[Bug c/85974] New: Failure to optimize difference of two pointers into a compile time constant

[pkoning at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85974

            Bug ID: 85974
           Summary: Failure to optimize difference of two pointers into a
                    compile time constant
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pkoning at gcc dot gnu.org
  Target Milestone: ---

This issue is exposed by test case testsuite/gcc.c-torture/compile/930326-1.c,
on platforms where ptrdiff_t is not "long" (such as pdp11).  In that case, the
last line:
   long i = s.f-&s.b;
fails with "error: initializer element is not computable at load time".

It's not a target bug; the problem can be reproduced for other targets by
changing the "long" to "char" in that statement.