[Bug middle-end/79673] New: GIMPLE verification fails when compiling code with __seg_gs

[me at manueljacob dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79673

            Bug ID: 79673
           Summary: GIMPLE verification fails when compiling code with
                    __seg_gs
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: me at manueljacob dot de
                CC: jakub at gcc dot gnu.org, rguenther at suse dot de
  Target Milestone: ---

Created attachment 40814
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40814&action=edit
Compiler traceback

This happens at least on x86-64 with -O2 and higher.  If I pass code like this,

void used(double x);
void usel(long x);
void test(int c) {
    if (c) {
        used(*((double __seg_gs *) 0));
    } else {
        usel(*((long __seg_gs *) 0));
    }
}

the compiler ICEs (using some GCC-slang I learned from the comments to my
previous bug report ;)) in verify_gimple (full traceback attached).

It seems like the problematic IR is created in SSA PRE, although my GCC
debugging skills are too limited to verify this (I couldn't manage to print the
IR before and after this particular pass).