[PATCH][C/C++] Do not promote return arguments

[Andrew Haley]

Paolo Bonzini writes:
 > 
 > > I don't think it breaks any standard C/C++ code, but the ABI allows
 > > C/C++ code to be called from assembler (and other languages) and
 > > defines how return values should be promoted.  It's quite proper for
 > > assembly code to assume that return values are promoted according to
 > > their type, and this is where the libffi breakage came from.
 > > 
 > > Also, non-portable C/C++code that assumes that short and char values
 > > will be promoted to ints will be broken by this change.  Sure, it's
 > > nonstandard C/C++ code, but according to the ABI it shouldn't break.
 > > We don't know how much code of this kind there is.
 > 
 > I agree with Andrew, but OTOH I think that this is an i386 backend bug, 
 > previously masked by the C++ front-end.

That seems reasonable.  However, let's fix the back end first,
shouldn't we?

Andrew.