From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Lipe To: Mark Mitchell Cc: gcc@gcc.gnu.org Subject: Re: type based aliasing again Date: Sun, 12 Sep 1999 08:16:00 -0000 Message-id: <19990912101059.C21534@rjlhome.sco.com> References: <9909120057.AA36240@marc.watson.ibm.com> <19990911182424A.mitchell@codesourcery.com> X-SW-Source: 1999-09/msg00463.html Mark Mitchell wrote: > >>>>> "David" == David Edelsohn writes: > > David> FYI, IBM's AIX compiler does not enable "ANSI > David> aliasing" by default when the compiler is invoked with > > Someone reported something similar for the DEC copmiler; `cc' is > -fno-strict-aliasing, while some more progressive-sounding compiler > name is -fstrict-aliasing. > > One thing important about these data points, though, is that major > vendors must be finding that not too many programs use the invalid > constructs in question. Otherwise, they would not have dared to > enable these options. (Of course, they could have the kind of The SCO UnixWare (and therefore, UDK) compilers for IA32 do perform this at high levels of optimization. The Intel C Compiler performs this optimization, but only if you explictly add the '-distype' flag. I can't recall having been bitten by either (I uses the UW compiler much more than icc) but I don't really know how aggressively either optimizes this specific construct. OTOH, the UW compiler frequently generates better code than GCC so I'm inclined to say if there's an optimization opportunity it probably grabs it. RJL From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Lipe To: Mark Mitchell Cc: gcc@gcc.gnu.org Subject: Re: type based aliasing again Date: Thu, 30 Sep 1999 18:02:00 -0000 Message-ID: <19990912101059.C21534@rjlhome.sco.com> References: <9909120057.AA36240@marc.watson.ibm.com> <19990911182424A.mitchell@codesourcery.com> X-SW-Source: 1999-09n/msg00463.html Message-ID: <19990930180200.9K-eKq_fPnEAxNvtpH_-iobnq03URR4cA0Ssk6Jq2Ns@z> Mark Mitchell wrote: > >>>>> "David" == David Edelsohn writes: > > David> FYI, IBM's AIX compiler does not enable "ANSI > David> aliasing" by default when the compiler is invoked with > > Someone reported something similar for the DEC copmiler; `cc' is > -fno-strict-aliasing, while some more progressive-sounding compiler > name is -fstrict-aliasing. > > One thing important about these data points, though, is that major > vendors must be finding that not too many programs use the invalid > constructs in question. Otherwise, they would not have dared to > enable these options. (Of course, they could have the kind of The SCO UnixWare (and therefore, UDK) compilers for IA32 do perform this at high levels of optimization. The Intel C Compiler performs this optimization, but only if you explictly add the '-distype' flag. I can't recall having been bitten by either (I uses the UW compiler much more than icc) but I don't really know how aggressively either optimizes this specific construct. OTOH, the UW compiler frequently generates better code than GCC so I'm inclined to say if there's an optimization opportunity it probably grabs it. RJL