Re: [wide-int] Remove SHIFT_COUNT_TRUNCATED uses at tree/gimple level

[Richard Sandiford <rdsandiford at googlemail dot com>]

Kenneth Zadeck <zadeck@naturalbridge.com> writes:
> So what is the big plan here?     if you remove it here and then do not 
> do it in wide int, then it is not going to be truncated.

Yeah, that is the big plan for trees.  Mainline doesn't truncate at the
tree level after:

    http://gcc.gnu.org/ml/gcc-patches/2013-11/msg00285.html

and this patch brings wide-int back in line.  (The truncations in this patch
were only ever local to wide-int.)

If you're wondering why we don't want to truncate at the tree level,
see the second half of:

    http://gcc.gnu.org/ml/gcc-patches/2013-11/msg00174.html

Thanks,
Richard

> On 11/06/2013 05:10 PM, Richard Sandiford wrote:
>> Following the removal of SHIFT_COUNT_TRUNCATED from double-int, this patch
>> reverts the changed I'd made to mimic the old behaviour on wide-int.
>>
>> Tested on powerpc64-linux-gnu and by assembly comparison on a range of targets.
>> OK to install?
>>
>> Thanks,
>> Richard
>>
>>
>> Index: gcc/fold-const.c
>> ===================================================================
>> --- gcc/fold-const.c	2013-11-05 13:06:56.985255941 +0000
>> +++ gcc/fold-const.c	2013-11-05 13:12:28.805655903 +0000
>> @@ -1007,13 +1007,9 @@ int_const_binop_1 (enum tree_code code,
>>   	/* It's unclear from the C standard whether shifts can overflow.
>>   	   The following code ignores overflow; perhaps a C standard
>>   	   interpretation ruling is needed.  */
>> -	res = wi::rshift (arg1, arg2, sign,
>> -			  SHIFT_COUNT_TRUNCATED
>> -			  ? GET_MODE_BITSIZE (TYPE_MODE (type)) : 0);
>> +	res = wi::rshift (arg1, arg2, sign);
>>         else
>> -	res = wi::lshift (arg1, arg2,
>> -			  SHIFT_COUNT_TRUNCATED
>> -			  ? GET_MODE_BITSIZE (TYPE_MODE (type)) : 0);
>> +	res = wi::lshift (arg1, arg2);
>>         break;
>>         
>>       case RROTATE_EXPR:
>> Index: gcc/tree-ssa-ccp.c
>> ===================================================================
>> --- gcc/tree-ssa-ccp.c	2013-11-05 13:07:25.659474362 +0000
>> +++ gcc/tree-ssa-ccp.c	2013-11-05 13:12:28.806655910 +0000
>> @@ -1272,20 +1272,15 @@ bit_value_binop_1 (enum tree_code code,
>>   		  else
>>   		    code = RSHIFT_EXPR;
>>   		}
>> -	      int shift_precision = SHIFT_COUNT_TRUNCATED ? width : 0;
>>   	      if (code == RSHIFT_EXPR)
>>   		{
>> -		  *mask = wi::rshift (wi::ext (r1mask, width, sgn),
>> -				      shift, sgn, shift_precision);
>> -		  *val = wi::rshift (wi::ext (r1val, width, sgn),
>> -				     shift, sgn, shift_precision);
>> +		  *mask = wi::rshift (wi::ext (r1mask, width, sgn), shift, sgn);
>> +		  *val = wi::rshift (wi::ext (r1val, width, sgn), shift, sgn);
>>   		}
>>   	      else
>>   		{
>> -		  *mask = wi::ext (wi::lshift (r1mask, shift, shift_precision),
>> -				   width, sgn);
>> -		  *val = wi::ext (wi::lshift (r1val, shift, shift_precision),
>> -				  width, sgn);
>> +		  *mask = wi::ext (wi::lshift (r1mask, shift), width, sgn);
>> +		  *val = wi::ext (wi::lshift (r1val, shift), width, sgn);
>>   		}
>>   	    }
>>   	}