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[Bug libstdc++/51965] Redundant move constructions in heap algorithms
- From: "chris at bubblescope dot net" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 23 Jan 2012 14:04:43 +0000
- Subject: [Bug libstdc++/51965] Redundant move constructions in heap algorithms
- Auto-submitted: auto-generated
- References: <bug-51965-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51965
Chris Jefferson <chris at bubblescope dot net> changed:
What |Removed |Added
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CC| |chris at bubblescope dot
| |net
--- Comment #2 from Chris Jefferson <chris at bubblescope dot net> 2012-01-23 14:04:43 UTC ---
>From my memory of originally writing this, from the old non-moving version,
these moves were originally copies.
The reason I believe those moves are there is because in some cases the
original location is written over. For example trace the behaviour of push_heap
/ __push_heap.
I'm not saying your patch is wrong, and I can't currently compile a g++ svn
head to check, but have you run the tester with your patch, and have you
checked the logic carefully to make sure you can't scribble over the value in
the algorithm?
There may will still be a way of reducing the work to just one move of course,
at the start of the algorithm.
Sorry if you have already considered this, but I remember bits of this being
subtle.