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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/Constant-expressions.html | |
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diff --git a/share/doc/gccint/Constant-expressions.html b/share/doc/gccint/Constant-expressions.html new file mode 100644 index 0000000..0f8c6c0 --- /dev/null +++ b/share/doc/gccint/Constant-expressions.html @@ -0,0 +1,261 @@ +<!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: Constant expressions</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Constant expressions"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Constant expressions"> +<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="Expression-trees.html#Expression-trees" rel="up" title="Expression trees"> +<link href="Storage-References.html#Storage-References" rel="next" title="Storage References"> +<link href="Expression-trees.html#Expression-trees" rel="previous" title="Expression trees"> +<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="Constant-expressions"></a> +<div class="header"> +<p> +Next: <a href="Storage-References.html#Storage-References" accesskey="n" rel="next">Storage References</a>, Up: <a href="Expression-trees.html#Expression-trees" accesskey="u" rel="up">Expression trees</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="Constant-expressions-1"></a> +<h4 class="subsection">11.6.1 Constant expressions</h4> +<a name="index-INTEGER_005fCST"></a> +<a name="index-tree_005fint_005fcst_005flt"></a> +<a name="index-tree_005fint_005fcst_005fequal"></a> +<a name="index-tree_005ffits_005fuhwi_005fp"></a> +<a name="index-tree_005ffits_005fshwi_005fp"></a> +<a name="index-tree_005fto_005fuhwi"></a> +<a name="index-tree_005fto_005fshwi"></a> +<a name="index-TREE_005fINT_005fCST_005fNUNITS"></a> +<a name="index-TREE_005fINT_005fCST_005fELT"></a> +<a name="index-TREE_005fINT_005fCST_005fLOW"></a> +<a name="index-REAL_005fCST"></a> +<a name="index-FIXED_005fCST"></a> +<a name="index-COMPLEX_005fCST"></a> +<a name="index-VECTOR_005fCST"></a> +<a name="index-STRING_005fCST"></a> +<a name="index-POLY_005fINT_005fCST"></a> +<a name="index-TREE_005fSTRING_005fLENGTH"></a> +<a name="index-TREE_005fSTRING_005fPOINTER"></a> + +<p>The table below begins with constants, moves on to unary expressions, +then proceeds to binary expressions, and concludes with various other +kinds of expressions: +</p> +<dl compact="compact"> +<dt><code>INTEGER_CST</code></dt> +<dd><p>These nodes represent integer constants. Note that the type of these +constants is obtained with <code>TREE_TYPE</code>; they are not always of type +<code>int</code>. In particular, <code>char</code> constants are represented with +<code>INTEGER_CST</code> nodes. The value of the integer constant <code>e</code> is +represented in an array of HOST_WIDE_INT. There are enough elements +in the array to represent the value without taking extra elements for +redundant 0s or -1. The number of elements used to represent <code>e</code> +is available via <code>TREE_INT_CST_NUNITS</code>. Element <code>i</code> can be +extracted by using <code>TREE_INT_CST_ELT (e, i)</code>. +<code>TREE_INT_CST_LOW</code> is a shorthand for <code>TREE_INT_CST_ELT (e, 0)</code>. +</p> +<p>The functions <code>tree_fits_shwi_p</code> and <code>tree_fits_uhwi_p</code> +can be used to tell if the value is small enough to fit in a +signed HOST_WIDE_INT or an unsigned HOST_WIDE_INT respectively. +The value can then be extracted using <code>tree_to_shwi</code> and +<code>tree_to_uhwi</code>. +</p> +</dd> +<dt><code>REAL_CST</code></dt> +<dd> +<p>FIXME: Talk about how to obtain representations of this constant, do +comparisons, and so forth. +</p> +</dd> +<dt><code>FIXED_CST</code></dt> +<dd> +<p>These nodes represent fixed-point constants. The type of these constants +is obtained with <code>TREE_TYPE</code>. <code>TREE_FIXED_CST_PTR</code> points to +a <code>struct fixed_value</code>; <code>TREE_FIXED_CST</code> returns the structure +itself. <code>struct fixed_value</code> contains <code>data</code> with the size of two +<code>HOST_BITS_PER_WIDE_INT</code> and <code>mode</code> as the associated fixed-point +machine mode for <code>data</code>. +</p> +</dd> +<dt><code>COMPLEX_CST</code></dt> +<dd><p>These nodes are used to represent complex number constants, that is a +<code>__complex__</code> whose parts are constant nodes. The +<code>TREE_REALPART</code> and <code>TREE_IMAGPART</code> return the real and the +imaginary parts respectively. +</p> +</dd> +<dt><code>VECTOR_CST</code></dt> +<dd><p>These nodes are used to represent vector constants. Each vector +constant <var>v</var> is treated as a specific instance of an arbitrary-length +sequence that itself contains ‘<samp>VECTOR_CST_NPATTERNS (<var>v</var>)</samp>’ +interleaved patterns. Each pattern has the form: +</p> +<div class="smallexample"> +<pre class="smallexample">{ <var>base0</var>, <var>base1</var>, <var>base1</var> + <var>step</var>, <var>base1</var> + <var>step</var> * 2, … } +</pre></div> + +<p>The first three elements in each pattern are enough to determine the +values of the other elements. However, if all <var>step</var>s are zero, +only the first two elements are needed. If in addition each <var>base1</var> +is equal to the corresponding <var>base0</var>, only the first element in +each pattern is needed. The number of encoded elements per pattern +is given by ‘<samp>VECTOR_CST_NELTS_PER_PATTERN (<var>v</var>)</samp>’. +</p> +<p>For example, the constant: +</p> +<div class="smallexample"> +<pre class="smallexample">{ 0, 1, 2, 6, 3, 8, 4, 10, 5, 12, 6, 14, 7, 16, 8, 18 } +</pre></div> + +<p>is interpreted as an interleaving of the sequences: +</p> +<div class="smallexample"> +<pre class="smallexample">{ 0, 2, 3, 4, 5, 6, 7, 8 } +{ 1, 6, 8, 10, 12, 14, 16, 18 } +</pre></div> + +<p>where the sequences are represented by the following patterns: +</p> +<div class="smallexample"> +<pre class="smallexample"><var>base0</var> == 0, <var>base1</var> == 2, <var>step</var> == 1 +<var>base0</var> == 1, <var>base1</var> == 6, <var>step</var> == 2 +</pre></div> + +<p>In this case: +</p> +<div class="smallexample"> +<pre class="smallexample">VECTOR_CST_NPATTERNS (<var>v</var>) == 2 +VECTOR_CST_NELTS_PER_PATTERN (<var>v</var>) == 3 +</pre></div> + +<p>The vector is therefore encoded using the first 6 elements +(‘<samp>{ 0, 1, 2, 6, 3, 8 }</samp>’), with the remaining 10 elements +being implicit extensions of them. +</p> +<p>Sometimes this scheme can create two possible encodings of the same +vector. For example { 0, 1 } could be seen as two patterns with +one element each or one pattern with two elements (<var>base0</var> and +<var>base1</var>). The canonical encoding is always the one with the +fewest patterns or (if both encodings have the same number of +petterns) the one with the fewest encoded elements. +</p> +<p>‘<samp>vector_cst_encoding_nelts (<var>v</var>)</samp>’ gives the total number of +encoded elements in <var>v</var>, which is 6 in the example above. +<code>VECTOR_CST_ENCODED_ELTS (<var>v</var>)</code> gives a pointer to the elements +encoded in <var>v</var> and <code>VECTOR_CST_ENCODED_ELT (<var>v</var>, <var>i</var>)</code> +accesses the value of encoded element <var>i</var>. +</p> +<p>‘<samp>VECTOR_CST_DUPLICATE_P (<var>v</var>)</samp>’ is true if <var>v</var> simply contains +repeated instances of ‘<samp>VECTOR_CST_NPATTERNS (<var>v</var>)</samp>’ values. This is +a shorthand for testing ‘<samp>VECTOR_CST_NELTS_PER_PATTERN (<var>v</var>) == 1</samp>’. +</p> +<p>‘<samp>VECTOR_CST_STEPPED_P (<var>v</var>)</samp>’ is true if at least one +pattern in <var>v</var> has a nonzero step. This is a shorthand for +testing ‘<samp>VECTOR_CST_NELTS_PER_PATTERN (<var>v</var>) == 3</samp>’. +</p> +<p>The utility function <code>vector_cst_elt</code> gives the value of an +arbitrary index as a <code>tree</code>. <code>vector_cst_int_elt</code> gives +the same value as a <code>wide_int</code>. +</p> +</dd> +<dt><code>STRING_CST</code></dt> +<dd><p>These nodes represent string-constants. The <code>TREE_STRING_LENGTH</code> +returns the length of the string, as an <code>int</code>. The +<code>TREE_STRING_POINTER</code> is a <code>char*</code> containing the string +itself. The string may not be <code>NUL</code>-terminated, and it may contain +embedded <code>NUL</code> characters. Therefore, the +<code>TREE_STRING_LENGTH</code> includes the trailing <code>NUL</code> if it is +present. +</p> +<p>For wide string constants, the <code>TREE_STRING_LENGTH</code> is the number +of bytes in the string, and the <code>TREE_STRING_POINTER</code> +points to an array of the bytes of the string, as represented on the +target system (that is, as integers in the target endianness). Wide and +non-wide string constants are distinguished only by the <code>TREE_TYPE</code> +of the <code>STRING_CST</code>. +</p> +<p>FIXME: The formats of string constants are not well-defined when the +target system bytes are not the same width as host system bytes. +</p> +</dd> +<dt><code>POLY_INT_CST</code></dt> +<dd><p>These nodes represent invariants that depend on some target-specific +runtime parameters. They consist of <code>NUM_POLY_INT_COEFFS</code> +coefficients, with the first coefficient being the constant term and +the others being multipliers that are applied to the runtime parameters. +</p> +<p><code>POLY_INT_CST_ELT (<var>x</var>, <var>i</var>)</code> references coefficient number +<var>i</var> of <code>POLY_INT_CST</code> node <var>x</var>. Each coefficient is an +<code>INTEGER_CST</code>. +</p> +</dd> +</dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Storage-References.html#Storage-References" accesskey="n" rel="next">Storage References</a>, Up: <a href="Expression-trees.html#Expression-trees" accesskey="u" rel="up">Expression trees</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> |