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Copies published by the Free Software Foundation raise funds for GNU development. --> <!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ --> <head> <title>Shrink-wrapping separate components (GNU Compiler Collection (GCC) Internals)</title> <meta name="description" content="Shrink-wrapping separate components (GNU Compiler Collection (GCC) Internals)"> <meta name="keywords" content="Shrink-wrapping separate components (GNU Compiler Collection (GCC) Internals)"> <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.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} 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.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> </head> <body lang="en"> <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> [<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">18.9.14 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’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> [<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>