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diff --git a/share/doc/gccint/Leaf-Functions.html b/share/doc/gccint/Leaf-Functions.html new file mode 100644 index 0000000..09ac2f6 --- /dev/null +++ b/share/doc/gccint/Leaf-Functions.html @@ -0,0 +1,153 @@ +<!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: Leaf Functions</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Leaf Functions"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Leaf Functions"> +<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="Registers.html#Registers" rel="up" title="Registers"> +<link href="Stack-Registers.html#Stack-Registers" rel="next" title="Stack Registers"> +<link href="Values-in-Registers.html#Values-in-Registers" rel="previous" title="Values in 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="Leaf-Functions"></a> +<div class="header"> +<p> +Next: <a href="Stack-Registers.html#Stack-Registers" accesskey="n" rel="next">Stack Registers</a>, Previous: <a href="Values-in-Registers.html#Values-in-Registers" accesskey="p" rel="previous">Values in Registers</a>, Up: <a href="Registers.html#Registers" accesskey="u" rel="up">Registers</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="Handling-Leaf-Functions"></a> +<h4 class="subsection">18.7.4 Handling Leaf Functions</h4> + +<a name="index-leaf-functions"></a> +<a name="index-functions_002c-leaf"></a> +<p>On some machines, a leaf function (i.e., one which makes no calls) can run +more efficiently if it does not make its own register window. Often this +means it is required to receive its arguments in the registers where they +are passed by the caller, instead of the registers where they would +normally arrive. +</p> +<p>The special treatment for leaf functions generally applies only when +other conditions are met; for example, often they may use only those +registers for its own variables and temporaries. We use the term “leaf +function” to mean a function that is suitable for this special +handling, so that functions with no calls are not necessarily “leaf +functions”. +</p> +<p>GCC assigns register numbers before it knows whether the function is +suitable for leaf function treatment. So it needs to renumber the +registers in order to output a leaf function. The following macros +accomplish this. +</p> +<dl> +<dt><a name="index-LEAF_005fREGISTERS"></a>Macro: <strong>LEAF_REGISTERS</strong></dt> +<dd><p>Name of a char vector, indexed by hard register number, which +contains 1 for a register that is allowable in a candidate for leaf +function treatment. +</p> +<p>If leaf function treatment involves renumbering the registers, then the +registers marked here should be the ones before renumbering—those that +GCC would ordinarily allocate. The registers which will actually be +used in the assembler code, after renumbering, should not be marked with 1 +in this vector. +</p> +<p>Define this macro only if the target machine offers a way to optimize +the treatment of leaf functions. +</p></dd></dl> + +<dl> +<dt><a name="index-LEAF_005fREG_005fREMAP"></a>Macro: <strong>LEAF_REG_REMAP</strong> <em>(<var>regno</var>)</em></dt> +<dd><p>A C expression whose value is the register number to which <var>regno</var> +should be renumbered, when a function is treated as a leaf function. +</p> +<p>If <var>regno</var> is a register number which should not appear in a leaf +function before renumbering, then the expression should yield -1, which +will cause the compiler to abort. +</p> +<p>Define this macro only if the target machine offers a way to optimize the +treatment of leaf functions, and registers need to be renumbered to do +this. +</p></dd></dl> + +<a name="index-current_005ffunction_005fis_005fleaf"></a> +<a name="index-current_005ffunction_005fuses_005fonly_005fleaf_005fregs"></a> +<p><code>TARGET_ASM_FUNCTION_PROLOGUE</code> and +<code>TARGET_ASM_FUNCTION_EPILOGUE</code> must usually treat leaf functions +specially. They can test the C variable <code>current_function_is_leaf</code> +which is nonzero for leaf functions. <code>current_function_is_leaf</code> is +set prior to local register allocation and is valid for the remaining +compiler passes. They can also test the C variable +<code>current_function_uses_only_leaf_regs</code> which is nonzero for leaf +functions which only use leaf registers. +<code>current_function_uses_only_leaf_regs</code> is valid after all passes +that modify the instructions have been run and is only useful if +<code>LEAF_REGISTERS</code> is defined. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Stack-Registers.html#Stack-Registers" accesskey="n" rel="next">Stack Registers</a>, Previous: <a href="Values-in-Registers.html#Values-in-Registers" accesskey="p" rel="previous">Values in Registers</a>, Up: <a href="Registers.html#Registers" accesskey="u" rel="up">Registers</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> |