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Document changes to bswap and bit counting intrinsics. bswap's name now
requires two types in the suffix per overloaded intrinsic naming rules.
The ctpop, cttz, and ctlz intrinsics were changed to always return i32.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35550 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer 2007-04-01 08:04:23 +00:00
parent c8d0636fef
commit 409e28f9cc
1 changed files with 49 additions and 24 deletions
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@ -3580,10 +3580,10 @@ argument.</p>
<div class="doc_text">
<p>LLVM supports the notion of an "intrinsic function". These functions have
well known names and semantics and are required to follow certain
restrictions. Overall, these instructions represent an extension mechanism for
the LLVM language that does not require changing all of the transformations in
LLVM to add to the language (or the bytecode reader/writer, the parser,
well known names and semantics and are required to follow certain restrictions.
Overall, these intrinsics represent an extension mechanism for the LLVM
language that does not require changing all of the transformations in LLVM to
add to the language (or the bytecode reader/writer, the parser,
etc...).</p>
<p>Intrinsic function names must all start with an "<tt>llvm.</tt>" prefix. This
@ -3594,9 +3594,20 @@ or invoke instructions: it is illegal to take the address of an intrinsic
function. Additionally, because intrinsic functions are part of the LLVM
language, it is required that they all be documented here if any are added.</p>
<p>Some intrinsic functions can be overloaded. That is, the intrinsic represents
a family of functions that perform the same operation but on different data
types. This is most frequent with the integer types. Since LLVM can represent
over 8 million different integer types, there is a way to declare an intrinsic
that can be overloaded based on its arguments. Such intrinsics will have the
names of the arbitrary types encoded into the intrinsic function name, each
preceded by a period. For example, the <tt>llvm.ctpop</tt> function can take an
integer of any width. This leads to a family of functions such as
<tt>i32 @llvm.ctpop.i8(i8 %val)</tt> and <tt>i32 @llvm.ctpop.i29(i29 %val)</tt>.
</p>
<p>To learn how to add an intrinsic function, please see the <a
href="ExtendingLLVM.html">Extending LLVM Guide</a>.
<p>To learn how to add an intrinsic function, please see the
<a href="ExtendingLLVM.html">Extending LLVM Guide</a>.
</p>
</div>
@ -4421,29 +4432,34 @@ These allow efficient code generation for some algorithms.
<div class="doc_text">
<h5>Syntax:</h5>
<p>This is an overloaded intrinsic function. You can use bswap on any integer
type that is an even number of bytes (i.e. BitWidth % 16 == 0). Note the suffix
that includes the type for the result and the operand.
<pre>
declare i16 @llvm.bswap.i16(i16 &lt;id&gt;)
declare i32 @llvm.bswap.i32(i32 &lt;id&gt;)
declare i64 @llvm.bswap.i64(i64 &lt;id&gt;)
declare i16 @llvm.bswap.i16.i16(i16 &lt;id&gt;)
declare i32 @llvm.bswap.i32.i32(i32 &lt;id&gt;)
declare i64 @llvm.bswap.i64.i32(i64 &lt;id&gt;)
</pre>
<h5>Overview:</h5>
<p>
The '<tt>llvm.bwsap</tt>' family of intrinsics is used to byteswap a 16, 32 or
64 bit quantity. These are useful for performing operations on data that is not
in the target's native byte order.
The '<tt>llvm.bwsap</tt>' family of intrinsics is used to byteswap integer
values with an even number of bytes (positive multiple of 16 bits). These are
useful for performing operations on data that is not in the target's native
byte order.
</p>
<h5>Semantics:</h5>
<p>
The <tt>llvm.bswap.16</tt> intrinsic returns an i16 value that has the high
The <tt>llvm.bswap.16.i16</tt> intrinsic returns an i16 value that has the high
and low byte of the input i16 swapped. Similarly, the <tt>llvm.bswap.i32</tt>
intrinsic returns an i32 value that has the four bytes of the input i32
swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the returned
i32 will have its bytes in 3, 2, 1, 0 order. The <tt>llvm.bswap.i64</tt>
intrinsic extends this concept to 64 bits.
i32 will have its bytes in 3, 2, 1, 0 order. The <tt>llvm.bswap.i48.i48</tt>,
<tt>llvm.bswap.i64.i64</tt> and other intrinsics extend this concept to
additional even-byte lengths (6 bytes, 8 bytes and more, respectively).
</p>
</div>
@ -4456,11 +4472,14 @@ intrinsic extends this concept to 64 bits.
<div class="doc_text">
<h5>Syntax:</h5>
<p>This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit
width. Not all targets support all bit widths however.
<pre>
declare i8 @llvm.ctpop.i8 (i8 &lt;src&gt;)
declare i16 @llvm.ctpop.i16(i16 &lt;src&gt;)
declare i32 @llvm.ctpop.i8 (i8 &lt;src&gt;)
declare i32 @llvm.ctpop.i16(i16 &lt;src&gt;)
declare i32 @llvm.ctpop.i32(i32 &lt;src&gt;)
declare i64 @llvm.ctpop.i64(i64 &lt;src&gt;)
declare i32 @llvm.ctpop.i64(i64 &lt;src&gt;)
declare i32 @llvm.ctpop.i256(i256 &lt;src&gt;)
</pre>
<h5>Overview:</h5>
@ -4492,11 +4511,14 @@ The '<tt>llvm.ctpop</tt>' intrinsic counts the 1's in a variable.
<div class="doc_text">
<h5>Syntax:</h5>
<p>This is an overloaded intrinsic. You can use <tt>llvm.ctlz</tt> on any
integer bit width. Not all targets support all bit widths however.
<pre>
declare i8 @llvm.ctlz.i8 (i8 &lt;src&gt;)
declare i16 @llvm.ctlz.i16(i16 &lt;src&gt;)
declare i32 @llvm.ctlz.i8 (i8 &lt;src&gt;)
declare i32 @llvm.ctlz.i16(i16 &lt;src&gt;)
declare i32 @llvm.ctlz.i32(i32 &lt;src&gt;)
declare i64 @llvm.ctlz.i64(i64 &lt;src&gt;)
declare i32 @llvm.ctlz.i64(i64 &lt;src&gt;)
declare i32 @llvm.ctlz.i256(i256 &lt;src&gt;)
</pre>
<h5>Overview:</h5>
@ -4532,11 +4554,14 @@ of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.
<div class="doc_text">
<h5>Syntax:</h5>
<p>This is an overloaded intrinsic. You can use <tt>llvm.cttz</tt> on any
integer bit width. Not all targets support all bit widths however.
<pre>
declare i8 @llvm.cttz.i8 (i8 &lt;src&gt;)
declare i16 @llvm.cttz.i16(i16 &lt;src&gt;)
declare i32 @llvm.cttz.i8 (i8 &lt;src&gt;)
declare i32 @llvm.cttz.i16(i16 &lt;src&gt;)
declare i32 @llvm.cttz.i32(i32 &lt;src&gt;)
declare i64 @llvm.cttz.i64(i64 &lt;src&gt;)
declare i32 @llvm.cttz.i64(i64 &lt;src&gt;)
declare i32 @llvm.cttz.i256(i256 &lt;src&gt;)
</pre>
<h5>Overview:</h5>