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diff --git a/share/doc/gccint/Conditional-Execution.html b/share/doc/gccint/Conditional-Execution.html new file mode 100644 index 0000000..27011ed --- /dev/null +++ b/share/doc/gccint/Conditional-Execution.html @@ -0,0 +1,176 @@ +<!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: Conditional Execution</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Conditional Execution"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Conditional Execution"> +<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="Define-Subst.html#Define-Subst" rel="next" title="Define Subst"> +<link href="Processor-pipeline-description.html#Processor-pipeline-description" rel="previous" title="Processor pipeline description"> +<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="Conditional-Execution"></a> +<div class="header"> +<p> +Next: <a href="Define-Subst.html#Define-Subst" accesskey="n" rel="next">Define Subst</a>, Previous: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="p" rel="previous">Insn Attributes</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="Conditional-Execution-1"></a> +<h3 class="section">17.20 Conditional Execution</h3> +<a name="index-conditional-execution"></a> +<a name="index-predication"></a> + +<p>A number of architectures provide for some form of conditional +execution, or predication. The hallmark of this feature is the +ability to nullify most of the instructions in the instruction set. +When the instruction set is large and not entirely symmetric, it +can be quite tedious to describe these forms directly in the +<samp>.md</samp> file. An alternative is the <code>define_cond_exec</code> template. +</p> +<a name="index-define_005fcond_005fexec"></a> +<div class="smallexample"> +<pre class="smallexample">(define_cond_exec + [<var>predicate-pattern</var>] + "<var>condition</var>" + "<var>output-template</var>" + "<var>optional-insn-attribues</var>") +</pre></div> + +<p><var>predicate-pattern</var> is the condition that must be true for the +insn to be executed at runtime and should match a relational operator. +One can use <code>match_operator</code> to match several relational operators +at once. Any <code>match_operand</code> operands must have no more than one +alternative. +</p> +<p><var>condition</var> is a C expression that must be true for the generated +pattern to match. +</p> +<a name="index-current_005finsn_005fpredicate"></a> +<p><var>output-template</var> is a string similar to the <code>define_insn</code> +output template (see <a href="Output-Template.html#Output-Template">Output Template</a>), except that the ‘<samp>*</samp>’ +and ‘<samp>@</samp>’ special cases do not apply. This is only useful if the +assembly text for the predicate is a simple prefix to the main insn. +In order to handle the general case, there is a global variable +<code>current_insn_predicate</code> that will contain the entire predicate +if the current insn is predicated, and will otherwise be <code>NULL</code>. +</p> +<p><var>optional-insn-attributes</var> is an optional vector of attributes that gets +appended to the insn attributes of the produced cond_exec rtx. It can +be used to add some distinguishing attribute to cond_exec rtxs produced +that way. An example usage would be to use this attribute in conjunction +with attributes on the main pattern to disable particular alternatives under +certain conditions. +</p> +<p>When <code>define_cond_exec</code> is used, an implicit reference to +the <code>predicable</code> instruction attribute is made. +See <a href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a>. This attribute must be a boolean (i.e. have +exactly two elements in its <var>list-of-values</var>), with the possible +values being <code>no</code> and <code>yes</code>. The default and all uses in +the insns must be a simple constant, not a complex expressions. It +may, however, depend on the alternative, by using a comma-separated +list of values. If that is the case, the port should also define an +<code>enabled</code> attribute (see <a href="Disable-Insn-Alternatives.html#Disable-Insn-Alternatives">Disable Insn Alternatives</a>), which +should also allow only <code>no</code> and <code>yes</code> as its values. +</p> +<p>For each <code>define_insn</code> for which the <code>predicable</code> +attribute is true, a new <code>define_insn</code> pattern will be +generated that matches a predicated version of the instruction. +For example, +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "addsi" + [(set (match_operand:SI 0 "register_operand" "r") + (plus:SI (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r")))] + "<var>test1</var>" + "add %2,%1,%0") + +(define_cond_exec + [(ne (match_operand:CC 0 "register_operand" "c") + (const_int 0))] + "<var>test2</var>" + "(%0)") +</pre></div> + +<p>generates a new pattern +</p> +<div class="smallexample"> +<pre class="smallexample">(define_insn "" + [(cond_exec + (ne (match_operand:CC 3 "register_operand" "c") (const_int 0)) + (set (match_operand:SI 0 "register_operand" "r") + (plus:SI (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r"))))] + "(<var>test2</var>) && (<var>test1</var>)" + "(%3) add %2,%1,%0") +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Define-Subst.html#Define-Subst" accesskey="n" rel="next">Define Subst</a>, Previous: <a href="Insn-Attributes.html#Insn-Attributes" accesskey="p" rel="previous">Insn Attributes</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> |