Use __restrict for __relocate_object_a

[Marc Glisse]

Hello,

this small patch feels safe: we are moving an existing object to an 
uninitialized location so the 2 locations can't overlap. And it helps with 
std::vector<std::unique_ptr<int>> where it lets the compiler get rid of 
the branches "if(...) delete ..." when moving elements around, for 
instance in reserve(). We don't get a call to memmove yet (ldist may be 
confused by clobbers, I'll investigate and report that later), but the 
code gets much smaller at -O2, and we vectorize at -O3.

Similarly, I think the call to memmove in __relocate_a_1 could probably be 
memcpy (I don't remember why I chose memmove), but that seems less 
important and I don't want to mix it with this patch.

Bootstrap+regtest on x86_64-pc-linux-gnu.

2019-04-29  Marc Glisse  <marc.glisse@inria.fr>

 	PR libstdc++/87106
 	* include/bits/stl_uninitialized.h (__relocate_object_a): Mark the
 	arguments with __restrict.

-- 
Marc Glisse
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