This is one of the patches I was talking about last week. The intent
is to let the target decide when attributes are "compatible", not just
whether the callee's attributes permit inlining in general (that hook
doesn't appear to be callee-context-specific any more, so you can't
cheat and check cfun).
The MeP port supports two types of modes; core and vliw. Vliw mode
packs one core insn and one coprocessor insn in a bundle, so the code
generator is the same but the intrinsics differ (there are extra copro
insns in vliw mode). Thus, every function is tagged (implicitly or
explicitly) as core or vliw, and you can only inline into same-mode
functions. Calls from a core function to a "static inline vliw" one
need to be blocked completely.