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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 |
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diff --git a/share/doc/gcc/Simple-Constraints.html b/share/doc/gcc/Simple-Constraints.html new file mode 100644 index 0000000..86a8a70 --- /dev/null +++ b/share/doc/gcc/Simple-Constraints.html @@ -0,0 +1,309 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +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>Using the GNU Compiler Collection (GCC): Simple Constraints</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Simple Constraints"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Simple Constraints"> +<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="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Constraints.html#Constraints" rel="up" title="Constraints"> +<link href="Multi_002dAlternative.html#Multi_002dAlternative" rel="next" title="Multi-Alternative"> +<link href="Constraints.html#Constraints" rel="previous" title="Constraints"> +<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_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Simple-Constraints"></a> +<div class="header"> +<p> +Next: <a href="Multi_002dAlternative.html#Multi_002dAlternative" accesskey="n" rel="next">Multi-Alternative</a>, Up: <a href="Constraints.html#Constraints" accesskey="u" rel="up">Constraints</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Simple-Constraints-1"></a> +<h4 class="subsubsection">6.47.3.1 Simple Constraints</h4> +<a name="index-simple-constraints"></a> + +<p>The simplest kind of constraint is a string full of letters, each of +which describes one kind of operand that is permitted. Here are +the letters that are allowed: +</p> +<dl compact="compact"> +<dt>whitespace</dt> +<dd><p>Whitespace characters are ignored and can be inserted at any position +except the first. This enables each alternative for different operands to +be visually aligned in the machine description even if they have different +number of constraints and modifiers. +</p> +<a name="index-m-in-constraint"></a> +<a name="index-memory-references-in-constraints"></a> +</dd> +<dt>‘<samp>m</samp>’</dt> +<dd><p>A memory operand is allowed, with any kind of address that the machine +supports in general. +Note that the letter used for the general memory constraint can be +re-defined by a back end using the <code>TARGET_MEM_CONSTRAINT</code> macro. +</p> +<a name="index-offsettable-address"></a> +<a name="index-o-in-constraint"></a> +</dd> +<dt>‘<samp>o</samp>’</dt> +<dd><p>A memory operand is allowed, but only if the address is +<em>offsettable</em>. This means that adding a small integer (actually, +the width in bytes of the operand, as determined by its machine mode) +may be added to the address and the result is also a valid memory +address. +</p> +<a name="index-autoincrement_002fdecrement-addressing"></a> +<p>For example, an address which is constant is offsettable; so is an +address that is the sum of a register and a constant (as long as a +slightly larger constant is also within the range of address-offsets +supported by the machine); but an autoincrement or autodecrement +address is not offsettable. More complicated indirect/indexed +addresses may or may not be offsettable depending on the other +addressing modes that the machine supports. +</p> +<p>Note that in an output operand which can be matched by another +operand, the constraint letter ‘<samp>o</samp>’ is valid only when accompanied +by both ‘<samp><</samp>’ (if the target machine has predecrement addressing) +and ‘<samp>></samp>’ (if the target machine has preincrement addressing). +</p> +<a name="index-V-in-constraint"></a> +</dd> +<dt>‘<samp>V</samp>’</dt> +<dd><p>A memory operand that is not offsettable. In other words, anything that +would fit the ‘<samp>m</samp>’ constraint but not the ‘<samp>o</samp>’ constraint. +</p> +<a name="index-_003c-in-constraint"></a> +</dd> +<dt>‘<samp><</samp>’</dt> +<dd><p>A memory operand with autodecrement addressing (either predecrement or +postdecrement) is allowed. In inline <code>asm</code> this constraint is only +allowed if the operand is used exactly once in an instruction that can +handle the side effects. Not using an operand with ‘<samp><</samp>’ in constraint +string in the inline <code>asm</code> pattern at all or using it in multiple +instructions isn’t valid, because the side effects wouldn’t be performed +or would be performed more than once. Furthermore, on some targets +the operand with ‘<samp><</samp>’ in constraint string must be accompanied by +special instruction suffixes like <code>%U0</code> instruction suffix on PowerPC +or <code>%P0</code> on IA-64. +</p> +<a name="index-_003e-in-constraint"></a> +</dd> +<dt>‘<samp>></samp>’</dt> +<dd><p>A memory operand with autoincrement addressing (either preincrement or +postincrement) is allowed. In inline <code>asm</code> the same restrictions +as for ‘<samp><</samp>’ apply. +</p> +<a name="index-r-in-constraint"></a> +<a name="index-registers-in-constraints"></a> +</dd> +<dt>‘<samp>r</samp>’</dt> +<dd><p>A register operand is allowed provided that it is in a general +register. +</p> +<a name="index-constants-in-constraints"></a> +<a name="index-i-in-constraint"></a> +</dd> +<dt>‘<samp>i</samp>’</dt> +<dd><p>An immediate integer operand (one with constant value) is allowed. +This includes symbolic constants whose values will be known only at +assembly time or later. +</p> +<a name="index-n-in-constraint"></a> +</dd> +<dt>‘<samp>n</samp>’</dt> +<dd><p>An immediate integer operand with a known numeric value is allowed. +Many systems cannot support assembly-time constants for operands less +than a word wide. Constraints for these operands should use ‘<samp>n</samp>’ +rather than ‘<samp>i</samp>’. +</p> +<a name="index-I-in-constraint"></a> +</dd> +<dt>‘<samp>I</samp>’, ‘<samp>J</samp>’, ‘<samp>K</samp>’, … ‘<samp>P</samp>’</dt> +<dd><p>Other letters in the range ‘<samp>I</samp>’ through ‘<samp>P</samp>’ may be defined in +a machine-dependent fashion to permit immediate integer operands with +explicit integer values in specified ranges. For example, on the +68000, ‘<samp>I</samp>’ is defined to stand for the range of values 1 to 8. +This is the range permitted as a shift count in the shift +instructions. +</p> +<a name="index-E-in-constraint"></a> +</dd> +<dt>‘<samp>E</samp>’</dt> +<dd><p>An immediate floating operand (expression code <code>const_double</code>) is +allowed, but only if the target floating point format is the same as +that of the host machine (on which the compiler is running). +</p> +<a name="index-F-in-constraint"></a> +</dd> +<dt>‘<samp>F</samp>’</dt> +<dd><p>An immediate floating operand (expression code <code>const_double</code> or +<code>const_vector</code>) is allowed. +</p> +<a name="index-G-in-constraint"></a> +<a name="index-H-in-constraint"></a> +</dd> +<dt>‘<samp>G</samp>’, ‘<samp>H</samp>’</dt> +<dd><p>‘<samp>G</samp>’ and ‘<samp>H</samp>’ may be defined in a machine-dependent fashion to +permit immediate floating operands in particular ranges of values. +</p> +<a name="index-s-in-constraint"></a> +</dd> +<dt>‘<samp>s</samp>’</dt> +<dd><p>An immediate integer operand whose value is not an explicit integer is +allowed. +</p> +<p>This might appear strange; if an insn allows a constant operand with a +value not known at compile time, it certainly must allow any known +value. So why use ‘<samp>s</samp>’ instead of ‘<samp>i</samp>’? Sometimes it allows +better code to be generated. +</p> +<p>For example, on the 68000 in a fullword instruction it is possible to +use an immediate operand; but if the immediate value is between -128 +and 127, better code results from loading the value into a register and +using the register. This is because the load into the register can be +done with a ‘<samp>moveq</samp>’ instruction. We arrange for this to happen +by defining the letter ‘<samp>K</samp>’ to mean “any integer outside the +range -128 to 127”, and then specifying ‘<samp>Ks</samp>’ in the operand +constraints. +</p> +<a name="index-g-in-constraint"></a> +</dd> +<dt>‘<samp>g</samp>’</dt> +<dd><p>Any register, memory or immediate integer operand is allowed, except for +registers that are not general registers. +</p> +<a name="index-X-in-constraint"></a> +</dd> +<dt>‘<samp>X</samp>’</dt> +<dd><p>Any operand whatsoever is allowed. +</p> +<a name="index-0-in-constraint"></a> +<a name="index-digits-in-constraint"></a> +</dd> +<dt>‘<samp>0</samp>’, ‘<samp>1</samp>’, ‘<samp>2</samp>’, … ‘<samp>9</samp>’</dt> +<dd><p>An operand that matches the specified operand number is allowed. If a +digit is used together with letters within the same alternative, the +digit should come last. +</p> +<p>This number is allowed to be more than a single digit. If multiple +digits are encountered consecutively, they are interpreted as a single +decimal integer. There is scant chance for ambiguity, since to-date +it has never been desirable that ‘<samp>10</samp>’ be interpreted as matching +either operand 1 <em>or</em> operand 0. Should this be desired, one +can use multiple alternatives instead. +</p> +<a name="index-matching-constraint"></a> +<a name="index-constraint_002c-matching"></a> +<p>This is called a <em>matching constraint</em> and what it really means is +that the assembler has only a single operand that fills two roles +which <code>asm</code> distinguishes. For example, an add instruction uses +two input operands and an output operand, but on most CISC +machines an add instruction really has only two operands, one of them an +input-output operand: +</p> +<div class="smallexample"> +<pre class="smallexample">addl #35,r12 +</pre></div> + +<p>Matching constraints are used in these circumstances. +More precisely, the two operands that match must include one input-only +operand and one output-only operand. Moreover, the digit must be a +smaller number than the number of the operand that uses it in the +constraint. +</p> + +<a name="index-load-address-instruction"></a> +<a name="index-push-address-instruction"></a> +<a name="index-address-constraints"></a> +<a name="index-p-in-constraint"></a> +</dd> +<dt>‘<samp>p</samp>’</dt> +<dd><p>An operand that is a valid memory address is allowed. This is +for “load address” and “push address” instructions. +</p> +<a name="index-address_005foperand"></a> +<p>‘<samp>p</samp>’ in the constraint must be accompanied by <code>address_operand</code> +as the predicate in the <code>match_operand</code>. This predicate interprets +the mode specified in the <code>match_operand</code> as the mode of the memory +reference for which the address would be valid. +</p> +<a name="index-other-register-constraints"></a> +<a name="index-extensible-constraints"></a> +</dd> +<dt><var>other-letters</var></dt> +<dd><p>Other letters can be defined in machine-dependent fashion to stand for +particular classes of registers or other arbitrary operand types. +‘<samp>d</samp>’, ‘<samp>a</samp>’ and ‘<samp>f</samp>’ are defined on the 68000/68020 to stand +for data, address and floating point registers. +</p></dd> +</dl> + + +<hr> +<div class="header"> +<p> +Next: <a href="Multi_002dAlternative.html#Multi_002dAlternative" accesskey="n" rel="next">Multi-Alternative</a>, Up: <a href="Constraints.html#Constraints" accesskey="u" rel="up">Constraints</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |