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Re: RFC/RFA: patch for PR 22156: improve SRA for bit-fields
> Would you please let me know whether this is still the case for the
> patch I've just posted in the thread "Reload bug & SRA oddness"?
> http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00317.html
Well, you can just build the Ada compiler (it builds now) on your preferred
platform and run it on the testcase at -O. There should be no BIT_FIELD_REF
at all after SRA.
> I'm not sure why this is bad, if the bitfield access patterns are
> whole-word accesses, which presumably access a single register.
If this reasoning was true, then why not simply replace all COMPONENT_REFs
with BIT_FIELD_REFs?
> I see that that register allocation may be poorer because of the pairing.
But SRA is supposed to *split* structures, not split and reassemble them in a
more convoluted way!
> I wonder if clipping align at BITS_PER_WORD is the right answer... It
> would limit coalescing of wider bit-fields, but this is probably not
> such a big deal.
I'd simply test DECL_BIT_FIELD.
--
Eric Botcazou