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From: "hubicka at ucw dot cz" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/17560] [4.0 Regression] Infinite recursion in tree-scalar-evolution with -Os
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------- Additional Comments From hubicka at ucw dot cz  2004-10-08 12:16 -------
Subject: Re:  [4.0 Regression] Infinite recursion in tree-scalar-evolution with -Os

> 
> ------- Additional Comments From sebastian dot pop at cri dot ensmp dot fr  2004-10-08 12:07 -------
> Subject: Re:  [4.0 Regression] Infinite recursion in tree-scalar-evolution with -Os
> 
> Here is what the code looks like at the level of my analyzer.
> 
> loop_0
> {
>   bb_0 (preds = {bb_-1}, succs = {bb_0bb_0})
>   {
>   <bb 0>:
>     if (i_4 != 0) goto <L0>; else goto <L6>;
> 
>   }
>   bb_1 (preds = {bb_0}, succs = {bb_1})
>   {
>   <L0>:;
>     i_7 = i_4 + 1;
> 
>   }
>   bb_2 (preds = {bb_5bb_1}, succs = {bb_2})
>   {
>     # i_1 = PHI <i_2(5), i_7(1)>;
>   L:;
>     goto <bb 4> (<L5>);
> 
>   }
>   bb_5 (preds = {bb_0bb_4}, succs = {bb_5bb_5})
>   {
>     # i_2 = PHI <i_4(0), i_1(4)>;
>   <L6>:;
>     if (i_2 != 1) goto L; else goto <L8>;
> 
>   }
>   bb_6 (preds = {bb_5}, succs = {bb_6})
>   {
>   <L8>:;
>     return;
> 
>   }
>   loop_1
>   {
>     bb_3 (preds = {bb_4}, succs = {bb_3})
>     {
>     <L4>:;
>       j_6 = j_3 + 1;
> 
>     }
>     bb_4 (preds = {bb_3bb_2}, succs = {bb_4bb_4})
>     {
>       # j_3 = PHI <0(2), j_6(3)>;
>     <L5>:;
>       if (j_3 < i_1) goto <L4>; else goto <L6>;
> 
>     }
>   }
> }
> 
> The problem is that we have a cycle "i_1 -> i_2 -> i_1" outside any
> loop, and I'm not sure about the semantics of this representation.  
> By the way, is this a valid SSA form?

It seems to me that this can definitly happen in the case of irreducible
regions...

Honza
> 
> 
> 
> -- 
> 
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17560
> 
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-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17560