[Bug tree-optimization/64822] New: tree-ssa-sccvn miscompile union containing bitfield for big-endian targets

[jiwang at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64822

            Bug ID: 64822
           Summary: tree-ssa-sccvn miscompile union containing bitfield
                    for big-endian targets
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jiwang at gcc dot gnu.org

given the following simple testcase,

union {
  unsigned f0;
  unsigned f1 : 24;
} const g_3983 = {1};

int main() {
  printf("checksum = %08x\n", g_3983.f1);
}

on aarch64, or other target support big-endian, then 

./cc1 -O2 -mbig-endian test.c

during tree-ssa-sccvn pass g_3983.f1 is evaluated into constant 1 while I think
it should be zero for big-endian.