Need clarification for PPC floating Point compiler options

[Rohit Arul Raj]

Hello All,

I have a few clarification with the PPC floating point compiler options.
I am working with v4.4.1 (e500mc) but i think it applies to 4.6 as well.

1. -msingle-float:

 With this option, i get a compiler warning: "-msingle-float option
equivalent to -mhard-float" which means both the single-float and
double-float flags should be set.
 But in the back-end file config/rs6000/rs6000.c,  rs6000_double_float
is set to 0.

    case OPT_msingle_float:
         if (!TARGET_SINGLE_FPU)
          warning (0, "-msingle-float option equivalent to -mhard-float");
         /* -msingle-float implies -mno-double-float and TARGET_HARD_FLOAT. */
        rs6000_double_float = 0;
        target_flags &= ~MASK_SOFT_FLOAT;
        target_flags_explicit |= MASK_SOFT_FLOAT;
      break;

  Still the FP code gets generated for both float and double. Do we
have any other target flag/macro which overrides 'rs6000_double_float'
flag?

2. -mfpu=none

  I expected this option to behave like '-msoft-float', but it works
like '-mhard-float'.
  The comments and internal flags in the target source file also
mention the same.

  case OPT_mfpu_:
      if (fpu_type != FPU_NONE)
      /* If -mfpu is not none, then turn off SOFT_FLOAT, turn on HARD_FLOAT. */
      {
         ...
      }
      else
      {
        /* -mfpu=none is equivalent to -msoft-float */
        target_flags |= MASK_SOFT_FLOAT;
        target_flags_explicit |= MASK_SOFT_FLOAT;
        rs6000_single_float = rs6000_double_float = 0;
        }

3. powerpc-linux-gcc --help gives the following text for -mfpu:

          -mfpu=                      Specify FP (sp, dp, sp-lite,
dp-lite) (implies -mxilinx-fpu)

         There seems to be a typo here as the supported options are:
"none", "sp_lite", "dp_lite", "sp_full", "dp_full"

          static enum fpu_type_t
         rs6000_parse_fpu_option (const char *option)
         {
             if (!strcmp("none", option)) return FPU_NONE;
             if (!strcmp("sp_lite", option)) return FPU_SF_LITE;
             if (!strcmp("dp_lite", option)) return FPU_DF_LITE;
             if (!strcmp("sp_full", option)) return FPU_SF_FULL;
             if (!strcmp("dp_full", option)) return FPU_DF_FULL;

4.  What is the purpose of this option? "-mfloat-gprs="

     when passed "yes/single/double", they generate instructions like
"efsmul" for a simple float multiplication statement which belong to
SPE engine.
     Since e500mc doesn't support SPE instruction set and if
"-mfloat-gprs=" enables them then should this option throw an
warning/error?

Regards,
Rohit