On Tue, Nov 05, 2013 at 01:23:00PM -0700, Jeff Law wrote:
> On 10/31/13 18:03, Cong Hou wrote:
> >(This patch is for the bug 58728:
> >http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58728)
> >
> >As in the bug report, consider the following loop:
> >
> >int foo(unsigned int n)
> >{
> > if (n != 0)
> > if (n != 1)
> > if (n != 2)
> > if (n != 3)
> > if (n != 4)
> > return ++n;
> > return n;
> >}
> >
> >The range test optimization should be able to merge all those five
> >conditions into one in reassoc pass, but I fails to do so. The reason
> >is that the phi arg of n is replaced by the constant it compares to in
> >case of == or != comparisons (in vrp pass). GCC checks there is no
> >side effect on n between any two neighboring conditions by examining
> >if they defined the same phi arg in the join node. But as the phi arg
> >is replace by a constant, the check fails.
I can't reproduce this, at least not on x86_64-linux with -O2,
the ifcombine pass already merges those.
Jakub
