[Bug tree-optimization/19038] [4.0 Regression] out of ssa causing loops to have more than one BB

[rakdver at atrey dot karlin dot mff dot cuni dot cz]

------- Additional Comments From rakdver at atrey dot karlin dot mff dot cuni dot cz  2005-01-21 13:22 -------
Subject: Re:  [4.0 Regression] out of ssa causing loops to have more than one BB

> No, tree-ssa-live is quite right.  ivtmp.3_12 and ivtmp.3_20 are defined 
> and live at some common statements, so they conflict: 
>  
>   # BLOCK 1 
>   # PRED: 0 [88.4%]  (true,exec) 1 [89.0%]  (dfs_back,false,exec) 
>   # ivtmp.3_12 = PHI <0(0), ivtmp.3_20(1)>; 
> <L8>:; 
>   D.501_28 = &__BLNK__.array1[ivtmp.3_12]; 
>   #   __BLNK___11 = V_MAY_DEF <__BLNK___2>; 
>   *D.501_28 = 1.0e+0; 
>   ivtmp.3_20 = ivtmp.3_12 + 1; 
>   D.503_30 = D.457_4 - 1; 
>   D.504_31 = (<unnamed type>) D.503_30; 
>   D.505_32 = D.504_31 + 1; 
>   if (ivtmp.3_20 == D.505_32) goto <L12>; else goto <L8>; 
>   # SUCC: 2 [11.0%]  (loop_exit,true,exec) 1 [89.0%]  (dfs_back,false,exec) 
>  
>   # BLOCK 2 
>   # PRED: 1 [11.0%]  (loop_exit,true,exec) 
> <L12>:; 
>   D.497_22 = ivtmp.3_12 + 2; 
>   lsm_tmp.2_23 = (int4) D.497_22; 
>   #   j_7 = V_MUST_DEF <j_6>; 
>   j = lsm_tmp.2_23; 
>   # SUCC: 3 [100.0%]  (fallthru) 
>  
> Between "ivtmp.3_20 = ivtmp.3_12 + 1;" and "D.497_22 = ivtmp.3_12 + 2;" 
> both versions of ivtmp.3 are live.  I have not looked at what causes this, 
> but IMOH all passes should avoid letting induction variables escape a loop. 

There's not much to avoid -- the iv is simply used outside of the loop,
and we cannot do anything about it.

> Interesting note: I think "D.497_22 = ivtmp.3_12 + 2;" could be replaced 
> with "D.497_22 = ivtmp.3_20 + 1;" which would fix this problem. 

I think this is how it is immediately after ivopts (if not, it would be
a bug); but dom performs this replacement.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19038