[Bug optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

["mycroft at netbsd dot org" <gcc-bugzilla at gcc dot gnu dot org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792



------- Additional Comments From mycroft at netbsd dot org  2003-10-28 20:52 -------
Created an attachment (id=5014)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=5014&action=view)
proposed fix

The problem is thus:

* The {u,}mulsidi3 generate two parallel sets which modify the upper and lower
halves of the target register.

* life_analysis() does not track subregister modifications -- if you don't
modify the whole register with a single set, it considers the register
unused.

The simple, if klugy, solution to this is to stick an explicit clobber in.  It
seems to work.

While doing this, I noticed that constant folding was not happening for
32x32->64 multiplies.  This is because the parallel set generated by
{u,}mulsidi3 cannot be folded at all.  To solve this, I first expand to a
normal multiply, and then use a define_insn_and_split to convert it to the
parallel set after CSE and constant folding.