[tree-ssa] More CCP fixes [patch]

[Neil Booth]

Fergus Henderson wrote:-

> On 12-Aug-2002, Mark Mitchell <mark@codesourcery.com> wrote:
> 
> That sounds reasonable to me so long as you are talking about the C++
> front-end.  For the language-independent form of trees, IMHO bit-fields
> should be treated as a distinct type.  C++ can represent them how it
> likes during parsing, semantic analysis, etc., but IMHO the C++ front-end
> should have to introduce the new types before passing the trees off to
> the language-independent parts of the compiler.
> 
> The idea of treating bit-fields as having the same type as something
> with a different set of values and a different sized representation
> is IMHO an ugly hack.  The C89 standard wasn't clear about whether bit-fields
> constituted a distinct type, but it has been clarified in defect reports
> and fixed in C99.  Unfortunately C++98 has perpetuated the mistake.
> But this nasty C/C++-ism should IMHO not be incorporated into GCC's
> language-independent interface.

Has it been reported as a C++ defect, too, then?  Or is C++ branching
at this point?

IMO the open PRs assigned to me related to bitfields, 6 or 7 of them,
show why having different types is a good idea.  GCC better understands
the range of non-overflow values, and gets sign promotion correct.
Having the same type makes promotion and various other things work
incorrectly, because of assumptions scattered around various parts
of GCC.

Neil.