Ian Lance Taylor <ian@airs.com> writes: > This kind of error generally means that the operand predicate accepts > an operand which no constraint matches. If the predicate (e.g., > register_operand) accepts an operand, then there must be a constraint > that matches it. Otherwise you will get an error in > constrain_operands, such as the above.
and later: > When I said this: > >> > This kind of error generally means that the operand predicate accepts >> > an operand which no constraint matches. If the predicate (e.g., >> > register_operand) accepts an operand, then there must be a constraint >> > that matches it. Otherwise you will get an error in >> > constrain_operands, such as the above. > > I mean that, in the instruction above, any operand which matches > nonimmediate_operand must be matched by at least one of the > constraints 'm' or 'r', and any operand which matches const0_operand > must match the constraint 'n'. This might confuse people. It sounds your first quote is saying that everything accepted by a predicate must also match at least one constraint, and of course that isn't true. E.g. register_operand accepts registers from any class, whereas 'r' only matches GENERAL_REGS. And it's usually OK (but not good practice, because it generates poor code) for a nonimmediate_operand to only provide 'r' constraints. More realistically, it's OK for a nonimmediate_operand to only allow memory constraints for some combinations of operands. It's reload's job to fix this sort thing. I realise I'm not telling you (Ian) anything new here, I just thought it was worth clarifying. Richard
