On Tue, Feb 17, 2015 at 11:26 AM, Ajit Kumar Agarwal
<ajit.kumar.agar...@xilinx.com> wrote:
>
>
> -----Original Message-----
> From: Richard Biener [mailto:richard.guent...@gmail.com]
> Sent: Tuesday, February 17, 2015 3:42 PM
> To: Ajit Kumar Agarwal
> Cc: gcc@gcc.gnu.org; Vinod Kathail; Shail Aditya Gupta; Vidhumouli Hunsigida;
> Nagaraju Mekala
> Subject: Re: Tree SSA If-combine optimization pass in GCC
>
> On Tue, Feb 17, 2015 at 9:22 AM, Ajit Kumar Agarwal
> <ajit.kumar.agar...@xilinx.com> wrote:
>> Hello All:
>>
>> I can see the IF-combining (If-merging) pass of optimization on tree-ssa
>> form of intermediate representation.
>> The IF-combine or merging takes of merging the IF-THEN-ELSE if the
>> condition Expr found be congruent or Similar.
>>
>> The IF-combine happens if the two IF-THEN-ELSE are contiguous to each other.
>> If the IF-THEN-ELSE happens to be not contiguous but are wide apart with
>> there is code in between.
>> Does the If-combine takes care of this. This requires to do the
>> head-duplication and Tail-duplication for the Code in between If-THEN-ELSE
>> to bring the IF-THEN-ELSE contiguous to each other.
>>
>> After the head and tail duplication of the code in between the
>> IF-THEN-ElSE sequence becomes contiguous to each other. Apart from
>> this, Does the tree-ssa-if-combine pass considers the control flow of the
>> body of the IF-THEN-ELSE. Is there any limitation on control flow of the
>> body of the IF-THEN-ELSE.
>>
>> Can I know the scope of tree-ssa-ifcombine optimizations pass with respect
>> to the above points.
>>
>> Thoughts Please?
>
>>>if-combine is a simple CFG + condition pattern matcher. It does not perform
>>>head/tail duplication. Also there is no "control flow" in the bodies,
>>>control flow is part of the CFG that is >>matched so I'm not quite getting
>>>your last question.
>
> Thanks ! My last question was If there is a control flow likes loops inside
> the IF-THEN-ELSE, which could be possible if the Loop unswitching is performed
> and the Loop body is placed inside the IF-THEN-ELSE, then in that case the
> two IF-THEN-ELSE can be merged if the cond expr matches and the control flow
> of the body of If-then-else matches?
>
> There are many cases in SPEC 2006 benchmarks where the IF-combine could be
> enabled if the if-then-else sequence is made contiguous by performing
> the head/tail duplication.
I'd be curious what those cases look like. Care to file some bugreports
with testcases?
>>>if-combine was designed to accompany IL-only patterns that get partly
>>>translated into control flow. Like
>
> >>tem1 = name & bit1;
> >>tem2 = name & bit2;
> >>tem3 = tem1 | tem2;
> >>if (tem3)
> ...
>
>>>vs.
>
> >>tem1 = name & bit1;
> >>if (tem1)
> >>goto x;
> >>else
> >>{
> >>tem2 = name & bit2;
> >>if (tem2)
> >> goto x;
> >>}
>
>>>x:
> >>...
> Thanks for the examples. This explains the scope of if-combine optimization
> pass.
>
> Thanks & Regards
> Ajit
>
> Richard.
>
>> Thanks & Regards
>> Ajit
