Re: [PATCH 2/3]Improve induction variable elimination

["Bin.Cheng" <amker.cheng@gmail.com>]

On Fri, Jul 25, 2014 at 8:35 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Thu, Jul 17, 2014 at 11:08 AM, Bin Cheng <bin.cheng@arm.com> wrote:
>> Hi,
>> As quoted from the function difference_cannot_overflow_p,
>>
>>   /* TODO: deeper inspection may be necessary to prove the equality.  */
>>   switch (code)
>>     {
>>     case PLUS_EXPR:
>>       return expr_equal_p (e1, offset) || expr_equal_p (e2, offset);
>>     case POINTER_PLUS_EXPR:
>>       return expr_equal_p (e2, offset);
>>
>>     default:
>>       return false;
>>     }
>>
>> The overflow check can be improved by using deeper inspection to prove the
>> equality.  This patch deals with that by making below two improvements:
>>   a) Handles constant cases.
>>   b) Uses affine expansion as deeper inspection to check the equality.
>>
>> As a result, functions strip_wrap_conserving_type_conversions and
>> expr_equal_p can be removed now.  A test case is also added to illustrate iv
>> elimination opportunity captured by this patch.
>>
>> Thanks,
>> bin
>
> You add special casing for constants but I don't see any testcases for that.
> Specifically
>
> +  /* No overflow if offset is zero.  */
> +  if (offset == integer_zero_node)
>      return true;
>
> is a bogus check (use integer_zerop).  Apart from the special-casing of
> constants the patch looks good to me.

Hi Richard,
I modified the patch according to your comments by removing the
constant case.  Re-bootstrap and test on x86_64 and x86.  Is this
version OK?

Thanks,
bin

2014-08-06  Bin Cheng  <bin.cheng@arm.com>

    * tree-ssa-loop-ivopts.c (ivopts_data): New field name_expansion.
    (tree_ssa_iv_optimize_init): Initialize name_expansion.
    (tree_ssa_iv_optimize_finalize): Free name_expansion.
    (strip_wrap_conserving_type_conversions, expr_equal_p): Delete.
    (difference_cannot_overflow_p): New parameter.  Use affine
    expansion for equality check.
    (iv_elimination_compare_lt): Pass new argument.

gcc/testsuite/ChangeLog
2014-08-06  Bin Cheng  <bin.cheng@arm.com>

    * gcc.dg/tree-ssa/ivopts-lt-2.c: New test.