PBLENDVB is weird. My guess is that it wasn't an execution or rename limit, since PBLENDVB should be "just as hard", but a decode or (pre-rename) uop format li

PBLENDVB is weird. My guess is that it wasn't an execution or rename limit, since PBLENDVB should be "just as hard", but a decode or (pre-rename) uop format limit: i.e., the uop format in the IDQ couldn't handle three variable inputs, but the implicit xmm0 is fine (doesn't take any space). Or the decoders couldn't handle it. Still, once 3-input stuff like FMA did appear I don't know why it wasn't fixed. Possibly FMA has special handling...