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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 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/Elimination.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gccint/Elimination.html b/share/doc/gccint/Elimination.html new file mode 100644 index 0000000..69fd77b --- /dev/null +++ b/share/doc/gccint/Elimination.html @@ -0,0 +1,172 @@ +<!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: Elimination</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Elimination"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Elimination"> +<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-Arguments.html#Stack-Arguments" rel="next" title="Stack Arguments"> +<link href="Frame-Registers.html#Frame-Registers" rel="previous" title="Frame Registers"> +<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="Elimination"></a> +<div class="header"> +<p> +Next: <a href="Stack-Arguments.html#Stack-Arguments" accesskey="n" rel="next">Stack Arguments</a>, Previous: <a href="Frame-Registers.html#Frame-Registers" accesskey="p" rel="previous">Frame Registers</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="Eliminating-Frame-Pointer-and-Arg-Pointer"></a> +<h4 class="subsection">18.9.5 Eliminating Frame Pointer and Arg Pointer</h4> + +<p>This is about eliminating the frame pointer and arg pointer. +</p> +<dl> +<dt><a name="index-TARGET_005fFRAME_005fPOINTER_005fREQUIRED"></a>Target Hook: <em>bool</em> <strong>TARGET_FRAME_POINTER_REQUIRED</strong> <em>(void)</em></dt> +<dd><p>This target hook should return <code>true</code> if a function must have and use +a frame pointer. This target hook is called in the reload pass. If its return +value is <code>true</code> the function will have a frame pointer. +</p> +<p>This target hook can in principle examine the current function and decide +according to the facts, but on most machines the constant <code>false</code> or the +constant <code>true</code> suffices. Use <code>false</code> when the machine allows code +to be generated with no frame pointer, and doing so saves some time or space. +Use <code>true</code> when there is no possible advantage to avoiding a frame +pointer. +</p> +<p>In certain cases, the compiler does not know how to produce valid code +without a frame pointer. The compiler recognizes those cases and +automatically gives the function a frame pointer regardless of what +<code>targetm.frame_pointer_required</code> returns. You don’t need to worry about +them. +</p> +<p>In a function that does not require a frame pointer, the frame pointer +register can be allocated for ordinary usage, unless you mark it as a +fixed register. See <code>FIXED_REGISTERS</code> for more information. +</p> +<p>Default return value is <code>false</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-ELIMINABLE_005fREGS"></a>Macro: <strong>ELIMINABLE_REGS</strong></dt> +<dd><p>This macro specifies a table of register pairs used to eliminate +unneeded registers that point into the stack frame. +</p> +<p>The definition of this macro is a list of structure initializations, each +of which specifies an original and replacement register. +</p> +<p>On some machines, the position of the argument pointer is not known until +the compilation is completed. In such a case, a separate hard register +must be used for the argument pointer. This register can be eliminated by +replacing it with either the frame pointer or the argument pointer, +depending on whether or not the frame pointer has been eliminated. +</p> +<p>In this case, you might specify: +</p><div class="smallexample"> +<pre class="smallexample">#define ELIMINABLE_REGS \ +{{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM}, \ + {ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM}, \ + {FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM}} +</pre></div> + +<p>Note that the elimination of the argument pointer with the stack pointer is +specified first since that is the preferred elimination. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fCAN_005fELIMINATE"></a>Target Hook: <em>bool</em> <strong>TARGET_CAN_ELIMINATE</strong> <em>(const int <var>from_reg</var>, const int <var>to_reg</var>)</em></dt> +<dd><p>This target hook should return <code>true</code> if the compiler is allowed to +try to replace register number <var>from_reg</var> with register number +<var>to_reg</var>. This target hook will usually be <code>true</code>, since most of the +cases preventing register elimination are things that the compiler already +knows about. +</p> +<p>Default return value is <code>true</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-INITIAL_005fELIMINATION_005fOFFSET"></a>Macro: <strong>INITIAL_ELIMINATION_OFFSET</strong> <em>(<var>from-reg</var>, <var>to-reg</var>, <var>offset-var</var>)</em></dt> +<dd><p>This macro returns the initial difference between the specified pair +of registers. The value would be computed from information +such as the result of <code>get_frame_size ()</code> and the tables of +registers <code>df_regs_ever_live_p</code> and <code>call_used_regs</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fCOMPUTE_005fFRAME_005fLAYOUT"></a>Target Hook: <em>void</em> <strong>TARGET_COMPUTE_FRAME_LAYOUT</strong> <em>(void)</em></dt> +<dd><p>This target hook is called once each time the frame layout needs to be +recalculated. The calculations can be cached by the target and can then +be used by <code>INITIAL_ELIMINATION_OFFSET</code> instead of re-computing the +layout on every invocation of that hook. This is particularly useful +for targets that have an expensive frame layout function. Implementing +this callback is optional. +</p></dd></dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Stack-Arguments.html#Stack-Arguments" accesskey="n" rel="next">Stack Arguments</a>, Previous: <a href="Frame-Registers.html#Frame-Registers" accesskey="p" rel="previous">Frame Registers</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> |