Re: [PATCH v2] Store_bit_field_1: Use SUBREG instead of REG if possible

[Eric Botcazou <botcazou@adacore.com>]

> I don't see that.  That's definitely not what GCC expects here,
> the left-most word of the doubleword should be unchanged.
> 
> Your testcase should be a dg-do-run and probably more like
> 
> NOMIPS16 int __attribute__((noipa)) test (const unsigned char *buf)
> {
>   int val;
>   ((unsigned char*)&val)[0] = *buf++;
>   ((unsigned char*)&val)[1] = *buf++;
>   ((unsigned char*)&val)[2] = *buf++;
>   ((unsigned char*)&val)[3] = *buf++;
>   return val;
> }
> int main()
> {
>   int val = 0x01020304;
>   val = test (&val);
>   if (val != 0x01020304)
>     abort ();
> }
> 
> not sure if I got endianess correct.  Now, the question is what
> WORD_REGISTER_OPERATIONS implies for a bitfield insert and what
> the MIPS ABI says for returning SImode.

WORD_REGISTER_OPERATIONS must *not* be taken account for bit-fields, see e;g. 
word_register_operation_p:

/* Return true if X is an operation that always operates on the full
   registers for WORD_REGISTER_OPERATIONS architectures.  */

inline bool
word_register_operation_p (const_rtx x)
{
  switch (GET_CODE (x))
    {
    case CONST_INT:
    case ROTATE:
    case ROTATERT:
    case SIGN_EXTRACT:
    case ZERO_EXTRACT:
      return false;
    
    default:
      return true;
    }
}

-- 
Eric Botcazou