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diff --git a/share/doc/gccint/Comparisons.html b/share/doc/gccint/Comparisons.html new file mode 100644 index 0000000..caf533f --- /dev/null +++ b/share/doc/gccint/Comparisons.html @@ -0,0 +1,210 @@ +<!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: Comparisons</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Comparisons"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Comparisons"> +<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="Bit_002dFields.html#Bit_002dFields" rel="next" title="Bit-Fields"> +<link href="Arithmetic.html#Arithmetic" rel="previous" title="Arithmetic"> +<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="Comparisons"></a> +<div class="header"> +<p> +Next: <a href="Bit_002dFields.html#Bit_002dFields" accesskey="n" rel="next">Bit-Fields</a>, Previous: <a href="Arithmetic.html#Arithmetic" accesskey="p" rel="previous">Arithmetic</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="Comparison-Operations"></a> +<h3 class="section">14.10 Comparison Operations</h3> +<a name="index-RTL-comparison-operations"></a> + +<p>Comparison operators test a relation on two operands and are considered +to represent a machine-dependent nonzero value described by, but not +necessarily equal to, <code>STORE_FLAG_VALUE</code> (see <a href="Misc.html#Misc">Misc</a>) +if the relation holds, or zero if it does not, for comparison operators +whose results have a ‘MODE_INT’ mode, +<code>FLOAT_STORE_FLAG_VALUE</code> (see <a href="Misc.html#Misc">Misc</a>) if the relation holds, or +zero if it does not, for comparison operators that return floating-point +values, and a vector of either <code>VECTOR_STORE_FLAG_VALUE</code> (see <a href="Misc.html#Misc">Misc</a>) +if the relation holds, or of zeros if it does not, for comparison operators +that return vector results. +The mode of the comparison operation is independent of the mode +of the data being compared. If the comparison operation is being tested +(e.g., the first operand of an <code>if_then_else</code>), the mode must be +<code>VOIDmode</code>. +</p> +<a name="index-condition-codes"></a> +<p>A comparison operation compares two data +objects. The mode of the comparison is determined by the operands; they +must both be valid for a common machine mode. A comparison with both +operands constant would be invalid as the machine mode could not be +deduced from it, but such a comparison should never exist in RTL due to +constant folding. +</p> +<p>Usually only one style +of comparisons is supported on a particular machine, but the combine +pass will try to merge operations to produce code like +<code>(eq <var>x</var> <var>y</var>)</code>, +in case it exists in the context of the particular insn involved. +</p> +<p>Inequality comparisons come in two flavors, signed and unsigned. Thus, +there are distinct expression codes <code>gt</code> and <code>gtu</code> for signed and +unsigned greater-than. These can produce different results for the same +pair of integer values: for example, 1 is signed greater-than -1 but not +unsigned greater-than, because -1 when regarded as unsigned is actually +<code>0xffffffff</code> which is greater than 1. +</p> +<p>The signed comparisons are also used for floating point values. Floating +point comparisons are distinguished by the machine modes of the operands. +</p> +<dl compact="compact"> +<dd><a name="index-eq"></a> +<a name="index-equal"></a> +</dd> +<dt><code>(eq:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p><code>STORE_FLAG_VALUE</code> if the values represented by <var>x</var> and <var>y</var> +are equal, otherwise 0. +</p> +<a name="index-ne"></a> +<a name="index-not-equal"></a> +</dd> +<dt><code>(ne:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p><code>STORE_FLAG_VALUE</code> if the values represented by <var>x</var> and <var>y</var> +are not equal, otherwise 0. +</p> +<a name="index-gt"></a> +<a name="index-greater-than"></a> +</dd> +<dt><code>(gt:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p><code>STORE_FLAG_VALUE</code> if the <var>x</var> is greater than <var>y</var>. If they +are fixed-point, the comparison is done in a signed sense. +</p> +<a name="index-gtu"></a> +<a name="index-greater-than-1"></a> +<a name="index-unsigned-greater-than"></a> +</dd> +<dt><code>(gtu:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p>Like <code>gt</code> but does unsigned comparison, on fixed-point numbers only. +</p> +<a name="index-lt"></a> +<a name="index-less-than"></a> +<a name="index-ltu"></a> +<a name="index-unsigned-less-than"></a> +</dd> +<dt><code>(lt:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dt><code>(ltu:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p>Like <code>gt</code> and <code>gtu</code> but test for “less than”. +</p> +<a name="index-ge"></a> +<a name="index-greater-than-2"></a> +<a name="index-geu"></a> +<a name="index-unsigned-greater-than-1"></a> +</dd> +<dt><code>(ge:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dt><code>(geu:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p>Like <code>gt</code> and <code>gtu</code> but test for “greater than or equal”. +</p> +<a name="index-le"></a> +<a name="index-less-than-or-equal"></a> +<a name="index-leu"></a> +<a name="index-unsigned-less-than-1"></a> +</dd> +<dt><code>(le:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dt><code>(leu:<var>m</var> <var>x</var> <var>y</var>)</code></dt> +<dd><p>Like <code>gt</code> and <code>gtu</code> but test for “less than or equal”. +</p> +<a name="index-if_005fthen_005felse"></a> +</dd> +<dt><code>(if_then_else <var>cond</var> <var>then</var> <var>else</var>)</code></dt> +<dd><p>This is not a comparison operation but is listed here because it is +always used in conjunction with a comparison operation. To be +precise, <var>cond</var> is a comparison expression. This expression +represents a choice, according to <var>cond</var>, between the value +represented by <var>then</var> and the one represented by <var>else</var>. +</p> +<p>On most machines, <code>if_then_else</code> expressions are valid only +to express conditional jumps. +</p> +<a name="index-cond"></a> +</dd> +<dt><code>(cond [<var>test1</var> <var>value1</var> <var>test2</var> <var>value2</var> …] <var>default</var>)</code></dt> +<dd><p>Similar to <code>if_then_else</code>, but more general. Each of <var>test1</var>, +<var>test2</var>, … is performed in turn. The result of this expression is +the <var>value</var> corresponding to the first nonzero test, or <var>default</var> if +none of the tests are nonzero expressions. +</p> +<p>This is currently not valid for instruction patterns and is supported only +for insn attributes. See <a href="Insn-Attributes.html#Insn-Attributes">Insn Attributes</a>. +</p></dd> +</dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Bit_002dFields.html#Bit_002dFields" accesskey="n" rel="next">Bit-Fields</a>, Previous: <a href="Arithmetic.html#Arithmetic" accesskey="p" rel="previous">Arithmetic</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> |