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:
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:
Permit use of the `mad', `madu' and `mul' instructions, as on the
> > 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.