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Date: Thu, 08 Oct 2009 16:23:00 -0000
From: Zdenek Dvorak <rakdver@kam.mff.cuni.cz>
To: Jean Christophe Beyler <jean.christophe.beyler@gmail.com>
Cc: gcc@gcc.gnu.org
Subject: Re: Turning off unrolling to certain loops
Message-ID: <20091008161802.GA30141@kam.mff.cuni.cz>
References: <c568a2600910051346n7ea55296iba879c4cae9f6be3@mail.gmail.com> <20091006065352.GB15626@kam.mff.cuni.cz> <c568a2600910060634v4d78ad75x463d7e20edeea0f4@mail.gmail.com> <20091006135624.GA18714@kam.mff.cuni.cz> <c568a2600910060756m96adf86mb1507c6717fdfdb6@mail.gmail.com> <20091006150918.GA19277@kam.mff.cuni.cz> <c568a2600910060828l24ec5ecct926eb2624a1d2157@mail.gmail.com> <c568a2600910080722k794552fvbde46fed95601b21@mail.gmail.com>
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Hi,

> 2) I was using a simple example:
> 
> #pragma unroll 2
>         for (i=0;i<6;i++)
>         {
>             printf ("Hello world\n");
>         }
> 
> If I do this, instead of transforming the code into :
>         for (i=0;i<3;i++)
>         {
>             printf ("Hello world\n");
>             printf ("Hello world\n");
>         }
> 
> as we could expect, it is transformed into:
>         for (i=0;i<2;i++)
>         {
>             printf ("Hello world\n");
>             printf ("Hello world\n");
>         }
>         for (i=0;i<2;i++)
>         {
>             printf ("Hello world\n");
>         }
> 
> 
> (I am using 4.3.2 currently)
> 
> I am using the tree_unroll_loop function to perform the unrolling and
> it seems to always want to keep that epilogue. Is there a reason for
> this? Or is this a bug of some sorts?

such an epilogue is needed when the # of iterations is not known in the
compile time; it should be fairly easy to modify the unrolling not to
emit it when it is not necessary,

Zdenek