Re: r4600 flag

[Ralf Baechle <ralf@oss.sgi.com>]

On Tue, Jul 31, 2001 at 10:06:35AM +0200, Kevin D. Kissell wrote:

> Using mips-linux-gcc from egcs-2.91.66, I don't see exactly this
> behavior in the test case above.  I *do* see that *if* I have -mcpu=4600
> set *and* I have not otherwise set the ISA level to be MIPS I or
> MIPS II (-mips1, -mips2), 64-bit instructions will be emitted.
> But that's to be expected.

No, it contradict the GCC documentation:

`-mcpu=CPU TYPE'
     Assume the defaults for the machine type CPU TYPE when scheduling
     instructions.  The choices for CPU TYPE are `r2000', `r3000',
     `r3900', `r4000', `r4100', `r4300', `r4400', `r4600', `r4650',
     `r5000', `r6000', `r8000', and `orion'.  Additionally, the
     `r2000', `r3000', `r4000', `r5000', and `r6000' can be abbreviated
     as `r2k' (or `r2K'), `r3k', etc.  While picking a specific CPU
     TYPE will schedule things appropriately for that particular chip,
     the compiler will not generate any code that does not meet level 1
     of the MIPS ISA (instruction set architecture) without a `-mipsX'
     or `-mabi' switch being used.

> To generate 32-bit code for an
> R4600-like platform, you need to specify both the ISA level
> (to deal with issues like the above) and the R4600 pipeline
> (to get the MAD instruction).

No MAD on R4600.  Again it would be in contradiction with above document-
ation.  Mad you get with:

`-mmad'
`-mno-mad'
     Permit use of the `mad', `madu' and `mul' instructions, as on the
     `r4650' chip.

> > Is there a truly correct -mcpu option for a mips32 cpu?
> 
> It's "-mips32", which is sort of a -mips option and a -mcpu
> option rolled into one.  It's supported by several gnu distributions,
> notably those of Algorithmics and Cygnus/Red Hat.  I believe
> that someone at MIPS or Algorithmics succeeded in building
> a Linux kernel of some description using the Algorithmics
> SDE, but I don't know the details.

  Ralf