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128 lines
8.0 KiB
HTML
4 years ago
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<title>Mode Switching - GNU Compiler Collection (GCC) Internals</title>
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<link rel="up" href="Target-Macros.html#Target-Macros" title="Target Macros">
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<link rel="prev" href="Floating-Point.html#Floating-Point" title="Floating Point">
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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="Mode-Switching"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Target-Attributes.html#Target-Attributes">Target Attributes</a>,
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Previous: <a rel="previous" accesskey="p" href="Floating-Point.html#Floating-Point">Floating Point</a>,
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Up: <a rel="up" accesskey="u" href="Target-Macros.html#Target-Macros">Target Macros</a>
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<hr>
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</div>
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<h3 class="section">17.23 Mode Switching Instructions</h3>
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<p><a name="index-mode-switching-4818"></a>The following macros control mode switching optimizations:
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<div class="defun">
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— Macro: <b>OPTIMIZE_MODE_SWITCHING</b> (<var>entity</var>)<var><a name="index-OPTIMIZE_005fMODE_005fSWITCHING-4819"></a></var><br>
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<blockquote><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>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 can't put this into instruction emitting
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or <code>TARGET_MACHINE_DEPENDENT_REORG</code>.
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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></blockquote></div>
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<div class="defun">
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— Macro: <b>NUM_MODES_FOR_MODE_SWITCHING</b><var><a name="index-NUM_005fMODES_005fFOR_005fMODE_005fSWITCHING-4820"></a></var><br>
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<blockquote><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 <small class="dots">...</small> N − 1. N is used to specify that no mode
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switch is needed / supplied.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: void <b>TARGET_MODE_EMIT</b> (<var>int entity, int mode, int prev_mode, HARD_REG_SET regs_live</var>)<var><a name="index-TARGET_005fMODE_005fEMIT-4821"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: int <b>TARGET_MODE_NEEDED</b> (<var>int entity, rtx_insn *insn</var>)<var><a name="index-TARGET_005fMODE_005fNEEDED-4822"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: int <b>TARGET_MODE_AFTER</b> (<var>int entity, int mode, rtx_insn *insn</var>)<var><a name="index-TARGET_005fMODE_005fAFTER-4823"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: int <b>TARGET_MODE_ENTRY</b> (<var>int entity</var>)<var><a name="index-TARGET_005fMODE_005fENTRY-4824"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: int <b>TARGET_MODE_EXIT</b> (<var>int entity</var>)<var><a name="index-TARGET_005fMODE_005fEXIT-4825"></a></var><br>
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<blockquote><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></blockquote></div>
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<div class="defun">
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— Target Hook: int <b>TARGET_MODE_PRIORITY</b> (<var>int entity, int n</var>)<var><a name="index-TARGET_005fMODE_005fPRIORITY-4826"></a></var><br>
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<blockquote><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[</code><var>entity</var><code>] - 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 <small class="dots">...</small> <code>num_modes_for_mode_switching[</code><var>entity</var><code>] - 1</code>.
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</p></blockquote></div>
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</body></html>
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