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(MIPS R5900) Adding support for the FPU (COP1) instructions


Hi all,

Thank you all for the help so far. This is probably the final part of my efforts to complete support for the R5900 within GCC, but I need help this time because the existing homebrew GCC version has no support for this (despite what its README file says). Hence I have nothing to refer to.

The R5900 has support for a couple of floating-point arithmetic, with its FPU (COP1). The FPU instructions are something like these:
MADD.S (rd <- ACC + rs * rt)
MADDA.S (ACC <- ACC + rs * rt)
MSUB.S  (rd <- ACC - rs * rt)
MSUBA.S (ACC <- ACC - rs * rt)
ADDA.S (ACC <- rs + rt)
SUBA.S (ACC <- rs - rt)
MULA.S (ACC <- rs * rt)

These instructions are similar to those floating-point instructions with similar-looking names, in normal MIPS processors. But they involve the R5900's FPU accumulator (ACC) register instead.
I didn't find an explicit instruction to move values to/from the ACC register.


I've added instruction patterns (or added new alternatives to existing patterns) to the pattern file for the R5900, but I have not seen GCC emit any of these new instructions. I did add a new register (the ACC register), as well as a matching constraint and predicate.

Is there a proper way for me to debug this? Or is this not working, simply because GCC can't support such instructions on its own (it looks complicated to issue)?

Thanks and regards,
-W Y


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