On 2021-06-21 20:36, Richard Biener wrote:
On Mon, 21 Jun 2021, guojiufu wrote:
On 2021-06-21 14:19, guojiufu via Gcc-patches wrote:
> On 2021-06-09 19:18, guojiufu wrote:
>> On 2021-06-09 17:42, guojiufu via Gcc-patches wrote:
>>> On 2021-06-08 18:13, Richard Biener wrote:
>>>> On Fri, 4 Jun 2021, Jiufu Guo wrote:
>>>>
>>> cut...
> cut...
>>
Besides the method in the previous mails,
I’m thinking of another way to split loops:
foo (int *a, int *b, unsigned k, unsigned n)
{
while (++k != n)
a[k] = b[k] + 1;
}
We may split it into:
if (k<n)
{
while (++k < n) //loop1
a[k] = b[k] + 1;
}
else
{
while (++k != n) //loop2
a[k] = b[k] + 1;
}
In most cases, loop1 would be hit, the overhead of this method is only
checking “if (k<n)”
which would be smaller than the previous method.
That would be your original approach of versioning the loop. I think
I suggested that for this scalar evolution and dataref analysis should
be enhanced to build up conditions under which IV evolutions are
affine (non-wrapping) and the versioning code in actual transforms
should then do the appropriate versioning (like the vectorizer already
does for niter analysis ->assumptions for example).
Hi Richi,
Thanks for your suggestion!
The original idea was trying to cover cases like multi-exit loops, while
it
seems not benefited too much. The method you said would help for common
cases.
I'm thinking of the methods to implement this:
During scev analyzing, add more possible wrap checking (especially for
unsigned)
for convert_affine_scev/scev_probably_wraps_p/chrec_convert_1;
introducing
no_wrap_assumption for the conditions of no-wrapping on given chrec/iv.
And using this assumption in simple_iv_with_niters/dr_analyze_innermost.
One question is, where is the best place to add this assumption?
Is it a flexible idea to add no_wrap_assumption to affine_iv/loop, and
set the assumption when scev checks wrap?
Thanks for your suggestions!
BR.
Jiufu
Richard.
cut....
