Re: [RFC] Extend ipa-bitwise-cp with pointer alignment propagation

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Sep 21, 2016 at 6:44 PM, Prathamesh Kulkarni
<prathamesh.kulkarni@linaro.org> wrote:
> Hi,
> The attached patch tries to extend ipa bits propagation to handle
> pointer alignment propagation.
> The patch just disables ipa-cp-alignment pass, I suppose we want to
> eventually remove it ?
>
> Bootstrap+tested on x86_64-unknown-linux-gnu.
> Cross-tested on arm*-*-*, aarch64*-*-*.
> Does the patch look OK ?

Just looking at the alignment extraction:

+      else

if (POINTER_TYPE_P (...))

+       {
+         unsigned tem = bits[i].mask.to_uhwi ();
+         unsigned HOST_WIDE_INT bitpos = bits[i].value.to_uhwi ();
+         unsigned align = tem & -tem;
+         unsigned misalign = bitpos & (align - 1);
...
+             if (old_known
+                 && old_align > align)
+               {
+                 if (dump_file)
+                   fprintf (dump_file, "But alignment was already %u.\n",
old_align);
+                 continue;
+               }

it would be nice to sanity check old misalign against misalign.
Basically

   gcc_assert (misalign & (old_align - 1) == old_misalign)

here (and in the old_align > align case the reverse).

+             set_ptr_info_alignment (pi, align, misalign);


-         ret |= propagate_alignment_accross_jump_function (cs, jump_func,
-
&dest_plats->alignment);
+//       ret |= propagate_alignment_accross_jump_function (cs, jump_func,
+//

this should of course be removed rather than commented.

Leaving the IPA parts to somebody else.

Richard.


> Thanks,
> Prathamesh