[Libre-soc-isa] [Bug 1087] change pseudocode to prevent output register write only when causing a fp trap and output is in same regfile as input

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Wed May 24 02:30:29 BST 2023


--- Comment #20 from Jacob Lifshay <programmerjake at gmail.com> ---
other *fun* side-effects of fcvtfg not writing RT (if we decide to not accept
my proposal) is that we either have to manually calculate CR0 in the pseudocode
or not change CR0 (messes with data-dependent fail-first) or (probably the
worst option) read RT and calculate CR0 from the read-in value. (CR1 doesn't
have that problem since it's input always comes from FPSCR).

I think the best option is to just have fcvtfg always write RT as I proposed,
since suppressing writes (so the trap handler can see the input) is only
necessary when targeting the same register file as inputs.

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