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158 lines
9.4 KiB
HTML
158 lines
9.4 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Mode Switching (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Mode Switching (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Mode Switching (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
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<link href="Target-Attributes.html#Target-Attributes" rel="next" title="Target Attributes">
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<link href="Floating-Point.html#Floating-Point" rel="prev" title="Floating Point">
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<style type="text/css">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Mode-Switching"></a>
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<div class="header">
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<p>
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Next: <a href="Target-Attributes.html#Target-Attributes" accesskey="n" rel="next">Target Attributes</a>, Previous: <a href="Floating-Point.html#Floating-Point" accesskey="p" rel="prev">Floating Point</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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>
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</div>
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<hr>
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<a name="Mode-Switching-Instructions"></a>
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<h3 class="section">18.23 Mode Switching Instructions</h3>
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<a name="index-mode-switching"></a>
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<p>The following macros control mode switching optimizations:
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</p>
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<dl>
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<dt><a name="index-OPTIMIZE_005fMODE_005fSWITCHING"></a>Macro: <strong>OPTIMIZE_MODE_SWITCHING</strong> <em>(<var>entity</var>)</em></dt>
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<dd><p>Define this macro if the port needs extra instructions inserted for mode
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switching in an optimizing compilation.
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</p>
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<p>For an example, the SH4 can perform both single and double precision
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floating point operations, but to perform a single precision operation,
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the FPSCR PR bit has to be cleared, while for a double precision
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operation, this bit has to be set. Changing the PR bit requires a general
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purpose register as a scratch register, hence these FPSCR sets have to
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be inserted before reload, i.e. you cannot put this into instruction emitting
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or <code>TARGET_MACHINE_DEPENDENT_REORG</code>.
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</p>
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<p>You can have multiple entities that are mode-switched, and select at run time
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which entities actually need it. <code>OPTIMIZE_MODE_SWITCHING</code> should
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return nonzero for any <var>entity</var> that needs mode-switching.
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If you define this macro, you also have to define
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<code>NUM_MODES_FOR_MODE_SWITCHING</code>, <code>TARGET_MODE_NEEDED</code>,
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<code>TARGET_MODE_PRIORITY</code> and <code>TARGET_MODE_EMIT</code>.
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<code>TARGET_MODE_AFTER</code>, <code>TARGET_MODE_ENTRY</code>, and <code>TARGET_MODE_EXIT</code>
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are optional.
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</p></dd></dl>
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<dl>
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<dt><a name="index-NUM_005fMODES_005fFOR_005fMODE_005fSWITCHING"></a>Macro: <strong>NUM_MODES_FOR_MODE_SWITCHING</strong></dt>
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<dd><p>If you define <code>OPTIMIZE_MODE_SWITCHING</code>, you have to define this as
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initializer for an array of integers. Each initializer element
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N refers to an entity that needs mode switching, and specifies the number
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of different modes that might need to be set for this entity.
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The position of the initializer in the initializer—starting counting at
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zero—determines the integer that is used to refer to the mode-switched
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entity in question.
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In macros that take mode arguments / yield a mode result, modes are
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represented as numbers 0 … N - 1. N is used to specify that no mode
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switch is needed / supplied.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMODE_005fEMIT"></a>Target Hook: <em>void</em> <strong>TARGET_MODE_EMIT</strong> <em>(int <var>entity</var>, int <var>mode</var>, int <var>prev_mode</var>, HARD_REG_SET <var>regs_live</var>)</em></dt>
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<dd><p>Generate one or more insns to set <var>entity</var> to <var>mode</var>. <var>hard_reg_live</var> is the set of hard registers live at the point where the insn(s) are to be inserted. <var>prev_moxde</var> indicates the mode to switch from. Sets of a lower numbered entity will be emitted before sets of a higher numbered entity to a mode of the same or lower priority.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMODE_005fNEEDED"></a>Target Hook: <em>int</em> <strong>TARGET_MODE_NEEDED</strong> <em>(int <var>entity</var>, rtx_insn *<var>insn</var>)</em></dt>
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<dd><p><var>entity</var> is an integer specifying a mode-switched entity. If <code>OPTIMIZE_MODE_SWITCHING</code> is defined, you must define this macro to return an integer value not larger than the corresponding element in <code>NUM_MODES_FOR_MODE_SWITCHING</code>, to denote the mode that <var>entity</var> must be switched into prior to the execution of <var>insn</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMODE_005fAFTER"></a>Target Hook: <em>int</em> <strong>TARGET_MODE_AFTER</strong> <em>(int <var>entity</var>, int <var>mode</var>, rtx_insn *<var>insn</var>)</em></dt>
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<dd><p><var>entity</var> is an integer specifying a mode-switched entity. If this macro is defined, it is evaluated for every <var>insn</var> during mode switching. It determines the mode that an insn results in (if different from the incoming mode).
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMODE_005fENTRY"></a>Target Hook: <em>int</em> <strong>TARGET_MODE_ENTRY</strong> <em>(int <var>entity</var>)</em></dt>
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<dd><p>If this macro is defined, it is evaluated for every <var>entity</var> that needs mode switching. It should evaluate to an integer, which is a mode that <var>entity</var> is assumed to be switched to at function entry. If <code>TARGET_MODE_ENTRY</code> is defined then <code>TARGET_MODE_EXIT</code> must be defined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMODE_005fEXIT"></a>Target Hook: <em>int</em> <strong>TARGET_MODE_EXIT</strong> <em>(int <var>entity</var>)</em></dt>
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<dd><p>If this macro is defined, it is evaluated for every <var>entity</var> that needs mode switching. It should evaluate to an integer, which is a mode that <var>entity</var> is assumed to be switched to at function exit. If <code>TARGET_MODE_EXIT</code> is defined then <code>TARGET_MODE_ENTRY</code> must be defined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fMODE_005fPRIORITY"></a>Target Hook: <em>int</em> <strong>TARGET_MODE_PRIORITY</strong> <em>(int <var>entity</var>, int <var>n</var>)</em></dt>
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<dd><p>This macro specifies the order in which modes for <var>entity</var> are processed. 0 is the highest priority, <code>NUM_MODES_FOR_MODE_SWITCHING[<var>entity</var>] - 1</code> the lowest. The value of the macro should be an integer designating a mode for <var>entity</var>. For any fixed <var>entity</var>, <code>mode_priority</code> (<var>entity</var>, <var>n</var>) shall be a bijection in 0 … <code>num_modes_for_mode_switching[<var>entity</var>] - 1</code>.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Target-Attributes.html#Target-Attributes" accesskey="n" rel="next">Target Attributes</a>, Previous: <a href="Floating-Point.html#Floating-Point" accesskey="p" rel="prev">Floating Point</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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>
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</div>
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</body>
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</html>
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