RFA: hardware can have ISA attributes, too

[Doug Evans <dje@transmeta.com>]

Jim Blandy writes:
 > I don't really feel like I understand CGEN's data model well enough to
 > know whether this is really appropriate, or just a kludge.
 > 
 > Here's the motivation.  We have a toolchain that supports several
 > different machines within a family; some register sets are present on
 > some machines, but not on others.  Given an ISA, we want to be able to
 > traverse the hardware list and see which register sets are available
 > on that ISA.
 > 
 > So along with this will come another patch that produces an extern
 > declaration for @arch@_cgen_hw_table, so we can traverse it.
 > 
 > What's the best way to do this?

The patch to mach.scm is fine.

I'm not sure about the patch to provide extern @arch@_cgen_hw_table though.
If it's ultimately needed, great.
The way it's intended to normally work is that you access the CGEN_HW_ENTRY
elements via struct cgen_cpu_desc . hw_table.
struct cgen_cpu_desc is filled by the call to @arch@_cgen_cpu_open,
and the hw_table member is filled in based on the requested machs, not isas.
That's why, I think, I didn't initially add the extern declaration.
OTOH, if that were the case I would have made it static ...
And if it's not static, where's its entry in some header?

I don't know enough about the application at hand to know whether
all the hw entries you want to look at are in cgen_cpu_desc . hw_table,
but given that I didn't make the hw_table static, it should have
an extern declaration anyway.  Thus go for it.
[There are other tables in the same boat, but we can to them on
an as-needed basis.]