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| author | Gabor Greif <ggreif@gmail.com> | 2010-03-26 19:30:47 +0000 |
|---|---|---|
| committer | Gabor Greif <ggreif@gmail.com> | 2010-03-26 19:30:47 +0000 |
| commit | 4de7368bf92897d3b943423934e0a95d5a99d2cd (patch) | |
| tree | 324347357dcad827e6dc3b715450ea8b3ad92336 /docs/ProgrammersManual.html | |
| parent | 4d12d3b70fe91e80852f9867acef327dbfaf77d6 (diff) | |
add a blurb on const versions of chain traversals and a word of caution
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99638 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/ProgrammersManual.html')
| -rw-r--r-- | docs/ProgrammersManual.html | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/docs/ProgrammersManual.html b/docs/ProgrammersManual.html index cf936d1571..b6c9a8793c 100644 --- a/docs/ProgrammersManual.html +++ b/docs/ProgrammersManual.html @@ -1211,14 +1211,14 @@ and erasing, but does not support iteration.</p> <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 @@ for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i 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 @@ for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) </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> <!--_______________________________________________________________________--> |