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Re: IVOPT improvement patch


There is a problem in this patch -- when i wraps to zero and terminate
the loop, the maxoffset computed will be zero which is wrong.

My previous patch won't have this problem.

David

On Fri, Jul 30, 2010 at 9:49 AM, Xinliang David Li <davidxl@google.com> wrote:
> This looks fine to me -- Zdenek or other reviewers --- is this one ok?
>
> Thanks,
>
> David
>
> On Fri, Jul 30, 2010 at 8:45 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Thu, Jul 29, 2010 at 6:04 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> It looks strange:
>>>
>>> + ? ? ?width = (GET_MODE_BITSIZE (address_mode) < ?HOST_BITS_PER_WIDE_INT - 1)
>>> + ? ? ? ? ?? GET_MODE_BITSIZE (address_mode) : HOST_BITS_PER_WIDE_INT - 1;
>>> ? ? ? addr = gen_rtx_fmt_ee (PLUS, address_mode, reg1, NULL_RTX);
>>> - ? ? ?for (i = start; i <= 1 << 20; i <<= 1)
>>> + ? ? ?for (i = 1; i < width; i++)
>>> ? ? ? ?{
>>> - ? ? ? ? XEXP (addr, 1) = gen_int_mode (i, address_mode);
>>> + ? ? ? ? ?HOST_WIDE_INT offset = (1ll << i);
>>> + ? ? ? ? XEXP (addr, 1) = gen_int_mode (offset, address_mode);
>>> ? ? ? ? ?if (!memory_address_addr_space_p (mem_mode, addr, as))
>>> ? ? ? ? ? ?break;
>>> ? ? ? ?}
>>>
>>> HOST_WIDE_INT may be long or long long. "1ll" isn't always correct.
>>> I think width can be >= 31. Depending on HOST_WIDE_INT,
>>>
>>> HOST_WIDE_INT offset = -(1ll << i);
>>>
>>> may have different values. The whole function looks odd to me.
>>>
>>>
>>
>> Here is a different approach to check address overflow.
>>
>>
>> --
>> H.J.
>> --
>> 2010-07-29 ?H.J. Lu ?<hongjiu.lu@intel.com>
>>
>> ? ? ? ?PR bootstrap/45119
>> ? ? ? ?* tree-ssa-loop-ivopts.c (get_address_cost): Re-apply revision
>> ? ? ? ?162652. ?Check address overflow.
>>
>


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