On Mon, Sep 14, 2020 at 08:35:44PM +0100, Richard Sandiford wrote: > Segher Boessenkool <seg...@kernel.crashing.org> writes: > >> Although this looks/sounds complicated, the advantage is that everything > >> remains up-to-date. If we instead added a second attribute and only > >> defined it for instructions like *add_<shift>_<mode>, other instructions > >> (including config/arm instructions) would still have type alu_shift_imm > >> but would have a shift_imm_value of "none". > > > > I would make an attribute for the mode (or data size really), and one > > that says the insn uses shifted data (since many arm insns have that, > > just like record form on PowerPC is everywhere). And you can have that > > one filled "by magic" usually! > > I don't think this is really answering my point above though. > What I meant is: we currently have several instructions in config/arm > and config/aarch64 that have type alu_shift_imm. If we add some new > on-the-side attributes A, but only update *some* of the alu_shift_imm > instructions to define A (either directly or indirectly), then the other > alu_shift_imm instructions will have the default values for A. > This probably isn't the intended effect. Ideally, every alu_shift_imm > instruction would specify correct attribute values for A (specifically, > to indicate whether the shift value is in [1, 4] or not). > > In contrast, one advantage of replacing the existing alu_shift_imm type > with two new types is that any existing reference to the old type will > cause a build failure. So keeping everything in a single type > attributes gives us static type checking that the information for each > (former) alu_shift_imm instruction is complete. Similarly for any other > type that needs to be split in the same way.
Removing the old types causes build failures as well if you forget some cases. > I realise this won't convince you, and I'm not trying to. :-) And you don't have to :-) I am telling you about a scheme that worked really well for us; I am not trying to convince you to do that in your own target, that decision is all your own. Segher
