On Mon, 26 Dec 2005, Andrew Lenharth wrote:
I'm not sure I follow. If this is fixed by the architecture (seems
unlikely for alpha but...) you should be able to do something like this:
(set R27, (fooop GPRC:$in1, GPRC:$in2))
This works? That is about what I need.
Yes, assuming foo-op is an operation with one result, this will emit the
logical equivalent of:
(set GPRC:$tmp, (fooop GPRC:$in1, GPRC:$in2))
(copytoreg R27, $tmp)
... and flag them together.
it it is not fixed by the ISA, but fixed by the architecture, you should
handle this in the lowering code, and emit copyto/from regs.
The problem is that because they are jumps and calls, the results of the
operation must be in certain registers (and is visible in the called code).
The dest reg is not fixed in the instruction, but in the calling conventions.
Yeah, I figured... it's not like alpha to hard code that stuff in :)
Thus (Rd = BSR ...) has a calling convention specified reg for Rd, which is
not specified in the architecture. The hack is to fix it in the instruction
used and issue a copyfromreg.
I'd suggest handling this in the lower code then.
the closest I can get without that hack is (copyfromreg (copytoreg
(bsr ...))), but that cannot be emitted as
t = bsr
Rd = t
it must be
Rd = bsr
This requirement doesn't seem to be specified because I cannot specify the
output regs for an instruction.
In practice, this will always be copy coallesced away. I agree though
that this feels hacky and shouldn't be done.
I must encode the calling convention in the instruction descriptions.
If I wanted any other calling convention than linux alpha (which is the
same as Digital UNIX), I would have to have clones of those
instructions. Probably not something worth worrying about because of
the alpha, but I could see it affecting other archs.
Yup, for alpha, coming back around to where we started, I guess it
currently DOES make sense to encode the return reg into the instruction...
-Chris
--
http://nondot.org/sabre/
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