On Dec 31, 2006, at 19:13, Daniel Berlin wrote:
> Note the distinct drop in performance across almost all the benchmarks
> on Dec 30, including popular programs like bzip2 and gzip.
Not so.
To my eyes, the specint 2000 mean went UP by about 1% for the
base -O3 compilation. The peak enabled more unrolling, which
is helped by additional range information provided by absence
of -frwapv.
So, I'd say this run would suggest enabling -fwrapv for
at least -O1 and -O2. Also, note that we never have
focussed on performance with -fwrapv, and it is quite
likely there is quite some improvement possible.
I'd really like using -fwrapv by default for -O, -O[s12].
The benefit of many programs moving from "undefined semantics"
to "implementation-defined semantics, overflow wraps like in
old compilers" far outweighs even an average performance loss
of 2% as seen in specfp.