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Documentation for the new non-overflow and exact keywords. 

llvm-svn: 76495
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Dan Gohman 2009-07-20 22:41:19 +00:00
parent c0656de03d
commit b07de44d5a
1 changed files with 26 additions and 11 deletions
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29
llvm/docs/LangRef.html
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@ -2601,6 +2601,8 @@ Instruction</a> </div>
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = add &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = signed add &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = unsigned add &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
@ -2620,6 +2622,10 @@ Instruction</a> </div>
<p>Because LLVM integers use a two's complement representation, this instruction
is appropriate for both signed and unsigned integers.</p>
<p>If the <tt>signed</tt> and/or <tt>unsigned</tt> keywords are present,
the behavior of the <tt>add</tt> is undefined if signed and/or unsigned
overflow, respectively, occurs.</p>
<h5>Example:</h5>
<pre>
&lt;result&gt; = add i32 4, %var <i>; yields {i32}:result = 4 + %var</i>
@ -2667,6 +2673,8 @@ Instruction</a> </div>
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = sub &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = signed sub &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = unsigned sub &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
@ -2692,6 +2700,10 @@ Instruction</a> </div>
<p>Because LLVM integers use a two's complement representation, this instruction
is appropriate for both signed and unsigned integers.</p>
<p>If the <tt>signed</tt> and/or <tt>unsigned</tt> keywords are present,
the behavior of the <tt>sub</tt> is undefined if signed and/or unsigned
overflow, respectively, occurs.</p>
<h5>Example:</h5>
<pre>
&lt;result&gt; = sub i32 4, %var <i>; yields {i32}:result = 4 - %var</i>
@ -2746,6 +2758,8 @@ Instruction</a> </div>
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = mul &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = signed mul &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = unsigned mul &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
@ -2770,6 +2784,10 @@ Instruction</a> </div>
be sign-extended or zero-extended as appropriate to the width of the full
product.</p>
<p>If the <tt>signed</tt> and/or <tt>unsigned</tt> keywords are present,
the behavior of the <tt>mul</tt> is undefined if signed and/or unsigned
overflow, respectively, occurs.</p>
<h5>Example:</h5>
<pre>
&lt;result&gt; = mul i32 4, %var <i>; yields {i32}:result = 4 * %var</i>
@ -2850,6 +2868,7 @@ Instruction</a> </div>
<h5>Syntax:</h5>
<pre>
&lt;result&gt; = sdiv &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
&lt;result&gt; = exact sdiv &lt;ty&gt; &lt;op1&gt;, &lt;op2&gt; <i>; yields {ty}:result</i>
</pre>
<h5>Overview:</h5>
@ -2871,6 +2890,9 @@ Instruction</a> </div>
undefined behavior; this is a rare case, but can occur, for example, by doing
a 32-bit division of -2147483648 by -1.</p>
<p>If the <tt>exact</tt> keyword is present, the result of the <tt>sdiv</tt>
is undefined if the result would be rounded or if overflow occurs.</p>
<h5>Example:</h5>
<pre>
&lt;result&gt; = sdiv i32 4, %var <i>; yields {i32}:result = 4 / %var</i>
@ -3912,13 +3934,6 @@ entry:
}
</pre>
<p>Note that it is undefined to access an array out of bounds: array and pointer
indexes must always be within the defined bounds of the array type when
accessed with an instruction that dereferences the pointer (e.g. a load or
store instruction). The one exception for this rule is zero length arrays.
These arrays are defined to be accessible as variable length arrays, which
requires access beyond the zero'th element.</p>
<p>The getelementptr instruction is often confusing. For some more insight into
how it works, see <a href="GetElementPtr.html">the getelementptr FAQ</a>.</p>