[Bug libgcc/77813] New: __TMC_END__ - __TMC_LIST__ == 0

["glisse at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77813

            Bug ID: 77813
           Summary: __TMC_END__ - __TMC_LIST__ == 0
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
  Target Milestone: ---
            Target: powerpc64le-unknown-linux-gnu

In crtstuff.c, function deregister_tm_clones contains this code:

  if (__TMC_END__ - __TMC_LIST__ == 0)

this currently gives, in the original dump

  if (((unsigned long) &__TMC_END__ + 7) - (unsigned long) &__TMC_LIST__ <= 14)

I was testing an optimization that allows us to get instead

  if ((long int) &__TMC_END__ == (long int) &__TMC_LIST__)

During forwprop, the match.pd pattern (cmp (convert1?@2 addr@0) (convert2?
addr@1)) applies and we fold this to 0. In the libitm testsuite, most runtime
tests then segfault.

It seems that either the optimization to compare addresses is too eager, or the
code in crtstuff.c doesn't mark the variables appropriately...