[llvm-commits] [llvm] r99638 - /llvm/trunk/docs/ProgrammersManual.html
Gabor Greif
ggreif at gmail.com
Fri Mar 26 12:30:48 PDT 2010
Author: ggreif
Date: Fri Mar 26 14:30:47 2010
New Revision: 99638
URL: http://llvm.org/viewvc/llvm-project?rev=99638&view=rev
Log:
add a blurb on const versions of chain traversals and a word of caution
Modified:
llvm/trunk/docs/ProgrammersManual.html
Modified: llvm/trunk/docs/ProgrammersManual.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/ProgrammersManual.html?rev=99638&r1=99637&r2=99638&view=diff
==============================================================================
--- llvm/trunk/docs/ProgrammersManual.html (original)
+++ llvm/trunk/docs/ProgrammersManual.html Fri Mar 26 14:30:47 2010
@@ -1211,14 +1211,14 @@
<div class="doc_text">
-<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
-transparently implemented with a SmallPtrSet), but also supports iterators. If
+<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
+transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
more than 'N' insertions are performed, a single quadratically
probed hash table is allocated and grows as needed, providing extremely
efficient access (constant time insertion/deleting/queries with low constant
factors) and is very stingy with malloc traffic.</p>
-<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
+<p>Note that, unlike <tt>std::set</tt>, the iterators of <tt>SmallPtrSet</tt> are invalidated
whenever an insertion occurs. Also, the values visited by the iterators are not
visited in sorted order.</p>
@@ -1960,6 +1960,10 @@
errs() << *Inst << "\n";
}
</pre>
+Note that dereferencing a <tt>Value::use_iterator</tt is not a very cheap
+operation. Instead of performing <tt>*i</tt> above several times, consider
+doing it only once in the loop body and reusing its result.
+
</div>
<p>Alternatively, it's common to have an instance of the <a
@@ -1981,11 +1985,13 @@
</pre>
</div>
-<!--
- def-use chains ("finding all users of"): Value::use_begin/use_end
- use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
--->
-
+<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
+mutation free algorithms (such as analyses etc.). For this purpose above
+iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
+and <tt>Value::const_op_iterator</tt>. They automatically arise when
+calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
+<tt>const User*</tt>s respectively. Upon dereferencing, they return
+<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.
</div>
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