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Re: Bit-field patch, resurrected
- From: "Joseph S. Myers" <jsm at polyomino dot org dot uk>
- To: Richard Henderson <rth at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 2 Apr 2004 01:13:22 +0000 (UTC)
- Subject: Re: Bit-field patch, resurrected
- References: <Pine.LNX.4.58.0403162148050.24060@digraph.polyomino.org.uk><20040401225530.GF31591@redhat.com>
On Thu, 1 Apr 2004, Richard Henderson wrote:
> On Tue, Mar 16, 2004 at 09:50:14PM +0000, Joseph S. Myers wrote:
> > + /* For ENUMERAL_TYPEs, must check the mode of the types, not the precision;
> > + in C++ they have precision set to match their range, but may use a wider
> > mode to match an ABI. If we change modes, we may wind up with bad
> > + conversions. For INTEGER_TYPEs, must check the precision as well, so
> > + as to yield correct results for bit-field types. */
> > + mode_only_needed = (TREE_CODE (type) == ENUMERAL_TYPE);
>
> How does this interact with the enum bitfield extension?
It turned out that the enum bit-fields (of narrower width) could get the
special integer type rather than an enum type without causing problems for
debug info (unlike with the original patch; I don't know why).
> > +#define LANG_HOOKS_REDUCE_BIT_FIELD_OPERATIONS false
>
> Is this really the correct default? I guess it's the safe one for now,
> but I would expect that *any* language that sets TYPE_PRECISION small
> would want the semantics controlled by this flag.
C++ enum types get TYPE_PRECISION set artificially small. I don't know
that this means they want code generated to reduce widths. I didn't
investigate why Ada didn't like the other default.
--
Joseph S. Myers
jsm@polyomino.org.uk