add a note
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33904 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/ProgrammersManual.html b/docs/ProgrammersManual.html
index 1d5ad0e..c4fedbf 100644
--- a/docs/ProgrammersManual.html
+++ b/docs/ProgrammersManual.html
@@ -797,6 +797,33 @@
itself (which would waste space for elements that aren't in the container).
vector is also useful when interfacing with code that expects vectors :).
</p>
+
+<p>One worthwhile note about std::vector: avoid code like this:</p>
+
+<div class="doc_code">
+<pre>
+for ( ... ) {
+ std::vector<foo> V;
+ use V;
+}
+</pre>
+</div>
+
+<p>Instead, write this as:</p>
+
+<div class="doc_code">
+<pre>
+std::vector<foo> V;
+for ( ... ) {
+ use V;
+ V.clear();
+}
+</pre>
+</div>
+
+<p>Doing so will save (at least) one heap allocation and free per iteration of
+the loop.</p>
+
</div>
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