| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 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: Caller Saves</title> |
| |
| <meta name="description" content="GNU Compiler Collection (GCC) Internals: Caller Saves"> |
| <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Caller Saves"> |
| <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="Function-Entry.html#Function-Entry" rel="next" title="Function Entry"> |
| <link href="Aggregate-Return.html#Aggregate-Return" rel="prev" title="Aggregate Return"> |
| <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="Caller-Saves"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Function-Entry.html#Function-Entry" accesskey="n" rel="next">Function Entry</a>, Previous: <a href="Aggregate-Return.html#Aggregate-Return" accesskey="p" rel="prev">Aggregate Return</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="Caller_002dSaves-Register-Allocation"></a> |
| <h4 class="subsection">17.10.10 Caller-Saves Register Allocation</h4> |
| |
| <p>If you enable it, GCC can save registers around function calls. This |
| makes it possible to use call-clobbered registers to hold variables that |
| must live across calls. |
| </p> |
| <dl> |
| <dt><a name="index-CALLER_005fSAVE_005fPROFITABLE"></a>Macro: <strong>CALLER_SAVE_PROFITABLE</strong> <em>(<var>refs</var>, <var>calls</var>)</em></dt> |
| <dd><p>A C expression to determine whether it is worthwhile to consider placing |
| a pseudo-register in a call-clobbered hard register and saving and |
| restoring it around each function call. The expression should be 1 when |
| this is worth doing, and 0 otherwise. |
| </p> |
| <p>If you don’t define this macro, a default is used which is good on most |
| machines: <code>4 * <var>calls</var> < <var>refs</var></code>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-HARD_005fREGNO_005fCALLER_005fSAVE_005fMODE"></a>Macro: <strong>HARD_REGNO_CALLER_SAVE_MODE</strong> <em>(<var>regno</var>, <var>nregs</var>)</em></dt> |
| <dd><p>A C expression specifying which mode is required for saving <var>nregs</var> |
| of a pseudo-register in call-clobbered hard register <var>regno</var>. If |
| <var>regno</var> is unsuitable for caller save, <code>VOIDmode</code> should be |
| returned. For most machines this macro need not be defined since GCC |
| will select the smallest suitable mode. |
| </p></dd></dl> |
| |
| |
| |
| |
| </body> |
| </html> |
