Am 31.07.2014 15:32, schrieb Johannes Pfau:
Am Wed, 30 Jul 2014 17:32:10 -0700
schrieb Andrei Alexandrescu <[email protected]>:
On 7/30/14, 5:29 PM, Andrei Alexandrescu wrote:
On 7/30/14, 4:51 PM, Tobias Müller wrote:
With relatively 'dumb' compilers, this is not a big problem, but
optimizers
are more and more clever and will take profit of such assumptions
if they can.
That's true, and it seems like a growing trend. Relevant threads:
https://groups.google.com/a/isocpp.org/forum/#!topic/std-proposals/9S5jNRW-5wY
http://www.spinics.net/lists/gcchelp/msg41714.html
Recent versions of gcc and clang have become increasingly aggressive
about optimizing code by taking advantage of making undefined
behavior _really_ undefined. There's been a couple of posts in the
news recently that I can't find at the moment.
I think I found it: http://www.redfelineninja.org.uk/daniel/?p=307
Andreu
Also this:
Linus Torvalds On GCC 4.9: Pure & Utter Crap
http://www.phoronix.com/scan.php?page=news_item&px=MTc1MDQ
(This actually is a GCC bug, but valid behaviour for normal C++ code.
GCC only broke the compiler switch to explicitly force non-standard
behaviour)
And don't forget this (rather old) case:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8537
(I really don't get why anyone would want such an optimization: I want
an optimizer to use clever inlining, use SSE etc where it makes sense
and stuff like that - but not to remove code I wrote.)
Cheers,
Daniel
