Re: Identifying Chain of Recurrence

[Pritam Gharat <pritam01gharat at gmail dot com>]

I am writing a Simple IPA Pass which is inserted after ipa-pta. This
pass identifies whether a chain of recurrence is built by gcc or not.
I have used tree_is_chrec(t) to check if t represents chain of
recurrence and function find_var_scev_info(bb, var)  to obtain the
scev information generated (which comprises of chrec information).
However, find_var_scev_info() is a static function and cannot be
called from my plugin.

Is there any alternative way to get the chain of recurrence
information? Or do we need to change the gcc source code by making the
function find_var_scev_info() non-static and recompiling the source
code?

Thanks,
Pritam Gharat

On Fri, May 29, 2015 at 10:34 AM, Bin.Cheng <amker.cheng@gmail.com> wrote:
> On Fri, May 29, 2015 at 12:41 PM, Pritam Gharat
> <pritam01gharat@gmail.com> wrote:
>> GCC builds a chain of recurrence to capture a pattern in which an
>> array is accessed in a loop. Is there any function which identifies
>> that gcc has built a chain of recurrence? Is this information
>> associated to the gimple assignment which accesses the array elements?
>>
> GCC analyzes evolution of scalar variables on SSA representation.
> Each ssa var is treated as unique and can be analyzed.  If the address
> expression itself is a ssa var, it can be analyzed by scev; otherwise,
> the users of scev have to compute by themselves on the bases of other
> scev vars.  For example, address of MEM[scev_var] can be analyzed by
> scev; while address of MEM[invariant_base+scev_iv] is computed by
> users.  Well, at least this is how IVOPT works.  You can refer to
> top-file comment in tree-scalar-evolution.c for detailed information.
> General routines for chain of recurrence is in file tree-chrec.c.
>
> Thanks,
> bin
>>
>> Thanks,
>> Pritam Gharat