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[Bug middle-end/60814] incorrect integer promotion when multiplying unsigned short values
- From: "pinskia at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 11 Apr 2014 00:15:50 +0000
- Subject: [Bug middle-end/60814] incorrect integer promotion when multiplying unsigned short values
- Auto-submitted: auto-generated
- References: <bug-60814-4 at http dot gcc dot gnu dot org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60814
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is undefined code as 0xffff*0xffff overflows int.
x * y is really
((int)x) * ((int)y)
So if that overflows and since we know that both (int)x and (int)y are both
positive integer since we are converting from unsigned short to int; the result
of ((int)x) * ((int)y) will also be positive (since overflow of signed integer
is undefined) we can remove the cast between int and unsigned int and go
directly to unsigned long long in a valid way.