[Bug target/84711] New: AArch32 big-endian fails when taking subreg of a vector mode to a scalar mode.

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84711

            Bug ID: 84711
           Summary: AArch32 big-endian fails when taking subreg of a
                    vector mode to a scalar mode.
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: tnfchris at gcc dot gnu.org
          Reporter: tnfchris at gcc dot gnu.org
  Target Milestone: ---
            Target: armeb-*-*

The following example

typedef __fp16 v4f16
  __attribute__ ((vector_size (8)));

v4f16 fn1 (v4f16 p)
{
  return p;
}

fails only on arm big-endian when using `-mfpu=neon -mfloat-abi=hard
-mfp16-format=ieee -mbig-endian` and results in an ICE.

This case triggers an endless recursion in the mid-end when taking the subreg
and eventually segfaults when it runs out of stack space.