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diff --git a/share/doc/gccint/Defining-Predicates.html b/share/doc/gccint/Defining-Predicates.html new file mode 100644 index 0000000..134fb3c --- /dev/null +++ b/share/doc/gccint/Defining-Predicates.html @@ -0,0 +1,227 @@ +<!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). 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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: Defining Predicates</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Defining Predicates"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Defining Predicates"> +<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="Predicates.html#Predicates" rel="up" title="Predicates"> +<link href="Constraints.html#Constraints" rel="next" title="Constraints"> +<link href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates" rel="previous" title="Machine-Independent Predicates"> +<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="Defining-Predicates"></a> +<div class="header"> +<p> +Previous: <a href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates" accesskey="p" rel="previous">Machine-Independent Predicates</a>, Up: <a href="Predicates.html#Predicates" accesskey="u" rel="up">Predicates</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="Defining-Machine_002dSpecific-Predicates"></a> +<h4 class="subsection">17.7.2 Defining Machine-Specific Predicates</h4> +<a name="index-defining-predicates"></a> +<a name="index-define_005fpredicate"></a> +<a name="index-define_005fspecial_005fpredicate"></a> + +<p>Many machines have requirements for their operands that cannot be +expressed precisely using the generic predicates. You can define +additional predicates using <code>define_predicate</code> and +<code>define_special_predicate</code> expressions. These expressions have +three operands: +</p> +<ul> +<li> The name of the predicate, as it will be referred to in +<code>match_operand</code> or <code>match_operator</code> expressions. + +</li><li> An RTL expression which evaluates to true if the predicate allows the +operand <var>op</var>, false if it does not. This expression can only use +the following RTL codes: + +<dl compact="compact"> +<dt><code>MATCH_OPERAND</code></dt> +<dd><p>When written inside a predicate expression, a <code>MATCH_OPERAND</code> +expression evaluates to true if the predicate it names would allow +<var>op</var>. The operand number and constraint are ignored. Due to +limitations in <code>genrecog</code>, you can only refer to generic +predicates and predicates that have already been defined. +</p> +</dd> +<dt><code>MATCH_CODE</code></dt> +<dd><p>This expression evaluates to true if <var>op</var> or a specified +subexpression of <var>op</var> has one of a given list of RTX codes. +</p> +<p>The first operand of this expression is a string constant containing a +comma-separated list of RTX code names (in lower case). These are the +codes for which the <code>MATCH_CODE</code> will be true. +</p> +<p>The second operand is a string constant which indicates what +subexpression of <var>op</var> to examine. If it is absent or the empty +string, <var>op</var> itself is examined. Otherwise, the string constant +must be a sequence of digits and/or lowercase letters. Each character +indicates a subexpression to extract from the current expression; for +the first character this is <var>op</var>, for the second and subsequent +characters it is the result of the previous character. A digit +<var>n</var> extracts ‘<samp>XEXP (<var>e</var>, <var>n</var>)<!-- /@w --></samp>’; a letter <var>l</var> +extracts ‘<samp>XVECEXP (<var>e</var>, 0, <var>n</var>)<!-- /@w --></samp>’ where <var>n</var> is the +alphabetic ordinal of <var>l</var> (0 for ‘a’, 1 for ’b’, and so on). The +<code>MATCH_CODE</code> then examines the RTX code of the subexpression +extracted by the complete string. It is not possible to extract +components of an <code>rtvec</code> that is not at position 0 within its RTX +object. +</p> +</dd> +<dt><code>MATCH_TEST</code></dt> +<dd><p>This expression has one operand, a string constant containing a C +expression. The predicate’s arguments, <var>op</var> and <var>mode</var>, are +available with those names in the C expression. The <code>MATCH_TEST</code> +evaluates to true if the C expression evaluates to a nonzero value. +<code>MATCH_TEST</code> expressions must not have side effects. +</p> +</dd> +<dt><code>AND</code></dt> +<dt><code>IOR</code></dt> +<dt><code>NOT</code></dt> +<dt><code>IF_THEN_ELSE</code></dt> +<dd><p>The basic ‘<samp>MATCH_</samp>’ expressions can be combined using these +logical operators, which have the semantics of the C operators +‘<samp>&&</samp>’, ‘<samp>||</samp>’, ‘<samp>!</samp>’, and ‘<samp>? :<!-- /@w --></samp>’ respectively. As +in Common Lisp, you may give an <code>AND</code> or <code>IOR</code> expression an +arbitrary number of arguments; this has exactly the same effect as +writing a chain of two-argument <code>AND</code> or <code>IOR</code> expressions. +</p></dd> +</dl> + +</li><li> An optional block of C code, which should execute +‘<samp>return true<!-- /@w --></samp>’ if the predicate is found to match and +‘<samp>return false<!-- /@w --></samp>’ if it does not. It must not have any side +effects. The predicate arguments, <var>op</var> and <var>mode</var>, are +available with those names. + +<p>If a code block is present in a predicate definition, then the RTL +expression must evaluate to true <em>and</em> the code block must +execute ‘<samp>return true<!-- /@w --></samp>’ for the predicate to allow the operand. +The RTL expression is evaluated first; do not re-check anything in the +code block that was checked in the RTL expression. +</p></li></ul> + +<p>The program <code>genrecog</code> scans <code>define_predicate</code> and +<code>define_special_predicate</code> expressions to determine which RTX +codes are possibly allowed. You should always make this explicit in +the RTL predicate expression, using <code>MATCH_OPERAND</code> and +<code>MATCH_CODE</code>. +</p> +<p>Here is an example of a simple predicate definition, from the IA64 +machine description: +</p> +<div class="smallexample"> +<pre class="smallexample">;; <span class="roman">True if <var>op</var> is a <code>SYMBOL_REF</code> which refers to the sdata section.</span> +(define_predicate "small_addr_symbolic_operand" + (and (match_code "symbol_ref") + (match_test "SYMBOL_REF_SMALL_ADDR_P (op)"))) +</pre></div> + +<p>And here is another, showing the use of the C block. +</p> +<div class="smallexample"> +<pre class="smallexample">;; <span class="roman">True if <var>op</var> is a register operand that is (or could be) a GR reg.</span> +(define_predicate "gr_register_operand" + (match_operand 0 "register_operand") +{ + unsigned int regno; + if (GET_CODE (op) == SUBREG) + op = SUBREG_REG (op); + + regno = REGNO (op); + return (regno >= FIRST_PSEUDO_REGISTER || GENERAL_REGNO_P (regno)); +}) +</pre></div> + +<p>Predicates written with <code>define_predicate</code> automatically include +a test that <var>mode</var> is <code>VOIDmode</code>, or <var>op</var> has the same +mode as <var>mode</var>, or <var>op</var> is a <code>CONST_INT</code> or +<code>CONST_DOUBLE</code>. They do <em>not</em> check specifically for +integer <code>CONST_DOUBLE</code>, nor do they test that the value of either +kind of constant fits in the requested mode. This is because +target-specific predicates that take constants usually have to do more +stringent value checks anyway. If you need the exact same treatment +of <code>CONST_INT</code> or <code>CONST_DOUBLE</code> that the generic predicates +provide, use a <code>MATCH_OPERAND</code> subexpression to call +<code>const_int_operand</code>, <code>const_double_operand</code>, or +<code>immediate_operand</code>. +</p> +<p>Predicates written with <code>define_special_predicate</code> do not get any +automatic mode checks, and are treated as having special mode handling +by <code>genrecog</code>. +</p> +<p>The program <code>genpreds</code> is responsible for generating code to +test predicates. It also writes a header file containing function +declarations for all machine-specific predicates. It is not necessary +to declare these predicates in <samp><var>cpu</var>-protos.h</samp>. +</p> +<hr> +<div class="header"> +<p> +Previous: <a href="Machine_002dIndependent-Predicates.html#Machine_002dIndependent-Predicates" accesskey="p" rel="previous">Machine-Independent Predicates</a>, Up: <a href="Predicates.html#Predicates" accesskey="u" rel="up">Predicates</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> |