[Bug tree-optimization/42587] New: bswap not recognized for union

["andi-gcc at firstfloor dot org" <gcc-bugzilla@gcc.gnu.org>]

From
http://embed.cs.utah.edu/embarrassing/dec_09/harvest/gcc-head_llvm-gcc-head/

typedef unsigned char u8;
typedef unsigned int u32;
#pragma pack(1)
#pragma pack()
#pragma pack(1)
#pragma pack()
#pragma pack(1)
#pragma pack()
#pragma pack(4)
#pragma pack()
union __anonunion_out_195
{
  u32 value;
  u8 bytes[4];
};
union __anonunion_in_196
{
  u32 value;
  u8 bytes[4];
};
extern void acpi_ut_track_stack_ptr (void);
u32 acpi_ut_dword_byte_swap (u32 value);
u32
acpi_ut_dword_byte_swap (u32 value)
{
  union __anonunion_out_195 out;
  union __anonunion_in_196 in;

  {
    acpi_ut_track_stack_ptr ();
    in.value = value;
    out.bytes[0] = in.bytes[3];
    out.bytes[1] = in.bytes[2];
    out.bytes[2] = in.bytes[1];
    out.bytes[3] = in.bytes[0];
    return (out.value);
  }
}

/* Checksum = 1251E213 */


does not turn into bswap, while llvm does that.

There's bswap detection code in tree-ssa-math-ops.c, but it doesn't
seem to work for this union pattern. Perhaps it should?


-- 
           Summary: bswap not recognized for union
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andi-gcc at firstfloor dot org
  GCC host triplet: x86_64-linux
GCC target triplet: x86_64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42587