Re: casting return values

[Jim Wilson <wilson at specifixinc dot com>]

Dan Nicolaescu wrote:
> Currently return values for C/C++ functions that return types for
> which c_promoting_integer_type_p is true are cast to integer 
> (see c-decl.c:start_function and cp/decl.c:start_function)

This came up in another thread recently, though I don't recall which 
one.  I looked at this code, and noticed that it has been there since at 
least gcc-1.42.  I didn't bother looking back any further.  I think this 
is some left over K&R C code.  I don't know of any reason why gcc needs 
to be promoting return values here.  I suspect the right fix is to just 
delete it.

However, there is the concern that removing this may accidentally break 
some targets, because it will effectively be an ABI change.  Targets 
that do need return values promoted should be defining 
TARGET_PROMOTE_FUNCTION_RETURN and PROMOTE_FUNCTION_MODE.  However, 
there are likely some targets that require the promotion but do not 
currently define these macros.

Maybe there is already enough breakage in gcc-3.5 because of the 
tree-ssa merge that we can justify the risk of one more?

I don't see the need for any langhook.  A langhook is used when the 
middle end needs different behaviour for different languages, but if the 
C languages requires promotion for function return values, then it is 
likely part of the ABI, and will have to apply to all languages.  Thus 
the existing TARGET_PROMOTE_FUNCTION_RETURN should be OK.
--
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com