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Clarify that shifts that are too large are undefined.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42588 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2007-10-03 21:01:14 +00:00
parent 9a7288b0c6
commit 6ccc2d579e
1 changed files with 19 additions and 3 deletions
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docs/LangRef.html
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@ -2168,18 +2168,28 @@ Instruction</a> </div>
<h5>Syntax:</h5>
<pre> &lt;result&gt; = shl &lt;ty&gt; &lt;var1&gt;, &lt;var2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
<p>The '<tt>shl</tt>' instruction returns the first operand shifted to
the left a specified number of bits.</p>
<h5>Arguments:</h5>
<p>Both arguments to the '<tt>shl</tt>' instruction must be the same <a
href="#t_integer">integer</a> type.</p>
<h5>Semantics:</h5>
<p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>.</p>
<p>The value produced is <tt>var1</tt> * 2<sup><tt>var2</tt></sup>. If
<tt>var2</tt> is (statically or dynamically) equal to or larger than the number
of bits in <tt>var1</tt>, the result is undefined.</p>
<h5>Example:</h5><pre>
&lt;result&gt; = shl i32 4, %var <i>; yields {i32}: 4 &lt;&lt; %var</i>
&lt;result&gt; = shl i32 4, 2 <i>; yields {i32}: 16</i>
&lt;result&gt; = shl i32 1, 10 <i>; yields {i32}: 1024</i>
&lt;result&gt; = shl i32 1, 32 <i>; undefined</i>
</pre>
</div>
<!-- _______________________________________________________________________ -->
@ -2199,9 +2209,11 @@ operand shifted to the right a specified number of bits with zero fill.</p>
<a href="#t_integer">integer</a> type.</p>
<h5>Semantics:</h5>
<p>This instruction always performs a logical shift right operation. The most
significant bits of the result will be filled with zero bits after the
shift.</p>
shift. If <tt>var2</tt> is (statically or dynamically) equal to or larger than
the number of bits in <tt>var1</tt>, the result is undefined.</p>
<h5>Example:</h5>
<pre>
@ -2209,6 +2221,7 @@ shift.</p>
&lt;result&gt; = lshr i32 4, 2 <i>; yields {i32}:result = 1</i>
&lt;result&gt; = lshr i8 4, 3 <i>; yields {i8}:result = 0</i>
&lt;result&gt; = lshr i8 -2, 1 <i>; yields {i8}:result = 0x7FFFFFFF </i>
&lt;result&gt; = lshr i32 1, 32 <i>; undefined</i>
</pre>
</div>
@ -2232,7 +2245,9 @@ operand shifted to the right a specified number of bits with sign extension.</p>
<h5>Semantics:</h5>
<p>This instruction always performs an arithmetic shift right operation,
The most significant bits of the result will be filled with the sign bit
of <tt>var1</tt>.</p>
of <tt>var1</tt>. If <tt>var2</tt> is (statically or dynamically) equal to or
larger than the number of bits in <tt>var1</tt>, the result is undefined.
</p>
<h5>Example:</h5>
<pre>
@ -2240,6 +2255,7 @@ of <tt>var1</tt>.</p>
&lt;result&gt; = ashr i32 4, 2 <i>; yields {i32}:result = 1</i>
&lt;result&gt; = ashr i8 4, 3 <i>; yields {i8}:result = 0</i>
&lt;result&gt; = ashr i8 -2, 1 <i>; yields {i8}:result = -1</i>
&lt;result&gt; = ashr i32 1, 32 <i>; undefined</i>
</pre>
</div>