Re: [patch] More thorough checking in reg_fits_class_p

[Richard Earnshaw <rearnsha at arm dot com>]

On 26/04/12 14:20, Jim MacArthur wrote:
> The current code in reg_fits_class_p appears to be incorrect; since 
> offset may be negative, it's necessary to check both ends of the range 
> otherwise an array overrun or underrun may occur when calling 
> in_hard_reg_set_p. in_hard_reg_set_p should also be checked for each 
> register in the range of regno .. regno+offset.
> 
> A negative offset can occur on a big-endian target. For example, on 
> AArch64, subreg_regno_offset (0, DImode, 0, TImode) returns -1.
> 
> We discovered this problem while developing unrelated code for 
> big-endian support in the AArch64 back end.
> 
> I've tested this with an x86 bootstrap which shows no errors, and with 
> our own AArch64 back end.
> 
> Ok for trunk?
> 
> gcc/Changelog entry:
> 
> 2012-04-26 Jim MacArthur<jim.macarthur@arm.com>
>       * recog.c (reg_fits_class_p): Check every register between regno and
>         regno+offset is in the hard register set.
> 

OK.

R.

> 
> reg-fits-class-9
> 
> 
> diff --git a/gcc/recog.c b/gcc/recog.c
> index 8fb96a0..825bfb1 100644
> --- a/gcc/recog.c
> +++ b/gcc/recog.c
> @@ -2759,14 +2759,28 @@ bool
>  reg_fits_class_p (const_rtx operand, reg_class_t cl, int offset,
>  		  enum machine_mode mode)
>  {
> -  int regno = REGNO (operand);
> +  unsigned int regno = REGNO (operand);
>  
>    if (cl == NO_REGS)
>      return false;
>  
> -  return (HARD_REGISTER_NUM_P (regno)
> -	  && in_hard_reg_set_p (reg_class_contents[(int) cl],
> -				mode, regno + offset));
> +  /* We should not assume all registers in the range regno to regno + offset are
> +     valid just because each end of the range is.  */
> +  if (HARD_REGISTER_NUM_P (regno) && HARD_REGISTER_NUM_P (regno + offset))
> +    {
> +      unsigned int i;
> +
> +      unsigned int start = MIN (regno, regno + offset);
> +      unsigned int end = MAX (regno, regno + offset);
> +      for (i = start; i <= end; i++)
> +	{
> +	  if (!in_hard_reg_set_p (reg_class_contents[(int) cl],
> +				  mode, i))
> +	    return false;
> +	}
> +      return true;
> +    }
> +  return false;
>  }
>  
>  /* Split single instruction.  Helper function for split_all_insns and