_VALID_P</code> macro.
</p>
<a name="index-_005c"></a>
<a name="index-backslash"></a>
<p>The template may generate multiple assembler instructions.  Write the text
for the instructions, with &lsquo;<samp>\;</samp>&rsquo; between them.
</p>
<a name="index-matching-operands"></a>
<p>When the RTL contains two operands which are required by constraint to match
each other, the output template must refer only to the lower-numbered operand.
Matching operands are not always identical, and the rest of the compiler
arranges to put the proper RTL expression for printing into the lower-numbered
operand.
</p>
<p>One use of nonstandard letters or punctuation following &lsquo;<samp>%</samp>&rsquo; is to
distinguish between different assembler languages for the same machine; for
example, Motorola syntax versus MIT syntax for the 68000.  Motorola syntax
requires periods in most opcode names, while MIT syntax does not.  For
example, the opcode &lsquo;<samp>movel</samp>&rsquo; in MIT syntax is &lsquo;<samp>move.l</samp>&rsquo; in Motorola
syntax.  The same file of patterns is used for both kinds of output syntax,
but the character sequence &lsquo;<samp>%.</samp>&rsquo; is used in each place where Motorola
syntax wants a period.  The <code>PRINT_OPERAND</code> macro for Motorola syntax
defines the sequence to output a period; the macro for MIT syntax defines
it to do nothing.
</p>
<a name="index-_0023-in-template"></a>
<p>As a special case, a template consisting of the single character <code>#</code>
instructs the compiler to first split the insn, and then output the
resulting instructions separately.  This helps eliminate redundancy in the
output templates.   If you have a <code>define_insn</code> that needs to emit
multiple assembler instructions, and there is a matching <code>define_split</code>
already defined, then you can simply use <code>#</code> as the output template
instead of writing an output template that emits the multiple assembler
instructions.
</p>
<p>Note that <code>#</code> only has an effect while generating assembly code;
it does not affect whether a split occurs earlier.  An associated
<code>define_split</code> must exist and it must be suitable for use after
register allocation.
</p>
<p>If the macro <code>ASSEMBLER_DIALECT</code> is defined, you can use construct
of the form &lsquo;<samp>{option0|option1|option2}</samp>&rsquo; in the templates.  These
describe multiple variants of assembler language syntax.
See <a href="Instruction-Output.html#Instruction-Output">Instruction Output</a>.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Output-Statement.html#Output-Statement" accesskey="n" rel="next">Output Statement</a>, Previous: <a href="RTL-Template.html#RTL-Template" accesskey="p" rel="prev">RTL Template</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</a> &nbsp; [<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>