> On Sep 13, 2018, at 10:39 AM, Andrew Stubbs <a...@codesourcery.com> wrote:
>
> On 13/09/18 15:16, Paul Koning wrote:
>> If you don't have machine operations that add without messing with
>> condition codes, wouldn't it make sense to omit the definition of the
>> add-pointer patterns? GCC will build things out of normal
>> (CC-clobbering) adds if there are no add-pointer operations, which
>> may well be more efficient in most cases than explicitly
>> saving/restoring a CC that may in fact not matter right at that
>> spot.
>
> I thought the whole point of addptr is that it *is* needed when add
> clobbers CC? As in, LRA spills are malformed without this.
>
> Did something change? The internals manual still says "It only needs to
> be defined if addm3 sets the condition code."
It's ambiguous, because the last sentence of that paragraph says "addm3 is used
if addptrm3 is not defined."
I don't know of any change in this area. All I know is that pdp11 has adds
that clobber CC and it doesn't define addptrm3, relying on that last sentence.
I've tried LRA and for the most part it compiles successfully, I suppose I
should verify the generated code based on the point you raised. If I really
have to define addptr, I'm in trouble because save/restore CC is not easy on
pdp11.
paul
