On Fri, Mar 13, 2009 at 2:14 PM, Bernd Schmidt <bernds_...@t-online.de> wrote: > Paolo Bonzini wrote: >> These are all the !SHIFT_COUNT_TRUNCATED targets. >> >> For 4.5 I would like to improve our RTL canonicalization so that no >> out-of-range shifts are ever in the RTL representation. >> >> This in turn means that the description given by SHIFT_COUNT_TRUNCATED >> must be exact. Right now !SHIFT_COUNT_TRUNCATED means "I don't know", >> I want it to mean "it is never truncated". >> >> I would like to know whether for avr,bfin,cris,frv,h8300,pdp11,rs6000 >> (which define SHIFT_COUNT_TRUNCATED as 0) and for mcore,sh,vax (which >> do not define it at all) it is right that shift counts are never >> truncated. > > The Blackfin does not truncate shift counts. The documentation > specifies that e.g. for "Dx >>= Dy" instructions, shift counts greater > than 31 produce a result of zero. Other shift instructions use a sign > extended part of the shift count to shift either left or right. "I > don't know" is probably the best answer we can give the compiler.
Hm. In fold-const.c we try to make sure to produce the same result as the target would for constant-folding shifts. Thus, Paolo, I think what fold-const.c does is what we should assume for !SHIFT_COUNT_TRUNCATED. No? Richard.
