Hi,
As discussed in PR90078, this patch checks possible infinite_cost overflow in ivopts.
Also as discussed, overflow happens mostly because of cost scaling wrto bb_freq/loop_freq.
For the moment, we only implement capping in comp_cost operators, while in next
stage1, we may instead implement capping in get_scaled_computation_cost_at with
more supporting benchmark data.

BTW, I think switching costs around comparison between infinite_cost is unnecessary
since there will be no overflow in integer after capping with infinite_cost.

Bootstrap and test on x86_64, is it OK?

Thanks,
bin

2019-04-17  Bin Cheng  <bin.cheng@linux.alibaba.com>

        PR tree-optimization/92078
        * tree-ssa-loop-ivopts.c (comp_cost::operator +,-,+=,-+,/=,*=): Add
        checks for infinite_cost overflow.

2018-04-17  Bin Cheng  <bin.cheng@linux.alibaba.com>

        PR tree-optimization/92078
        * gcc/testsuite/g++.dg/tree-ssa/pr90078.C: New test.