[Libre-soc-bugs] [Bug 230] Video opcode development and discussion

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Sat May 29 07:07:03 BST 2021


--- Comment #71 from cand at gmx.com ---
So in starting the mp3 SV code, I hit one of ppc's obvious lacks: it has no
move GPR to/from FPR instrs. This means that zeroing a FPR requires a memory
load, and that zero takes memory space too.

I think they did that because loading immediates sucks for them. That is not a
concern for us, I believe we (will) have efficient immediate loading, no? In
that case, I propose we add mtf/mff. A standalone "zero FPR" instr would work
too, but more flexibility is better.

Modern POWER with altivec uses the vector xor instruction for that, since the
FPR space is shared with the vector register space. They have no "move GPR
to/from VR" either.

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