Re: middle-end/9725: Invalid dependency determination

["Jan Beulich" <JBeulich@novell.com>]

The following reply was made to PR middle-end/9725; it has been noted by GNATS.

From: "Jan Beulich" <JBeulich@novell.com>
To: <bangerth@ticam.utexas.edu>
Cc: <velco@fadata.bg>,<gcc-bugs@gcc.gnu.org>, <gcc-gnats@gcc.gnu.org>
Subject: Re: middle-end/9725: Invalid dependency determination
Date: Wed, 19 Feb 2003 18:08:42 +0100

 But why is the structure incompatible?
 
 "... an aggregate or union type that includes one of the aforementioned
 types among its
 members (including, recursively, a member of a subaggregate or
 contained union), ..."
 
 The structure does include two fields of type 'unsigned' (the fact that
 they are bit fields doesn't alter their type as I view it). And, as
 already asked, when the second store is deemed non-conflicting, then why
 isn't the first store, too? And, with respect to the other mail - short
 of not using this logic - how do I access sub-fields of a built-in type
 (while the code I have to fix for others to overcome the optimizer
 problem uses ints, I'm really more interested in accessing sub-fields of
 floating point types (other than through memcpy-ing the float into and
 afterwards out of a structure)?
 
 Thanks, Jan
 
 >>> Wolfgang Bangerth <bangerth@ticam.utexas.edu> 19.02.03 17:59:46
 >>>
 
 > struct s {
 > 	unsigned f1:16;
 > 	unsigned f2:16;
 > };
 > 
 > void test(unsigned *pf, unsigned x, unsigned y) {
 > 	unsigned f;
 > 
 > 	((struct s*)&f)->f1 = x;
 > 	((struct s*)&f)->f2 = y;
 > 	*pf = f;
 > }
 
 You still try to access the bits of the unsigned int variable f through
 
 the bits of the incompatible structure s. Short answer: don't do that.
 
 W.
 
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 Wolfgang Bangerth             email:           
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