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Update the LangRef documentation for llvm.ctlz and llvm.cttz to specify 

the behavior with the newly added flag for undefined results on a zero
input.

I'm terrible at documentation, so comments and suggestions welcome here.

llvm-svn: 146361
This commit is contained in:
Chandler Carruth 2011-12-12 04:36:04 +00:00
parent 026cc37e48
commit f6bb278ee8
1 changed files with 37 additions and 23 deletions
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llvm/docs/LangRef.html
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@ -7335,12 +7335,12 @@ LLVM</a>.</p>
targets support all bit widths or vector types, however.</p>
<pre>
declare i8 @llvm.ctlz.i8 (i8 &lt;src&gt;)
declare i16 @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 i256 @llvm.ctlz.i256(i256 &lt;src&gt;)
declare &lt;2 x i32&gt; @llvm.ctlz.v2i32(&lt;2 x i32&gt; &lt;src;gt)
declare i8 @llvm.ctlz.i8 (i8 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i16 @llvm.ctlz.i16 (i16 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i32 @llvm.ctlz.i32 (i32 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i64 @llvm.ctlz.i64 (i64 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i256 @llvm.ctlz.i256(i256 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declase &lt;2 x i32&gt; @llvm.ctlz.v2i32(&lt;2 x i32&gt; &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
</pre>
<h5>Overview:</h5>
@ -7348,15 +7348,22 @@ LLVM</a>.</p>
leading zeros in a variable.</p>
<h5>Arguments:</h5>
<p>The only argument is the value to be counted. The argument may be of any
integer type, or any vector type with integer element type.
The return type must match the argument type.</p>
<p>The first argument is the value to be counted. This argument may be of any
integer type, or a vectory with integer element type. The return type
must match the first argument type.</p>
<p>The second argument must be a constant and is a flag to indicate whether the
intrinsic should ensure that a zero as the first argument produces a defined
result. Historically some architectures did not provide a defined result for
zero values as efficiently, and many algorithms are now predicated on
avoiding zero-value inputs.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant)
zeros in a variable, or within each element of the vector if the operation
is of vector type. If the src == 0 then the result is the size in bits of
the type of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p>
zeros in a variable, or within each element of the vector.
If <tt>src == 0</tt> then the result is the size in bits of the type of
<tt>src</tt> if <tt>is_zero_undef == 0</tt> and <tt>undef</tt> otherwise.
For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p>
</div>
@ -7373,12 +7380,12 @@ LLVM</a>.</p>
support all bit widths or vector types, however.</p>
<pre>
declare i8 @llvm.cttz.i8 (i8 &lt;src&gt;)
declare i16 @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 i256 @llvm.cttz.i256(i256 &lt;src&gt;)
declase &lt;2 x i32&gt; @llvm.cttz.v2i32(&lt;2 x i32&gt; &lt;src&gt;)
declare i8 @llvm.cttz.i8 (i8 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i16 @llvm.cttz.i16 (i16 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i32 @llvm.cttz.i32 (i32 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i64 @llvm.cttz.i64 (i64 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declare i256 @llvm.cttz.i256(i256 &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
declase &lt;2 x i32&gt; @llvm.cttz.v2i32(&lt;2 x i32&gt; &lt;src&gt;, i1 &lt;is_zero_undef&gt;)
</pre>
<h5>Overview:</h5>
@ -7386,15 +7393,22 @@ LLVM</a>.</p>
trailing zeros.</p>
<h5>Arguments:</h5>
<p>The only argument is the value to be counted. The argument may be of any
integer type, or a vectory with integer element type.. The return type
must match the argument type.</p>
<p>The first argument is the value to be counted. This argument may be of any
integer type, or a vectory with integer element type. The return type
must match the first argument type.</p>
<p>The second argument must be a constant and is a flag to indicate whether the
intrinsic should ensure that a zero as the first argument produces a defined
result. Historically some architectures did not provide a defined result for
zero values as efficiently, and many algorithms are now predicated on
avoiding zero-value inputs.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant)
zeros in a variable, or within each element of a vector.
If the src == 0 then the result is the size in bits of
the type of src. For example, <tt>llvm.cttz(2) = 1</tt>.</p>
If <tt>src == 0</tt> then the result is the size in bits of the type of
<tt>src</tt> if <tt>is_zero_undef == 0</tt> and <tt>undef</tt> otherwise.
For example, <tt>llvm.cttz(2) = 1</tt>.</p>
</div>