[Bug middle-end/29274] [4.2/4.3/4.4 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2009-03-27 17:26 -------
The issue is that TER does not build large trees for the multiplications as
the factors are used multiple times (and come from memory).  Thus the expander
does not see the widened multiplication and appearantly combine / lower-subreg
is not able to optimize this.

I think with expand-from-SSA we could enable this optimization during expand.

Simplified testcase:

long long foo (int i, int j)
{
   return (long long)i * (long long)j * (long long)i;
}

because we CSE (long long)i we don't optimize this case.  Disabling tree-level
CSE re-enables the optimizations: -fno-tree-fre -fno-tree-pre 
-fno-tree-dominator-opts


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|target                      |middle-end
 GCC target triplet|arm-unkown-elf              |arm-unkown-elf, i?86-*-*
           Keywords|                            |missed-optimization
            Summary|4.1, 4.2 (possibly 4.0?) not|[4.2/4.3/4.4 Regression] not
                   |using mulsidi3              |using mulsidi3
   Target Milestone|---                         |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274