LangRef.html

aggressive transformations, so the value returned may not that of the obvious
source-language caller.
</p>
</div>

<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="int_os">Operating System Intrinsics</a>
</div>

<div class="doc_text">
<p>
These intrinsics are provided by LLVM to support the implementation of
operating system level code.
</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_readport">'<tt>llvm.readport</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call &lt;integer type&gt; (&lt;integer type&gt;)* %llvm.readport (&lt;integer type&gt; &lt;address&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.readport</tt>' intrinsic reads data from the specified hardware
I/O port.
</p>

<h5>Arguments:</h5>

<p>
The argument to this intrinsic indicates the hardware I/O address from which
to read the data.  The address is in the hardware I/O address namespace (as
opposed to being a memory location for memory mapped I/O).
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.readport</tt>' intrinsic reads data from the hardware I/O port
specified by <i>address</i> and returns the value.  The address and return
value must be integers, but the size is dependent upon the platform upon which
the program is code generated.  For example, on x86, the address must be an
unsigned 16 bit value, and the return value must be 8, 16, or 32 bits.
</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_writeport">'<tt>llvm.writeport</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call void (&lt;integer type&gt;, &lt;integer type&gt;)* %llvm.writeport (&lt;integer type&gt; &lt;value&gt;, &lt;integer type&gt; &lt;address&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.writeport</tt>' intrinsic writes data to the specified hardware
I/O port.
</p>

<h5>Arguments:</h5>

<p>
The first argument to this intrinsic indicates the hardware I/O address to
which data should be written.  The address is in the hardware I/O address
namespace (as opposed to being a memory location for memory mapped I/O).
</p>

<p>
The second argument is the value to write to the I/O port.
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.writeport</tt>' intrinsic writes <i>value</i> to the I/O port
specified by <i>address</i>.  The address and value must be integers, but the
size is dependent upon the platform upon which the program is code generated.
For example, on x86, the address must be an unsigned 16 bit value, and the
value written must be 8, 16, or 32 bits in length.
</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_readio">'<tt>llvm.readio</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call &lt;integer type&gt; (&lt;integer type&gt;)* %llvm.readio (&lt;integer type&gt; &lt;address&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
address.
</p>

<h5>Arguments:</h5>

<p>
The argument to this intrinsic indicates the memory address from which to read
the data.
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.readio</tt>' intrinsic reads data from a memory mapped I/O
location specified by <i>address</i> and returns the value.  The address and
return value must be integers, but the size allowed for each is dependent upon
the platform upon which the program is code generated.
</p>

<p>
This intrinsic ensures that the I/O data read occurs in instruction order in
relation to other I/O data reads and writes (as opposed to a normal load, where
hardware scheduling can re-arrange the actual memory accesses to occur out of
order).
</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_writeio">'<tt>llvm.writeio</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call void (&lt;integer type&gt;, &lt;integer type&gt;)* %llvm.writeio (&lt;integer type&gt; &lt;value&gt;, &lt;integer type&gt; &lt;address&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.writeio</tt>' intrinsic writes data to the specified memory
mapped I/O address.
</p>

<h5>Arguments:</h5>

<p>
The first argument to this intrinsic indicates the memory address to which data
should be written.
</p>

<p>
The second argument is the value to write to the memory mapped I/O location.
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.writeio</tt>' intrinsic writes <i>value</i> to the memory mapped
I/O address specified by <i>address</i>.  The address and value must be
integers, but the size is dependent upon the platform upon which the program is
code generated.
</p>

<p>
This intrinsic ensures that the I/O data write occurs in instruction order in
relation to other I/O data reads and writes (as opposed to a normal store,
where hardware scheduling can re-arrange the actual memory accesses to occur
out of order).
</p>

</div>


<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="int_libc">Standard C Library Intrinsics</a>
</div>

<div class="doc_text">
<p>
LLVM provides intrinsics for a few important standard C library functions.
These intrinsics allow source-language front-ends to pass information about the
alignment of the pointer arguments to the code generator, providing opportunity
for more efficient code generation.
</p>

</div>

<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_memcpy">'<tt>llvm.memcpy</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call void (sbyte*, sbyte*, uint, uint)* %llvm.memcpy(sbyte* &lt;dest&gt;, sbyte* &lt;src&gt;,
                                                       uint &lt;len&gt;, uint &lt;align&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
location to the destination location.
</p>

<p>
Note that, unlike the standard libc function, the <tt>llvm.memcpy</tt> intrinsic
does not return a value, and takes an extra alignment argument.
</p>

<h5>Arguments:</h5>

<p>
The first argument is a pointer to the destination, the second is a pointer to
the source.  The third argument is an (arbitrarily sized) integer argument
specifying the number of bytes to copy, and the fourth argument is the alignment
of the source and destination locations.
</p>

<p>
If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the size of the copy is a multiple of the alignment
and that both the source and destination pointers are aligned to that boundary.
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.memcpy</tt>' intrinsic copies a block of memory from the source
location to the destination location, which are not allowed to overlap.  It
copies "len" bytes of memory over.  If the argument is known to be aligned to
some boundary, this can be specified as the fourth argument, otherwise it should
be set to 0 or 1.
</p>
</div>


<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_memmove">'<tt>llvm.memmove</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call void (sbyte*, sbyte*, uint, uint)* %llvm.memmove(sbyte* &lt;dest&gt;, sbyte* &lt;src&gt;,
                                                       uint &lt;len&gt;, uint &lt;align&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.memmove</tt>' intrinsic moves a block of memory from the source
location to the destination location. It is similar to the '<tt>llvm.memcpy</tt>' 
intrinsic but allows the two memory locations to overlap.
</p>

<p>
Note that, unlike the standard libc function, the <tt>llvm.memmove</tt> intrinsic
does not return a value, and takes an extra alignment argument.
</p>

<h5>Arguments:</h5>

<p>
The first argument is a pointer to the destination, the second is a pointer to
the source.  The third argument is an (arbitrarily sized) integer argument
specifying the number of bytes to copy, and the fourth argument is the alignment
of the source and destination locations.
</p>

<p>
If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the size of the copy is a multiple of the alignment
and that both the source and destination pointers are aligned to that boundary.
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.memmove</tt>' intrinsic copies a block of memory from the source
location to the destination location, which may overlap.  It
copies "len" bytes of memory over.  If the argument is known to be aligned to
some boundary, this can be specified as the fourth argument, otherwise it should
be set to 0 or 1.
</p>
</div>


<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
  <a name="i_memset">'<tt>llvm.memset</tt>' Intrinsic</a>
</div>

<div class="doc_text">

<h5>Syntax:</h5>
<pre>
  call void (sbyte*, ubyte, uint, uint)* %llvm.memset(sbyte* &lt;dest&gt;, ubyte &lt;val&gt;,
                                                      uint &lt;len&gt;, uint &lt;align&gt;)
</pre>

<h5>Overview:</h5>

<p>
The '<tt>llvm.memset</tt>' intrinsic fills a block of memory with a particular
byte value.
</p>

<p>
Note that, unlike the standard libc function, the <tt>llvm.memset</tt> intrinsic
does not return a value, and takes an extra alignment argument.
</p>

<h5>Arguments:</h5>

<p>
The first argument is a pointer to the destination to fill, the second is the
byte value to fill it with, the third argument is an (arbitrarily sized) integer
argument specifying the number of bytes to fill, and the fourth argument is the
known alignment of destination location.
</p>

<p>
If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the size of the copy is a multiple of the alignment
and that the destination pointer is aligned to that boundary.
</p>

<h5>Semantics:</h5>

<p>
The '<tt>llvm.memset</tt>' intrinsic fills "len" bytes of memory starting at the
destination location.  If the argument is known to be aligned to some boundary,
this can be specified as the fourth argument, otherwise it should be set to 0 or
1.
</p>
</div>


<!-- ======================================================================= -->
<div class="doc_subsection">
  <a name="int_debugger">Debugger Intrinsics</a>
</div>

<div class="doc_text">
<p>
The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> prefix),
are described in the <a
href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source Level
Debugging</a> document.
</p>
</div>


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