🚀 go-pugleaf

can@cam-orl.co.uk (Cosmos Nicolaou) writes:

>is it really the case that gcc will generate code for pre-sparc-v8 (e.g.
>lx/sparc 10) cpu's by default and that the only way to enable the use of
>the v8's hardware mul/div instructions is via explicit use of the mv8
>flag?? 

Yes.  The same is true for the Sun C compiler as well.  Currently,
only the MicroSPARC I & II and the SuperSPARC[+] have v8 instructions.

The main reason for not using those instructions by default is the
fact that programs compiled with -v8 (-xcg92) run much slower on
pre-v8 SPARCs.  In Solaris 2.3 only the sun4d kernel is compiled
with SPARC v8 instructions.

>Do similar comments apply to machines with an fpu? (e.g. lx)

All Sun SPARCs have been shipped with FPUs (except for some very
early 4/1xx).  In Solaris 2.x, those early CPUs have been disabled
and the FPU instructions are emulated in the kernel.

The early FPUs are so broken that code generated for them needs
all kinds of costly work arounds.  Instead, Sun has chosen to
generate code that runs (much) faster on all new CPUs, and disable
the FPU on the broken systems (4/1xx and 4/2xx).

Casper