On 1/1/07, Geert Bosch <[EMAIL PROTECTED]> wrote:
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.
I would support the proposal to enable -fwrapv for -O[01], but not for -O2 as that is supposed to be "optimize for speed" and as -O3 is not widely used to optimize for speed (in fact it may make code slower). I'm undecided for -Os but care less about it. Richard.
