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diff --git a/share/doc/gccint/Output-Statement.html b/share/doc/gccint/Output-Statement.html new file mode 100644 index 0000000..99757d9 --- /dev/null +++ b/share/doc/gccint/Output-Statement.html @@ -0,0 +1,201 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>GNU Compiler Collection (GCC) Internals: Output Statement</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Output Statement"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Output Statement"> +<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="Machine-Desc.html#Machine-Desc" rel="up" title="Machine Desc"> +<link href="Predicates.html#Predicates" rel="next" title="Predicates"> +<link href="Output-Template.html#Output-Template" rel="previous" title="Output Template"> +<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="Output-Statement"></a> +<div class="header"> +<p> +Next: <a href="Predicates.html#Predicates" accesskey="n" rel="next">Predicates</a>, Previous: <a href="Output-Template.html#Output-Template" accesskey="p" rel="previous">Output Template</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</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="C-Statements-for-Assembler-Output"></a> +<h3 class="section">17.6 C Statements for Assembler Output</h3> +<a name="index-output-statements"></a> +<a name="index-C-statements-for-assembler-output"></a> +<a name="index-generating-assembler-output"></a> + +<p>Often a single fixed template string cannot produce correct and efficient +assembler code for all the cases that are recognized by a single +instruction pattern. For example, the opcodes may depend on the kinds of +operands; or some unfortunate combinations of operands may require extra +machine instructions. +</p> +<p>If the output control string starts with a ‘<samp>@</samp>’, then it is actually +a series of templates, each on a separate line. (Blank lines and +leading spaces and tabs are ignored.) The templates correspond to the +pattern’s constraint alternatives (see <a href="Multi_002dAlternative.html#Multi_002dAlternative">Multi-Alternative</a>). For example, +if a target machine has a two-address add instruction ‘<samp>addr</samp>’ to add +into a register and another ‘<samp>addm</samp>’ to add a register to memory, you +might write this pattern: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "addsi3" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (plus:SI (match_operand:SI 1 "general_operand" "0,0") + (match_operand:SI 2 "general_operand" "g,r")))] + "" + "@ + addr %2,%0 + addm %2,%0") +</pre></div> + +<a name="index-_002a-in-template"></a> +<a name="index-asterisk-in-template"></a> +<p>If the output control string starts with a ‘<samp>*</samp>’, then it is not an +output template but rather a piece of C program that should compute a +template. It should execute a <code>return</code> statement to return the +template-string you want. Most such templates use C string literals, which +require doublequote characters to delimit them. To include these +doublequote characters in the string, prefix each one with ‘<samp>\</samp>’. +</p> +<p>If the output control string is written as a brace block instead of a +double-quoted string, it is automatically assumed to be C code. In that +case, it is not necessary to put in a leading asterisk, or to escape the +doublequotes surrounding C string literals. +</p> +<p>The operands may be found in the array <code>operands</code>, whose C data type +is <code>rtx []</code>. +</p> +<p>It is very common to select different ways of generating assembler code +based on whether an immediate operand is within a certain range. Be +careful when doing this, because the result of <code>INTVAL</code> is an +integer on the host machine. If the host machine has more bits in an +<code>int</code> than the target machine has in the mode in which the constant +will be used, then some of the bits you get from <code>INTVAL</code> will be +superfluous. For proper results, you must carefully disregard the +values of those bits. +</p> +<a name="index-output_005fasm_005finsn"></a> +<p>It is possible to output an assembler instruction and then go on to output +or compute more of them, using the subroutine <code>output_asm_insn</code>. This +receives two arguments: a template-string and a vector of operands. The +vector may be <code>operands</code>, or it may be another array of <code>rtx</code> +that you declare locally and initialize yourself. +</p> +<a name="index-which_005falternative"></a> +<p>When an insn pattern has multiple alternatives in its constraints, often +the appearance of the assembler code is determined mostly by which alternative +was matched. When this is so, the C code can test the variable +<code>which_alternative</code>, which is the ordinal number of the alternative +that was actually satisfied (0 for the first, 1 for the second alternative, +etc.). +</p> +<p>For example, suppose there are two opcodes for storing zero, ‘<samp>clrreg</samp>’ +for registers and ‘<samp>clrmem</samp>’ for memory locations. Here is how +a pattern could use <code>which_alternative</code> to choose between them: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + { + return (which_alternative == 0 + ? "clrreg %0" : "clrmem %0"); + }) +</pre></div> + +<p>The example above, where the assembler code to generate was +<em>solely</em> determined by the alternative, could also have been specified +as follows, having the output control string start with a ‘<samp>@</samp>’: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + "@ + clrreg %0 + clrmem %0") +</pre></div> + +<p>If you just need a little bit of C code in one (or a few) alternatives, +you can use ‘<samp>*</samp>’ inside of a ‘<samp>@</samp>’ multi-alternative template: +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,<,m") + (const_int 0))] + "" + "@ + clrreg %0 + * return stack_mem_p (operands[0]) ? \"push 0\" : \"clrmem %0\"; + clrmem %0") +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Predicates.html#Predicates" accesskey="n" rel="next">Predicates</a>, Previous: <a href="Output-Template.html#Output-Template" accesskey="p" rel="previous">Output Template</a>, Up: <a href="Machine-Desc.html#Machine-Desc" accesskey="u" rel="up">Machine Desc</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> |