On Fri, Apr 27, 2012 at 12:42:41PM +0800, Thomas Schwinge wrote:
> > > GET_MODE_BITSIZE (lmode)« (8 bits). (With the current sources, lmode is
> > > VOIDmode.)
> > >
> > > Is emmitting »BIT_FIELD_REF <*common, 32, 0> & 255« wrong in this case,
> > > or should a later optimization pass be able to figure out that
> > > »BIT_FIELD_REF <*common, 32, 0> & 255« is in fact the same as
> > > common->code, and then be able to conflate these? Any suggestions
> > > where/how to tackle this?
> >
> > The BIT_FIELD_REF is somewhat of a red-herring. It is created by
> > fold-const.c
> > in optimize_bit_field_compare, code that I think should be removed
> > completely.
> > Or it needs to be made aware of strict-volatile bitfield and C++ memory
> > model
> > details.
I'd actually very much prefer the latter, just disable
optimize_bit_field_compare for strict-volatile bitfield mode and when
avoiding load data races in C++ memory model (that isn't going to be
default, right?). This optimization is useful, and it is solely about
loads, so even C++ memory model usually shouldn't care.
Jakub
