[PATCH, GCC] PR middle-end/55299, fold bitnot through ASR and rotates

[Mikhail Maltsev]

On 05/11/2016 10:52 AM, Marc Glisse wrote:
> +/* ~((~X) >> Y) -> X >> Y (for arithmetic shift).  */
> +(simplify
> + (bit_not (convert? (rshift (bit_not @0) @1)))
> +  (if (!TYPE_UNSIGNED (TREE_TYPE (@0))
> +       && TYPE_PRECISION (type) <= TYPE_PRECISION (TREE_TYPE (@0)))
> +   (convert (rshift @0 @1))))
> 
> Is there a particular reason to split the converting / non-converting
> cases? For rotate, you managed to merge them nicely.
Fixed (i.e., merged two shift simplifications into one).
> 
> +
> +(simplify
> + (bit_not (convert? (rshift (convert@0 (bit_not @1)) @2)))
> +  (if (!TYPE_UNSIGNED (TREE_TYPE (@0))
> +       && TYPE_PRECISION (TREE_TYPE (@0)) <= TYPE_PRECISION (TREE_TYPE (@1))
> +       && TYPE_PRECISION (type) <= TYPE_PRECISION (TREE_TYPE (@0)))
> +   (with
> +    { tree shift_type = TREE_TYPE (@0); }
> +     (convert (rshift:shift_type (convert @1) @2)))))
> +
> +/* Same as above, but for rotates.  */
> +(for rotate (lrotate rrotate)
> + (simplify
> +  (bit_not (convert1?@0 (rotate (convert2?@1 (bit_not @2)) @3)))
> +   (if (TYPE_PRECISION (TREE_TYPE (@1)) <= TYPE_PRECISION (TREE_TYPE (@2))
> +        && TYPE_PRECISION (TREE_TYPE (@0)) <= TYPE_PRECISION (TREE_TYPE (@1)))
> +    (with
> +     { tree operand_type = TREE_TYPE (@2); }
> +      (convert (rotate:operand_type @2 @3))))))
> 
> Is that really safe when the conversion from @2 to @1 is narrowing? I
> would expect something closer to
> (convert (rotate (convert:type_of_1 @2) @3))
> so the rotation is done in a type of the same precision as the original.
> 
> Or
> (convert (rotate:type_of_1 (convert @2) @3))
> if you prefer specifying the type there (I don't), and note that you
> need the 'convert' inside or specifying the type on rotate doesn't work.
Fixed.

> 
> I have a slight preference for element_precision over TYPE_PRECISION (which for
> vectors is the number of elements), but I don't think it can currently cause
> issues for these particular transformations.
Fixed.
> 
> I don't know if we might want some :c / single_use restrictions, maybe on the
> outer convert and the rshift/rotate.
> 
I don't think :c can be used here. As for :s, I added it, as you suggested.

Also, I tried to add some more test cases for rotate with conversions, but
unfortunately GCC does not recognize rotate pattern, when narrowing conversions
are present.

-- 
Regards,
    Mikhail Maltsev
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fold_asr2_3.patch
Type: application/x-patch
Size: 4595 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20160513/326afaa1/attachment.bin>