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364 lines
23 KiB
HTML
4 years ago
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<title>Machine Modes - GNU Compiler Collection (GCC) Internals</title>
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<link rel="prev" href="Flags.html#Flags" title="Flags">
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<link rel="next" href="Constants.html#Constants" title="Constants">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<body>
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<div class="node">
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<a name="Machine-Modes"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Constants.html#Constants">Constants</a>,
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Previous: <a rel="previous" accesskey="p" href="Flags.html#Flags">Flags</a>,
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Up: <a rel="up" accesskey="u" href="RTL.html#RTL">RTL</a>
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<hr>
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</div>
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<h3 class="section">13.6 Machine Modes</h3>
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<p><a name="index-machine-modes-2728"></a>
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<a name="index-machine_005fmode-2729"></a>A machine mode describes a size of data object and the representation used
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for it. In the C code, machine modes are represented by an enumeration
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type, <code>machine_mode</code>, defined in <samp><span class="file">machmode.def</span></samp>. Each RTL
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expression has room for a machine mode and so do certain kinds of tree
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expressions (declarations and types, to be precise).
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<p>In debugging dumps and machine descriptions, the machine mode of an RTL
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expression is written after the expression code with a colon to separate
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them. The letters ‘<samp><span class="samp">mode</span></samp>’ which appear at the end of each machine mode
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name are omitted. For example, <code>(reg:SI 38)</code> is a <code>reg</code>
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expression with machine mode <code>SImode</code>. If the mode is
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<code>VOIDmode</code>, it is not written at all.
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<p>Here is a table of machine modes. The term “byte” below refers to an
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object of <code>BITS_PER_UNIT</code> bits (see <a href="Storage-Layout.html#Storage-Layout">Storage Layout</a>).
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<a name="index-BImode-2730"></a>
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<dl><dt><code>BImode</code><dd>“Bit” mode represents a single bit, for predicate registers.
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<p><a name="index-QImode-2731"></a><br><dt><code>QImode</code><dd>“Quarter-Integer” mode represents a single byte treated as an integer.
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<p><a name="index-HImode-2732"></a><br><dt><code>HImode</code><dd>“Half-Integer” mode represents a two-byte integer.
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<p><a name="index-PSImode-2733"></a><br><dt><code>PSImode</code><dd>“Partial Single Integer” mode represents an integer which occupies
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four bytes but which doesn't really use all four. On some machines,
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this is the right mode to use for pointers.
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<p><a name="index-SImode-2734"></a><br><dt><code>SImode</code><dd>“Single Integer” mode represents a four-byte integer.
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<p><a name="index-PDImode-2735"></a><br><dt><code>PDImode</code><dd>“Partial Double Integer” mode represents an integer which occupies
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eight bytes but which doesn't really use all eight. On some machines,
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this is the right mode to use for certain pointers.
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<p><a name="index-DImode-2736"></a><br><dt><code>DImode</code><dd>“Double Integer” mode represents an eight-byte integer.
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<p><a name="index-TImode-2737"></a><br><dt><code>TImode</code><dd>“Tetra Integer” (?) mode represents a sixteen-byte integer.
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<p><a name="index-OImode-2738"></a><br><dt><code>OImode</code><dd>“Octa Integer” (?) mode represents a thirty-two-byte integer.
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<p><a name="index-XImode-2739"></a><br><dt><code>XImode</code><dd>“Hexadeca Integer” (?) mode represents a sixty-four-byte integer.
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<p><a name="index-QFmode-2740"></a><br><dt><code>QFmode</code><dd>“Quarter-Floating” mode represents a quarter-precision (single byte)
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floating point number.
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<p><a name="index-HFmode-2741"></a><br><dt><code>HFmode</code><dd>“Half-Floating” mode represents a half-precision (two byte) floating
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point number.
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<p><a name="index-TQFmode-2742"></a><br><dt><code>TQFmode</code><dd>“Three-Quarter-Floating” (?) mode represents a three-quarter-precision
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(three byte) floating point number.
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<p><a name="index-SFmode-2743"></a><br><dt><code>SFmode</code><dd>“Single Floating” mode represents a four byte floating point number.
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In the common case, of a processor with IEEE arithmetic and 8-bit bytes,
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this is a single-precision IEEE floating point number; it can also be
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used for double-precision (on processors with 16-bit bytes) and
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single-precision VAX and IBM types.
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<p><a name="index-DFmode-2744"></a><br><dt><code>DFmode</code><dd>“Double Floating” mode represents an eight byte floating point number.
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In the common case, of a processor with IEEE arithmetic and 8-bit bytes,
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this is a double-precision IEEE floating point number.
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<p><a name="index-XFmode-2745"></a><br><dt><code>XFmode</code><dd>“Extended Floating” mode represents an IEEE extended floating point
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number. This mode only has 80 meaningful bits (ten bytes). Some
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processors require such numbers to be padded to twelve bytes, others
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to sixteen; this mode is used for either.
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<p><a name="index-SDmode-2746"></a><br><dt><code>SDmode</code><dd>“Single Decimal Floating” mode represents a four byte decimal
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floating point number (as distinct from conventional binary floating
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point).
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<p><a name="index-DDmode-2747"></a><br><dt><code>DDmode</code><dd>“Double Decimal Floating” mode represents an eight byte decimal
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floating point number.
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<p><a name="index-TDmode-2748"></a><br><dt><code>TDmode</code><dd>“Tetra Decimal Floating” mode represents a sixteen byte decimal
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floating point number all 128 of whose bits are meaningful.
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<p><a name="index-TFmode-2749"></a><br><dt><code>TFmode</code><dd>“Tetra Floating” mode represents a sixteen byte floating point number
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all 128 of whose bits are meaningful. One common use is the
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IEEE quad-precision format.
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<p><a name="index-QQmode-2750"></a><br><dt><code>QQmode</code><dd>“Quarter-Fractional” mode represents a single byte treated as a signed
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fractional number. The default format is “s.7”.
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<p><a name="index-HQmode-2751"></a><br><dt><code>HQmode</code><dd>“Half-Fractional” mode represents a two-byte signed fractional number.
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The default format is “s.15”.
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<p><a name="index-SQmode-2752"></a><br><dt><code>SQmode</code><dd>“Single Fractional” mode represents a four-byte signed fractional number.
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The default format is “s.31”.
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<p><a name="index-DQmode-2753"></a><br><dt><code>DQmode</code><dd>“Double Fractional” mode represents an eight-byte signed fractional number.
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The default format is “s.63”.
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<p><a name="index-TQmode-2754"></a><br><dt><code>TQmode</code><dd>“Tetra Fractional” mode represents a sixteen-byte signed fractional number.
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The default format is “s.127”.
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<p><a name="index-UQQmode-2755"></a><br><dt><code>UQQmode</code><dd>“Unsigned Quarter-Fractional” mode represents a single byte treated as an
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unsigned fractional number. The default format is “.8”.
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<p><a name="index-UHQmode-2756"></a><br><dt><code>UHQmode</code><dd>“Unsigned Half-Fractional” mode represents a two-byte unsigned fractional
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number. The default format is “.16”.
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<p><a name="index-USQmode-2757"></a><br><dt><code>USQmode</code><dd>“Unsigned Single Fractional” mode represents a four-byte unsigned fractional
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number. The default format is “.32”.
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<p><a name="index-UDQmode-2758"></a><br><dt><code>UDQmode</code><dd>“Unsigned Double Fractional” mode represents an eight-byte unsigned
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fractional number. The default format is “.64”.
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<p><a name="index-UTQmode-2759"></a><br><dt><code>UTQmode</code><dd>“Unsigned Tetra Fractional” mode represents a sixteen-byte unsigned
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fractional number. The default format is “.128”.
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<p><a name="index-HAmode-2760"></a><br><dt><code>HAmode</code><dd>“Half-Accumulator” mode represents a two-byte signed accumulator.
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The default format is “s8.7”.
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<p><a name="index-SAmode-2761"></a><br><dt><code>SAmode</code><dd>“Single Accumulator” mode represents a four-byte signed accumulator.
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The default format is “s16.15”.
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<p><a name="index-DAmode-2762"></a><br><dt><code>DAmode</code><dd>“Double Accumulator” mode represents an eight-byte signed accumulator.
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The default format is “s32.31”.
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<p><a name="index-TAmode-2763"></a><br><dt><code>TAmode</code><dd>“Tetra Accumulator” mode represents a sixteen-byte signed accumulator.
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The default format is “s64.63”.
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<p><a name="index-UHAmode-2764"></a><br><dt><code>UHAmode</code><dd>“Unsigned Half-Accumulator” mode represents a two-byte unsigned accumulator.
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The default format is “8.8”.
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<p><a name="index-USAmode-2765"></a><br><dt><code>USAmode</code><dd>“Unsigned Single Accumulator” mode represents a four-byte unsigned
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accumulator. The default format is “16.16”.
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<p><a name="index-UDAmode-2766"></a><br><dt><code>UDAmode</code><dd>“Unsigned Double Accumulator” mode represents an eight-byte unsigned
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accumulator. The default format is “32.32”.
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<p><a name="index-UTAmode-2767"></a><br><dt><code>UTAmode</code><dd>“Unsigned Tetra Accumulator” mode represents a sixteen-byte unsigned
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accumulator. The default format is “64.64”.
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<p><a name="index-CCmode-2768"></a><br><dt><code>CCmode</code><dd>“Condition Code” mode represents the value of a condition code, which
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is a machine-specific set of bits used to represent the result of a
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comparison operation. Other machine-specific modes may also be used for
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the condition code. These modes are not used on machines that use
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<code>cc0</code> (see <a href="Condition-Code.html#Condition-Code">Condition Code</a>).
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<p><a name="index-BLKmode-2769"></a><br><dt><code>BLKmode</code><dd>“Block” mode represents values that are aggregates to which none of
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the other modes apply. In RTL, only memory references can have this mode,
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and only if they appear in string-move or vector instructions. On machines
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which have no such instructions, <code>BLKmode</code> will not appear in RTL.
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<p><a name="index-VOIDmode-2770"></a><br><dt><code>VOIDmode</code><dd>Void mode means the absence of a mode or an unspecified mode.
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For example, RTL expressions of code <code>const_int</code> have mode
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<code>VOIDmode</code> because they can be taken to have whatever mode the context
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requires. In debugging dumps of RTL, <code>VOIDmode</code> is expressed by
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the absence of any mode.
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<p><a name="index-QCmode-2771"></a><a name="index-HCmode-2772"></a><a name="index-SCmode-2773"></a><a name="index-DCmode-2774"></a><a name="index-XCmode-2775"></a><a name="index-TCmode-2776"></a><br><dt><code>QCmode, HCmode, SCmode, DCmode, XCmode, TCmode</code><dd>These modes stand for a complex number represented as a pair of floating
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point values. The floating point values are in <code>QFmode</code>,
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<code>HFmode</code>, <code>SFmode</code>, <code>DFmode</code>, <code>XFmode</code>, and
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<code>TFmode</code>, respectively.
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<p><a name="index-CQImode-2777"></a><a name="index-CHImode-2778"></a><a name="index-CSImode-2779"></a><a name="index-CDImode-2780"></a><a name="index-CTImode-2781"></a><a name="index-COImode-2782"></a><br><dt><code>CQImode, CHImode, CSImode, CDImode, CTImode, COImode</code><dd>These modes stand for a complex number represented as a pair of integer
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values. The integer values are in <code>QImode</code>, <code>HImode</code>,
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<code>SImode</code>, <code>DImode</code>, <code>TImode</code>, and <code>OImode</code>,
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respectively.
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<p><a name="index-BND32mode-2783"></a><a name="index-BND64mode-2784"></a><br><dt><code>BND32mode BND64mode</code><dd>These modes stand for bounds for pointer of 32 and 64 bit size respectively.
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Mode size is double pointer mode size.
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</dl>
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<p>The machine description defines <code>Pmode</code> as a C macro which expands
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into the machine mode used for addresses. Normally this is the mode
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whose size is <code>BITS_PER_WORD</code>, <code>SImode</code> on 32-bit machines.
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<p>The only modes which a machine description <i>must</i> support are
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<code>QImode</code>, and the modes corresponding to <code>BITS_PER_WORD</code>,
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<code>FLOAT_TYPE_SIZE</code> and <code>DOUBLE_TYPE_SIZE</code>.
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The compiler will attempt to use <code>DImode</code> for 8-byte structures and
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unions, but this can be prevented by overriding the definition of
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<code>MAX_FIXED_MODE_SIZE</code>. Alternatively, you can have the compiler
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use <code>TImode</code> for 16-byte structures and unions. Likewise, you can
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arrange for the C type <code>short int</code> to avoid using <code>HImode</code>.
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<p><a name="index-mode-classes-2785"></a>Very few explicit references to machine modes remain in the compiler and
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these few references will soon be removed. Instead, the machine modes
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are divided into mode classes. These are represented by the enumeration
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type <code>enum mode_class</code> defined in <samp><span class="file">machmode.h</span></samp>. The possible
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mode classes are:
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<a name="index-MODE_005fINT-2786"></a>
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<dl><dt><code>MODE_INT</code><dd>Integer modes. By default these are <code>BImode</code>, <code>QImode</code>,
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<code>HImode</code>, <code>SImode</code>, <code>DImode</code>, <code>TImode</code>, and
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<code>OImode</code>.
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<p><a name="index-MODE_005fPARTIAL_005fINT-2787"></a><br><dt><code>MODE_PARTIAL_INT</code><dd>The “partial integer” modes, <code>PQImode</code>, <code>PHImode</code>,
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<code>PSImode</code> and <code>PDImode</code>.
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<p><a name="index-MODE_005fFLOAT-2788"></a><br><dt><code>MODE_FLOAT</code><dd>Floating point modes. By default these are <code>QFmode</code>,
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<code>HFmode</code>, <code>TQFmode</code>, <code>SFmode</code>, <code>DFmode</code>,
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<code>XFmode</code> and <code>TFmode</code>.
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<p><a name="index-MODE_005fDECIMAL_005fFLOAT-2789"></a><br><dt><code>MODE_DECIMAL_FLOAT</code><dd>Decimal floating point modes. By default these are <code>SDmode</code>,
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<code>DDmode</code> and <code>TDmode</code>.
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<p><a name="index-MODE_005fFRACT-2790"></a><br><dt><code>MODE_FRACT</code><dd>Signed fractional modes. By default these are <code>QQmode</code>, <code>HQmode</code>,
|
||
|
|
<code>SQmode</code>, <code>DQmode</code> and <code>TQmode</code>.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fUFRACT-2791"></a><br><dt><code>MODE_UFRACT</code><dd>Unsigned fractional modes. By default these are <code>UQQmode</code>, <code>UHQmode</code>,
|
||
|
|
<code>USQmode</code>, <code>UDQmode</code> and <code>UTQmode</code>.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fACCUM-2792"></a><br><dt><code>MODE_ACCUM</code><dd>Signed accumulator modes. By default these are <code>HAmode</code>,
|
||
|
|
<code>SAmode</code>, <code>DAmode</code> and <code>TAmode</code>.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fUACCUM-2793"></a><br><dt><code>MODE_UACCUM</code><dd>Unsigned accumulator modes. By default these are <code>UHAmode</code>,
|
||
|
|
<code>USAmode</code>, <code>UDAmode</code> and <code>UTAmode</code>.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fCOMPLEX_005fINT-2794"></a><br><dt><code>MODE_COMPLEX_INT</code><dd>Complex integer modes. (These are not currently implemented).
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fCOMPLEX_005fFLOAT-2795"></a><br><dt><code>MODE_COMPLEX_FLOAT</code><dd>Complex floating point modes. By default these are <code>QCmode</code>,
|
||
|
|
<code>HCmode</code>, <code>SCmode</code>, <code>DCmode</code>, <code>XCmode</code>, and
|
||
|
|
<code>TCmode</code>.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fFUNCTION-2796"></a><br><dt><code>MODE_FUNCTION</code><dd>Algol or Pascal function variables including a static chain.
|
||
|
|
(These are not currently implemented).
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fCC-2797"></a><br><dt><code>MODE_CC</code><dd>Modes representing condition code values. These are <code>CCmode</code> plus
|
||
|
|
any <code>CC_MODE</code> modes listed in the <samp><var>machine</var><span class="file">-modes.def</span></samp>.
|
||
|
|
See <a href="Jump-Patterns.html#Jump-Patterns">Jump Patterns</a>,
|
||
|
|
also see <a href="Condition-Code.html#Condition-Code">Condition Code</a>.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fPOINTER_005fBOUNDS-2798"></a><br><dt><code>MODE_POINTER_BOUNDS</code><dd>Pointer bounds modes. Used to represent values of pointer bounds type.
|
||
|
|
Operations in these modes may be executed as NOPs depending on hardware
|
||
|
|
features and environment setup.
|
||
|
|
|
||
|
|
<p><a name="index-MODE_005fRANDOM-2799"></a><br><dt><code>MODE_RANDOM</code><dd>This is a catchall mode class for modes which don't fit into the above
|
||
|
|
classes. Currently <code>VOIDmode</code> and <code>BLKmode</code> are in
|
||
|
|
<code>MODE_RANDOM</code>.
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<p>Here are some C macros that relate to machine modes:
|
||
|
|
|
||
|
|
|
||
|
|
<a name="index-GET_005fMODE-2800"></a>
|
||
|
|
<dl><dt><code>GET_MODE (</code><var>x</var><code>)</code><dd>Returns the machine mode of the RTX <var>x</var>.
|
||
|
|
|
||
|
|
<p><a name="index-PUT_005fMODE-2801"></a><br><dt><code>PUT_MODE (</code><var>x</var><code>, </code><var>newmode</var><code>)</code><dd>Alters the machine mode of the RTX <var>x</var> to be <var>newmode</var>.
|
||
|
|
|
||
|
|
<p><a name="index-NUM_005fMACHINE_005fMODES-2802"></a><br><dt><code>NUM_MACHINE_MODES</code><dd>Stands for the number of machine modes available on the target
|
||
|
|
machine. This is one greater than the largest numeric value of any
|
||
|
|
machine mode.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fNAME-2803"></a><br><dt><code>GET_MODE_NAME (</code><var>m</var><code>)</code><dd>Returns the name of mode <var>m</var> as a string.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fCLASS-2804"></a><br><dt><code>GET_MODE_CLASS (</code><var>m</var><code>)</code><dd>Returns the mode class of mode <var>m</var>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fWIDER_005fMODE-2805"></a><br><dt><code>GET_MODE_WIDER_MODE (</code><var>m</var><code>)</code><dd>Returns the next wider natural mode. For example, the expression
|
||
|
|
<code>GET_MODE_WIDER_MODE (QImode)</code> returns <code>HImode</code>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fSIZE-2806"></a><br><dt><code>GET_MODE_SIZE (</code><var>m</var><code>)</code><dd>Returns the size in bytes of a datum of mode <var>m</var>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fBITSIZE-2807"></a><br><dt><code>GET_MODE_BITSIZE (</code><var>m</var><code>)</code><dd>Returns the size in bits of a datum of mode <var>m</var>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fIBIT-2808"></a><br><dt><code>GET_MODE_IBIT (</code><var>m</var><code>)</code><dd>Returns the number of integral bits of a datum of fixed-point mode <var>m</var>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fFBIT-2809"></a><br><dt><code>GET_MODE_FBIT (</code><var>m</var><code>)</code><dd>Returns the number of fractional bits of a datum of fixed-point mode <var>m</var>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fMASK-2810"></a><br><dt><code>GET_MODE_MASK (</code><var>m</var><code>)</code><dd>Returns a bitmask containing 1 for all bits in a word that fit within
|
||
|
|
mode <var>m</var>. This macro can only be used for modes whose bitsize is
|
||
|
|
less than or equal to <code>HOST_BITS_PER_INT</code>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fALIGNMENT-2811"></a><br><dt><code>GET_MODE_ALIGNMENT (</code><var>m</var><code>)</code><dd>Return the required alignment, in bits, for an object of mode <var>m</var>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fUNIT_005fSIZE-2812"></a><br><dt><code>GET_MODE_UNIT_SIZE (</code><var>m</var><code>)</code><dd>Returns the size in bytes of the subunits of a datum of mode <var>m</var>.
|
||
|
|
This is the same as <code>GET_MODE_SIZE</code> except in the case of complex
|
||
|
|
modes. For them, the unit size is the size of the real or imaginary
|
||
|
|
part.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fMODE_005fNUNITS-2813"></a><br><dt><code>GET_MODE_NUNITS (</code><var>m</var><code>)</code><dd>Returns the number of units contained in a mode, i.e.,
|
||
|
|
<code>GET_MODE_SIZE</code> divided by <code>GET_MODE_UNIT_SIZE</code>.
|
||
|
|
|
||
|
|
<p><a name="index-GET_005fCLASS_005fNARROWEST_005fMODE-2814"></a><br><dt><code>GET_CLASS_NARROWEST_MODE (</code><var>c</var><code>)</code><dd>Returns the narrowest mode in mode class <var>c</var>.
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<p>The following 3 variables are defined on every target. They can be
|
||
|
|
used to allocate buffers that are guaranteed to be large enough to
|
||
|
|
hold any value that can be represented on the target. The first two
|
||
|
|
can be overridden by defining them in the target's mode.def file,
|
||
|
|
however, the value must be a constant that can determined very early
|
||
|
|
in the compilation process. The third symbol cannot be overridden.
|
||
|
|
|
||
|
|
|
||
|
|
<a name="index-BITS_005fPER_005fUNIT-2815"></a>
|
||
|
|
<dl><dt><code>BITS_PER_UNIT</code><dd>The number of bits in an addressable storage unit (byte). If you do
|
||
|
|
not define this, the default is 8.
|
||
|
|
|
||
|
|
<p><a name="index-MAX_005fBITSIZE_005fMODE_005fANY_005fINT-2816"></a><br><dt><code>MAX_BITSIZE_MODE_ANY_INT</code><dd>The maximum bitsize of any mode that is used in integer math. This
|
||
|
|
should be overridden by the target if it uses large integers as
|
||
|
|
containers for larger vectors but otherwise never uses the contents to
|
||
|
|
compute integer values.
|
||
|
|
|
||
|
|
<p><a name="index-MAX_005fBITSIZE_005fMODE_005fANY_005fMODE-2817"></a><br><dt><code>MAX_BITSIZE_MODE_ANY_MODE</code><dd>The bitsize of the largest mode on the target.
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<p><a name="index-byte_005fmode-2818"></a><a name="index-word_005fmode-2819"></a>The global variables <code>byte_mode</code> and <code>word_mode</code> contain modes
|
||
|
|
whose classes are <code>MODE_INT</code> and whose bitsizes are either
|
||
|
|
<code>BITS_PER_UNIT</code> or <code>BITS_PER_WORD</code>, respectively. On 32-bit
|
||
|
|
machines, these are <code>QImode</code> and <code>SImode</code>, respectively.
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|