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Update the vectorizer docs.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167688 91177308-0d34-0410-b5e6-96231b3b80d8
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Nadav Rotem 2012-11-11 06:47:51 +00:00
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@ -473,15 +473,31 @@ Release Notes</a>.</h1>
<b>-mllvm -force-vector-width=4</b>.
The default value is <b>0</b> which means auto-select.
<br/>
We can now vectorize this code:
We can now vectorize this function:
<pre class="doc_code">
for (i=0; i&lt;n; i++) {
a[i] = b[i+1] + c[i+3] + i;
sum += d[i];
unsigned sum_arrays(int *A, int *B, int start, int end) {
unsigned sum = 0;
for (int i = start; i &lt; end; ++i)
sum += A[i] + B[i] + i;
return sum;
}
</pre>
We vectorize under the following loops:
<ul>
<li>The inner most loops must have a single basic block.</li>
<li>The number of iterations are known before the loop starts to execute.</li>
<li>The loop counter needs to be incrimented by one.</li>
<li>The loop trip count <b>can</b> be a variable.</li>
<li>Loops do <b>not</b> need to start at zero.</li>
<li>The induction variable can be used inside the loop.</li>
<li>Loop reductions are supported.</li>
<li>Arrays with affine access pattern do <b>not</b> need to be marked as 'noalias' and are checked at runtime.</li>
<li>...</li>
</ul>
</p>
<p>SROA - We've re-written SROA to be significantly more powerful.