[Bug tree-optimization/71707] [7 Regression] ICE in get_stridx_plus_constant

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71707

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 38799
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38799&action=edit
gcc7-pr71707.patch

Untested fix.