On Wed, Jan 12, 2011 at 8:27 AM, Ian Lance Taylor <i...@google.com> wrote: > Gidi Nave <gidi.nav...@gmail.com> writes: > >> On Tue, Jan 11, 2011 at 7:22 PM, Ian Lance Taylor <i...@google.com> wrote: >>> Gidi Nave <gidi.nav...@gmail.com> writes: >>> >>>> On Tue, Jan 11, 2011 at 5:34 PM, Ian Lance Taylor <i...@google.com> wrote: >>>> >>>>> So why doesn't d1 = d1 + -96 match the last instruction there? >>>>> >>>> because it's: add d,d unsigned >>>> we don't have: add d,d signed >>>> >>>> and in this case we need: d = r + (-96) >>> >>> Addition of signed and unsigned numbers is the same operation at the >>> machine level. Are there limitations on the signed value? If so, is >>> there is a sub instruction? >> >> There are limitation for the signed value for D class registers. >> There is a sub instruction for D registers, but it's limited to U5 >> (unsigned of 5 bits) which is not the case here. > > Thanks. Since we don't know the details of your processor, we could be > more helpful if you provided this sort of information up front. It > sounds like you are saying that there is no way to subtract 96 without > using an extra register. Is that correct? > > If that is the case, then I agree with Jeff that you are going to need > to define a secondary reload. Look at TARGET_SECONDARY_RELOAD in the > docs. > > By the way, if the restrictions on addition (which you did not describe) > are less severe than the restrictions on subtraction, then you should > consider adjusting your frame pointer so that most stack slots are at a > positive offset rather than a negative one. I don't know if that is > what is going on here, though a negative offset is certainly unusual. > > Ian >
Hi Ian, There is no way to subtract 96 without the extra register. The secondary reload worked great !!! Thanks! Regarding the frame pointer - in my case it was the frame pointer but our addition/subtract instructions options are similar (for the same register classes), so adjusting the frame pointer won't do any good. One more question: GCC usually knows how to handle cases which need decomposition of expressions due to architecture limitations. In my case it didn't know. How can I foreseen additional such cases, in order to avoid compilation crush? Thanks, Gidi.
