[Bug target/64204] New: gcc.dg/c11-atomic-2.c fails on powerpc 64-bit little endian after -mupper-regs patches went in

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64204

            Bug ID: 64204
           Summary: gcc.dg/c11-atomic-2.c fails on powerpc 64-bit little
                    endian after -mupper-regs patches went in
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: meissner at gcc dot gnu.org
              Host: powerpc64le-unknown-linux-gnu
            Target: powerpc64le-unknown-linux-gnu
             Build: powerpc64le-unknown-linux-gnu

The test gcc.dg/c11-atomic-2.c fails on powerpc 64-bit little endian when it is
compiled without optimization and the target compiler was configured with
--with-cpu=power8.  If you optimize the code, it works, and if you compile it
with the -mno-upper-regs-df option.

The core problem is that an old optimization for Darwin which converts loading
up TFmode constants at RTL generation breaks when DFmode registers can go in
Altivec registers.

While looking at the code, I noticed that we weren't optimizing setting the
TFmode to 0.0L on VSX systems, and added support for that as well.