[Bug c/14319] incorrect optimization of union of structs with common initial sequences

["bangerth at dealii dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From bangerth at dealii dot org  2004-02-27 19:24 -------
Leaving aside questions of what the standard actually (is supposed to) mean: 
if the aliasing rules are changed as you propose, then 
- adding a union somewhere to a code will change the code generated for 
  the function in your example, even if this union is not actually used 
  anywhere 
- this takes away quite a number of opportunities for optimization, since 
  it is certainly not uncommon for code to use small structures that have, 
  say, an integer or pointer as first argument (think iterators and 
  accessors). 
 
In my eyes, both are not exactly positive consequences. But that's a personal 
opinion, not a language lawyer's statement. 
 
W. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14319