Hello, On Thu, 18 Apr 2019 14:42:22 +0200 Richard Biener <richard.guent...@gmail.com> wrote:
> On Thu, Apr 18, 2019 at 2:20 PM Uecker, Martin > <martin.uec...@med.uni-goettingen.de> wrote: > > 1.) Compilers do not use conditional equivalences for > > optimizations of pointers (or only when additional > > conditions apply which make it safe) > > > > 2.) We make pointer comparison between a pointer > > and a one-after pointer of a different object > > undefined behaviour. > > Yes please! No please don't, not UB. If any of this, make the result unspecified but not UB, please. > OTOH GCC transforms > (uintptr_t)&a != (uintptr_t)(&b+1) > into &a != &b + 1 (for equality compares) and then > doesn't follow this C rule anyways. Actually our proposal we are discussing here goes exactly the other way around. It basically reduces &a != &b + 1 to (uintptr_t)&a != (uintptr_t)(&b+1) with only an exception for null pointers, but which probably don't matter for a platform where null pointers are just all bits 0. Jens -- :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt ::
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