[Bug tree-optimization/80603] New: Optimize loads from constant arrays or aggregates with arrays

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80603

            Bug ID: 80603
           Summary: Optimize loads from constant arrays or aggregates with
                    arrays
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

Created attachment 41301
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41301&action=edit
gcc8-cst-load.patch

The vrp113.c testcase (a copy of vrp40.c) is now XFAILed, because the switch
optimization does a better job on it, but we don't manage to figure out that no
matter what the index is we load always the same constant.
For integer loads, we can also figure ranges from those even if the constants
aren't the same, similarly for pointers (always NULL vs. always non-NULL vs.
anything).