Hi Arturas, On Tuesday 03 May 2005 17:36, Arturas Moskvinas wrote: > > Simple question, but I'm not entirely clear from reading the > > documentation > > > > If I have a gcc configured for i686-* target system and I use that > > compiler to build a package without any -m submodel options , is the > > generated code 1) only suitable for i686 and better, or > > 2) tuned for i686 and better but still OK for i386 > > From gcc manual: > While picking a specific cpu-type will schedule things appropriately > for that particular chip, the compiler will not generate any code that > does not run on the i386 without the -march=cpu-type option being > used. Yes, I have read that, but it does _not_ answer my question, which is concerned with the default behaviour of a compiler configured and built for a specific sub-model target. :) > It means even if you make -march=pentium-4 and run this code on 386 it > will run (maybe you'll have problems with SSE (but i think gcc inserts > code to bypass sse if you do not have it)). No - you are wrong here. If you use -mpcu or mtune, it will run on i386, but if you use -march, it most certainly will not. > > > What about 32bit code generated with x86_64 targeted gcc (with -m32)? > > From the same gcc manual: Yes, I have read this but it still doesn't answer my question ;) This, from Ian Lance Taylor on the main gcc ML, answers my question: > Andrew Walrond <andrew@xxxxxxxxxxx> writes: > > If I have a gcc configured for i686-* target system and I use that > > compiler to build a package without any -m submodel options , is the > > generated code 1) only suitable for i686 and better, or > > 2) tuned for i686 and better but still OK for i386 > > The latter. Configuring for i686-* is equivalent to configuring for > i386-* with the option --with-cpu=i686. This causes the compiler to > be built as though you specified -mtune=i686 for each compile which > does not explicitly use -mtune, -march, or -mcpu. > > > Whatever the answer, is it a generic rule that holds true for submodels > > of all architectures? > > It should always be true, although of course there may be bugs. > > > What about 32bit code generated with x86_64 targeted gcc (with -m32)? > > If you configure for x86-64, I believe the default architecture will > be MMX, SSE, and SSE2. I believe that will apply even if you use > -m32. But I haven't really tested it. > > Ian Thanks for the reply though. I admit Ian had to read between the lines to understand exactly what I was getting at :) Andrew Walrond
