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141 lines
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141 lines
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<title>poly_int (GNU Compiler Collection (GCC) Internals)</title>
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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="Overview-of-poly_005fint.html#Overview-of-poly_005fint" rel="next" title="Overview of poly_int">
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<a name="poly_005fint"></a>
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<div class="header">
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<p>
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Next: <a href="GENERIC.html#GENERIC" accesskey="n" rel="next">GENERIC</a>, Previous: <a href="Passes.html#Passes" accesskey="p" rel="prev">Passes</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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="Sizes-and-offsets-as-runtime-invariants"></a>
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<h2 class="chapter">10 Sizes and offsets as runtime invariants</h2>
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<a name="index-polynomial-integers"></a>
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<a name="index-poly_005fint"></a>
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<p>GCC allows the size of a hardware register to be a runtime invariant
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rather than a compile-time constant. This in turn means that various
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sizes and offsets must also be runtime invariants rather than
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compile-time constants, such as:
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</p>
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<ul>
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<li> the size of a general <code>machine_mode</code> (see <a href="Machine-Modes.html#Machine-Modes">Machine Modes</a>);
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</li><li> the size of a spill slot;
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</li><li> the offset of something within a stack frame;
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</li><li> the number of elements in a vector;
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</li><li> the size and offset of a <code>mem</code> rtx (see <a href="Regs-and-Memory.html#Regs-and-Memory">Regs and Memory</a>); and
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</li><li> the byte offset in a <code>subreg</code> rtx (see <a href="Regs-and-Memory.html#Regs-and-Memory">Regs and Memory</a>).
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</li></ul>
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<p>The motivating example is the Arm SVE ISA, whose vector registers can be
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any multiple of 128 bits between 128 and 2048 inclusive. The compiler
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normally produces code that works for all SVE register sizes, with the
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actual size only being known at runtime.
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</p>
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<p>GCC’s main representation of such runtime invariants is the
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<code>poly_int</code> class. This chapter describes what <code>poly_int</code>
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does, lists the available operations, and gives some general
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usage guidelines.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Overview-of-poly_005fint.html#Overview-of-poly_005fint" accesskey="1">Overview of <code>poly_int</code></a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Consequences-of-using-poly_005fint.html#Consequences-of-using-poly_005fint" accesskey="2">Consequences of using <code>poly_int</code></a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Comparisons-involving-poly_005fint.html#Comparisons-involving-poly_005fint" accesskey="3">Comparisons involving <code>poly_int</code></a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Arithmetic-on-poly_005fints.html#Arithmetic-on-poly_005fints" accesskey="4">Arithmetic on <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Alignment-of-poly_005fints.html#Alignment-of-poly_005fints" accesskey="5">Alignment of <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" accesskey="6">Computing bounds on <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Converting-poly_005fints.html#Converting-poly_005fints" accesskey="7">Converting <code>poly_int</code>s</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Miscellaneous-poly_005fint-routines.html#Miscellaneous-poly_005fint-routines" accesskey="8">Miscellaneous <code>poly_int</code> routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Guidelines-for-using-poly_005fint.html#Guidelines-for-using-poly_005fint" accesskey="9">Guidelines for using <code>poly_int</code></a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="GENERIC.html#GENERIC" accesskey="n" rel="next">GENERIC</a>, Previous: <a href="Passes.html#Passes" accesskey="p" rel="prev">Passes</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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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