[Bug tree-optimization/61346] New: VRP chooses bad bounds for variable

[ian at airs dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61346

            Bug ID: 61346
           Summary: VRP chooses bad bounds for variable
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ian at airs dot com
                CC: cmang at google dot com

The attached file, which is a Go test case converted to C code, should compile
and run without error.  It works with GCC 4.6.3 and GCC 4.9 branch with and
without optimization.  It works with mainline with -O0 and -O1.  It fails with
mainline with -O2.

I think the problem is in the VRP pass.  I see this in 067.vrp1:

i_3: [data$len_58, 9223372036854775806]  EQUIVALENCES: { i_65 } (1 elements)

This is flat out wrong, as inspection of 066.mergephi2 shows that the ideally
correct range of i_3 should be something like [0, data$len_58].  What's
particularly odd is that i_3 is even set to i_1, and the range of i_1 is
VARYING.