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

[jameskuyper at verizon dot net]

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

James Kuyper Jr. <jameskuyper at verizon dot net> changed:

           What    |Removed                     |Added
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                 CC|                            |jameskuyper at verizon dot net

--- Comment #11 from James Kuyper Jr. <jameskuyper at verizon dot net> ---
(In reply to Tim Rentsch from comment #10)
...
> Four:  Despite the last observation, the "one special guarantee" clause
> (and hence also DR 257) is clearly not germane to this problem.  The
> reason for this is that the "one special guarantee" clause is concerned
> with read access ("inspect" is the word used in the Standard), but the
> example code has no read accesses, only write accesses.  That paragraph
> of the Standard is not relevant here.

The example code includes the statement
    return xp->x;

Which does in fact inspect (read) the value currently stored in a variable that
is part of the common initial sequence. The fact that if fails to read the
value most recently written to that location is the defect that's being
reported.