expansion of vector shifts...

Richard Biener richard.guenther@gmail.com
Wed Feb 13 11:15:00 GMT 2013


On Tue, Feb 12, 2013 at 11:31 PM, David Miller <davem@davemloft.net> wrote:
> From: David Miller <davem@redhat.com>
> Date: Fri, 16 Nov 2012 00:33:05 -0500 (EST)
>
>> From: Richard Sandiford <rdsandiford@googlemail.com>
>> Date: Mon, 29 Oct 2012 10:14:53 +0000
>>
>>> ...given that the code is like you say written:
>>>
>>>   if (SHIFT_COUNT_TRUNCATED)
>>>     {
>>>       if (CONST_INT_P (op1)
>>>         ...
>>>       else if (GET_CODE (op1) == SUBREG
>>>             && subreg_lowpart_p (op1)
>>>             && INTEGRAL_MODE_P (GET_MODE (SUBREG_REG (op1))))
>>>      op1 = SUBREG_REG (op1);
>>>     }
>>>
>>> INTEGRAL_MODE_P (GET_MODE (op1)) might be better than an explicit
>>> VECTOR_MODE_P check.  The code really doesn't make sense for anything
>>> other than integers.
>>>
>>> (It amounts to the same thing in practice, of course...)
>>
>> Agreed, I've just committed the following.  Thanks!
>>
>> ====================
>> Fix gcc.c-torture/compile/pr53410-2.c on sparc.
>>
>>       * expmed.c (expand_shift_1): Don't strip non-integral SUBREGs.
>
> This is broken on sparc again, although I'm confused about how this
> has happened.
>
> The suggestion was to use INTEGRAL_MODE_P as the test, so what's there
> in expand_shift_1() is:
>
>       else if (GET_CODE (op1) == SUBREG
>                && subreg_lowpart_p (op1)
>                && INTEGRAL_MODE_P (GET_MODE (SUBREG_REG (op1)))
>                && INTEGRAL_MODE_P (GET_MODE (op1)))
>         op1 = SUBREG_REG (op1);
>
> but INTEGRAL_MODE_P accepts vectors.  This is really confusing because
> I was absolutely sure I re-ran the test case with the fix I committed
> and it didn't crash any more.
>
> Maybe what we really mean to do here is check both op1 and SUBREG_REG
> (op1) against SCALAR_INT_MODE_P instead of INTEGRAL_MODE_P?

Yes.

> Something like this:
>
> gcc/
>
> 2013-02-12  David S. Miller  <davem@davemloft.net>
>
>         * expmed.c (expand_shift_1): Only strip scalar integer subregs.
>
> diff --git a/gcc/expmed.c b/gcc/expmed.c
> index 4a6ddb0..954a360 100644
> --- a/gcc/expmed.c
> +++ b/gcc/expmed.c
> @@ -2116,8 +2116,8 @@ expand_shift_1 (enum tree_code code, enum machine_mode mode, rtx shifted,
>                        % GET_MODE_BITSIZE (mode));
>        else if (GET_CODE (op1) == SUBREG
>                && subreg_lowpart_p (op1)
> -              && INTEGRAL_MODE_P (GET_MODE (SUBREG_REG (op1)))
> -              && INTEGRAL_MODE_P (GET_MODE (op1)))
> +              && SCALAR_INT_MODE_P (GET_MODE (SUBREG_REG (op1)))
> +              && SCALAR_INT_MODE_P (GET_MODE (op1)))
>         op1 = SUBREG_REG (op1);
>      }
>
>
>



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