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diff --git a/share/doc/gccint/Tuple-representation.html b/share/doc/gccint/Tuple-representation.html new file mode 100644 index 0000000..67f5e26 --- /dev/null +++ b/share/doc/gccint/Tuple-representation.html @@ -0,0 +1,297 @@ +<!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: Tuple representation</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Tuple representation"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Tuple representation"> +<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="GIMPLE.html#GIMPLE" rel="up" title="GIMPLE"> +<link href="Class-hierarchy-of-GIMPLE-statements.html#Class-hierarchy-of-GIMPLE-statements" rel="next" title="Class hierarchy of GIMPLE statements"> +<link href="GIMPLE.html#GIMPLE" rel="previous" title="GIMPLE"> +<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="Tuple-representation"></a> +<div class="header"> +<p> +Next: <a href="Class-hierarchy-of-GIMPLE-statements.html#Class-hierarchy-of-GIMPLE-statements" accesskey="n" rel="next">Class hierarchy of GIMPLE statements</a>, Up: <a href="GIMPLE.html#GIMPLE" accesskey="u" rel="up">GIMPLE</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="Tuple-representation-1"></a> +<h3 class="section">12.1 Tuple representation</h3> +<a name="index-tuples"></a> + +<p>GIMPLE instructions are tuples of variable size divided in two +groups: a header describing the instruction and its locations, +and a variable length body with all the operands. Tuples are +organized into a hierarchy with 3 main classes of tuples. +</p> +<a name="gimple-_0028gsbase_0029"></a> +<h4 class="subsection">12.1.1 <code>gimple</code> (gsbase)</h4> +<a name="index-gimple"></a> + +<p>This is the root of the hierarchy, it holds basic information +needed by most GIMPLE statements. There are some fields that +may not be relevant to every GIMPLE statement, but those were +moved into the base structure to take advantage of holes left by +other fields (thus making the structure more compact). The +structure takes 4 words (32 bytes) on 64 bit hosts: +</p> +<table> +<tr><td>Field</td><td>Size (bits)</td></tr> +<tr><td><code>code</code></td><td>8</td></tr> +<tr><td><code>subcode</code></td><td>16</td></tr> +<tr><td><code>no_warning</code></td><td>1</td></tr> +<tr><td><code>visited</code></td><td>1</td></tr> +<tr><td><code>nontemporal_move</code></td><td>1</td></tr> +<tr><td><code>plf</code></td><td>2</td></tr> +<tr><td><code>modified</code></td><td>1</td></tr> +<tr><td><code>has_volatile_ops</code></td><td>1</td></tr> +<tr><td><code>references_memory_p</code></td><td>1</td></tr> +<tr><td><code>uid</code></td><td>32</td></tr> +<tr><td><code>location</code></td><td>32</td></tr> +<tr><td><code>num_ops</code></td><td>32</td></tr> +<tr><td><code>bb</code></td><td>64</td></tr> +<tr><td><code>block</code></td><td>63</td></tr> +<tr><td>Total size</td><td>32 bytes</td></tr> +</table> + +<ul> +<li> <code>code</code> +Main identifier for a GIMPLE instruction. + +</li><li> <code>subcode</code> +Used to distinguish different variants of the same basic +instruction or provide flags applicable to a given code. The +<code>subcode</code> flags field has different uses depending on the code of +the instruction, but mostly it distinguishes instructions of the +same family. The most prominent use of this field is in +assignments, where subcode indicates the operation done on the +RHS of the assignment. For example, a = b + c is encoded as +<code>GIMPLE_ASSIGN <PLUS_EXPR, a, b, c></code>. + +</li><li> <code>no_warning</code> +Bitflag to indicate whether a warning has already been issued on +this statement. + +</li><li> <code>visited</code> +General purpose “visited” marker. Set and cleared by each pass +when needed. + +</li><li> <code>nontemporal_move</code> +Bitflag used in assignments that represent non-temporal moves. +Although this bitflag is only used in assignments, it was moved +into the base to take advantage of the bit holes left by the +previous fields. + +</li><li> <code>plf</code> +Pass Local Flags. This 2-bit mask can be used as general purpose +markers by any pass. Passes are responsible for clearing and +setting these two flags accordingly. + +</li><li> <code>modified</code> +Bitflag to indicate whether the statement has been modified. +Used mainly by the operand scanner to determine when to re-scan a +statement for operands. + +</li><li> <code>has_volatile_ops</code> +Bitflag to indicate whether this statement contains operands that +have been marked volatile. + +</li><li> <code>references_memory_p</code> +Bitflag to indicate whether this statement contains memory +references (i.e., its operands are either global variables, or +pointer dereferences or anything that must reside in memory). + +</li><li> <code>uid</code> +This is an unsigned integer used by passes that want to assign +IDs to every statement. These IDs must be assigned and used by +each pass. + +</li><li> <code>location</code> +This is a <code>location_t</code> identifier to specify source code +location for this statement. It is inherited from the front +end. + +</li><li> <code>num_ops</code> +Number of operands that this statement has. This specifies the +size of the operand vector embedded in the tuple. Only used in +some tuples, but it is declared in the base tuple to take +advantage of the 32-bit hole left by the previous fields. + +</li><li> <code>bb</code> +Basic block holding the instruction. + +</li><li> <code>block</code> +Lexical block holding this statement. Also used for debug +information generation. +</li></ul> + +<a name="gimple_005fstatement_005fwith_005fops"></a> +<h4 class="subsection">12.1.2 <code>gimple_statement_with_ops</code></h4> +<a name="index-gimple_005fstatement_005fwith_005fops"></a> + +<p>This tuple is actually split in two: +<code>gimple_statement_with_ops_base</code> and +<code>gimple_statement_with_ops</code>. This is needed to accommodate the +way the operand vector is allocated. The operand vector is +defined to be an array of 1 element. So, to allocate a dynamic +number of operands, the memory allocator (<code>gimple_alloc</code>) simply +allocates enough memory to hold the structure itself plus <code>N +- 1</code> operands which run “off the end” of the structure. For +example, to allocate space for a tuple with 3 operands, +<code>gimple_alloc</code> reserves <code>sizeof (struct +gimple_statement_with_ops) + 2 * sizeof (tree)</code> bytes. +</p> +<p>On the other hand, several fields in this tuple need to be shared +with the <code>gimple_statement_with_memory_ops</code> tuple. So, these +common fields are placed in <code>gimple_statement_with_ops_base</code> which +is then inherited from the other two tuples. +</p> + +<table> +<tr><td><code>gsbase</code></td><td>256</td></tr> +<tr><td><code>def_ops</code></td><td>64</td></tr> +<tr><td><code>use_ops</code></td><td>64</td></tr> +<tr><td><code>op</code></td><td><code>num_ops</code> * 64</td></tr> +<tr><td>Total size</td><td>48 + 8 * <code>num_ops</code> bytes</td></tr> +</table> + +<ul> +<li> <code>gsbase</code> +Inherited from <code>struct gimple</code>. + +</li><li> <code>def_ops</code> +Array of pointers into the operand array indicating all the slots that +contain a variable written-to by the statement. This array is +also used for immediate use chaining. Note that it would be +possible to not rely on this array, but the changes required to +implement this are pretty invasive. + +</li><li> <code>use_ops</code> +Similar to <code>def_ops</code> but for variables read by the statement. + +</li><li> <code>op</code> +Array of trees with <code>num_ops</code> slots. +</li></ul> + +<a name="gimple_005fstatement_005fwith_005fmemory_005fops"></a> +<h4 class="subsection">12.1.3 <code>gimple_statement_with_memory_ops</code></h4> + +<p>This tuple is essentially identical to <code>gimple_statement_with_ops</code>, +except that it contains 4 additional fields to hold vectors +related memory stores and loads. Similar to the previous case, +the structure is split in two to accommodate for the operand +vector (<code>gimple_statement_with_memory_ops_base</code> and +<code>gimple_statement_with_memory_ops</code>). +</p> + +<table> +<tr><td>Field</td><td>Size (bits)</td></tr> +<tr><td><code>gsbase</code></td><td>256</td></tr> +<tr><td><code>def_ops</code></td><td>64</td></tr> +<tr><td><code>use_ops</code></td><td>64</td></tr> +<tr><td><code>vdef_ops</code></td><td>64</td></tr> +<tr><td><code>vuse_ops</code></td><td>64</td></tr> +<tr><td><code>stores</code></td><td>64</td></tr> +<tr><td><code>loads</code></td><td>64</td></tr> +<tr><td><code>op</code></td><td><code>num_ops</code> * 64</td></tr> +<tr><td>Total size</td><td>80 + 8 * <code>num_ops</code> bytes</td></tr> +</table> + +<ul> +<li> <code>vdef_ops</code> +Similar to <code>def_ops</code> but for <code>VDEF</code> operators. There is +one entry per memory symbol written by this statement. This is +used to maintain the memory SSA use-def and def-def chains. + +</li><li> <code>vuse_ops</code> +Similar to <code>use_ops</code> but for <code>VUSE</code> operators. There is +one entry per memory symbol loaded by this statement. This is +used to maintain the memory SSA use-def chains. + +</li><li> <code>stores</code> +Bitset with all the UIDs for the symbols written-to by the +statement. This is different than <code>vdef_ops</code> in that all the +affected symbols are mentioned in this set. If memory +partitioning is enabled, the <code>vdef_ops</code> vector will refer to memory +partitions. Furthermore, no SSA information is stored in this +set. + +</li><li> <code>loads</code> +Similar to <code>stores</code>, but for memory loads. (Note that there +is some amount of redundancy here, it should be possible to +reduce memory utilization further by removing these sets). +</li></ul> + +<p>All the other tuples are defined in terms of these three basic +ones. Each tuple will add some fields. +</p> + +<hr> +<div class="header"> +<p> +Next: <a href="Class-hierarchy-of-GIMPLE-statements.html#Class-hierarchy-of-GIMPLE-statements" accesskey="n" rel="next">Class hierarchy of GIMPLE statements</a>, Up: <a href="GIMPLE.html#GIMPLE" accesskey="u" rel="up">GIMPLE</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> |