-----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.
>>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
