huangmeng
/
Embedded_AI


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154
							<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2017 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 5.2, http://www.gnu.org/software/texinfo/ -->
<head>
<title>GNU Compiler Collection (GCC) Internals: Shrink-wrapping separate components</title>

<meta name="description" content="GNU Compiler Collection (GCC) Internals: Shrink-wrapping separate components">
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Shrink-wrapping separate components">
<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="Stack-and-Calling.html#Stack-and-Calling" rel="up" title="Stack and Calling">
<link href="Stack-Smashing-Protection.html#Stack-Smashing-Protection" rel="next" title="Stack Smashing Protection">
<link href="Tail-Calls.html#Tail-Calls" rel="prev" title="Tail Calls">
<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="Shrink_002dwrapping-separate-components"></a>
<div class="header">
<p>
Next: <a href="Stack-Smashing-Protection.html#Stack-Smashing-Protection" accesskey="n" rel="next">Stack Smashing Protection</a>, Previous: <a href="Tail-Calls.html#Tail-Calls" accesskey="p" rel="prev">Tail Calls</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</a> &nbsp; [<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="Shrink_002dwrapping-separate-components-1"></a>
<h4 class="subsection">17.9.14 Shrink-wrapping separate components</h4>
<a name="index-shrink_002dwrapping-separate-components"></a>

<p>The prologue may perform a variety of target dependent tasks such as
saving callee-saved registers, saving the return address, aligning the
stack, creating a stack frame, initializing the PIC register, setting
up the static chain, etc.
</p>
<p>On some targets some of these tasks may be independent of others and
thus may be shrink-wrapped separately.  These independent tasks are
referred to as components and are handled generically by the target
independent parts of GCC.
</p>
<p>Using the following hooks those prologue or epilogue components can be
shrink-wrapped separately, so that the initialization (and possibly
teardown) those components do is not done as frequently on execution
paths where this would unnecessary.
</p>
<p>What exactly those components are is up to the target code; the generic
code treats them abstractly, as a bit in an <code>sbitmap</code>.  These
<code>sbitmap</code>s are allocated by the <code>shrink_wrap.get_separate_components</code>
and <code>shrink_wrap.components_for_bb</code> hooks, and deallocated by the
generic code.
</p>
<dl>
<dt><a name="index-TARGET_005fSHRINK_005fWRAP_005fGET_005fSEPARATE_005fCOMPONENTS"></a>Target Hook: <em>sbitmap</em> <strong>TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS</strong> <em>(void)</em></dt>
<dd><p>This hook should return an <code>sbitmap</code> with the bits set for those
components that can be separately shrink-wrapped in the current function.
Return <code>NULL</code> if the current function should not get any separate
shrink-wrapping.
Don&rsquo;t define this hook if it would always return <code>NULL</code>.
If it is defined, the other hooks in this group have to be defined as well.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSHRINK_005fWRAP_005fCOMPONENTS_005fFOR_005fBB"></a>Target Hook: <em>sbitmap</em> <strong>TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB</strong> <em>(basic_block)</em></dt>
<dd><p>This hook should return an <code>sbitmap</code> with the bits set for those
components where either the prologue component has to be executed before
the <code>basic_block</code>, or the epilogue component after it, or both.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSHRINK_005fWRAP_005fDISQUALIFY_005fCOMPONENTS"></a>Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS</strong> <em>(sbitmap <var>components</var>, edge <var>e</var>, sbitmap <var>edge_components</var>, bool <var>is_prologue</var>)</em></dt>
<dd><p>This hook should clear the bits in the <var>components</var> bitmap for those
components in <var>edge_components</var> that the target cannot handle on edge
<var>e</var>, where <var>is_prologue</var> says if this is for a prologue or an
epilogue instead.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSHRINK_005fWRAP_005fEMIT_005fPROLOGUE_005fCOMPONENTS"></a>Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS</strong> <em>(sbitmap)</em></dt>
<dd><p>Emit prologue insns for the components indicated by the parameter.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSHRINK_005fWRAP_005fEMIT_005fEPILOGUE_005fCOMPONENTS"></a>Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS</strong> <em>(sbitmap)</em></dt>
<dd><p>Emit epilogue insns for the components indicated by the parameter.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSHRINK_005fWRAP_005fSET_005fHANDLED_005fCOMPONENTS"></a>Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS</strong> <em>(sbitmap)</em></dt>
<dd><p>Mark the components in the parameter as handled, so that the
<code>prologue</code> and <code>epilogue</code> named patterns know to ignore those
components.  The target code should not hang on to the <code>sbitmap</code>, it
will be deleted after this call.
</p></dd></dl>

<hr>
<div class="header">
<p>
Next: <a href="Stack-Smashing-Protection.html#Stack-Smashing-Protection" accesskey="n" rel="next">Stack Smashing Protection</a>, Previous: <a href="Tail-Calls.html#Tail-Calls" accesskey="p" rel="prev">Tail Calls</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</a> &nbsp; [<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>