"Georg-Johann Lay" <a...@gjlay.de> writes:
>> This patch takes a different approach to fixing PR52543 than does the
>> patch in
>>
>> http://gcc.gnu.org/ml/gcc-patches/2012-03/msg00641.html
>>
>> This patch transforms the lower-subreg pass(es) from unconditionally
>> splitting wide moves, zero extensions, and shifts, so that it now takes
>> into account the target specific costs and only does the transformations
>> if it is profitable.
>
> As far as I understand the pass, it's not only about splitting these
> instructions
> but also to the additional benefits of the split, i.e. AND 0xfffffffe will
> only need
> one QI operation instead of 1 SI operation that costs 4 QI.
>
> And in fact, the positive benefit of subreg-lowering occurs with bit-wise
> operations
> like AND, IOR, EOR etc.
Hmm, but in that case, why define andsi3 at all? optabs applies exactly
that decomposition if you don't:
/* These can be done a word at a time. */
if ((binoptab == and_optab || binoptab == ior_optab || binoptab == xor_optab)
&& mclass == MODE_INT
&& GET_MODE_SIZE (mode) > UNITS_PER_WORD
&& optab_handler (binoptab, word_mode) != CODE_FOR_nothing)
Richard
