[Bug tree-optimization/50698] pretending to create versioning for alias when not required

["vincenzo.innocente at cern dot ch" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50698

--- Comment #6 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 2011-10-15 13:40:31 UTC ---
I now moved to a more realistic case that can be reduced to this: 

void loop(float *  x, int n) {
  for (int i=0;i!=n; ++i)
    x[i]=x[i+n]+x[i+2*n];
}


and it creates aliases even if the memory region are clearly disjoint:
(used gcc version 4.7.0 20111015 (experimental) (GCC) )
keep here or open an other "enhancement request"?

2: versioning for alias required: can't determine dependence between *D.2199_12
and *D.2195_8
2: mark for run-time aliasing test between *D.2199_12 and *D.2195_8
2: versioning for alias required: can't determine dependence between *D.2205_18
and *D.2195_8
2: mark for run-time aliasing test between *D.2205_18 and *D.2195_8
2: Vectorizing an unaligned access.
2: Vectorizing an unaligned access.
2: Vectorizing an unaligned access.
2: vect_model_load_cost: unaligned supported by hardware.
2: vect_model_load_cost: inside_cost = 2, outside_cost = 0 .
2: vect_model_load_cost: unaligned supported by hardware.
2: vect_model_load_cost: inside_cost = 2, outside_cost = 0 .
2: vect_model_simple_cost: inside_cost = 1, outside_cost = 0 .
2: vect_model_store_cost: unaligned supported by hardware.
2: vect_model_store_cost: inside_cost = 2, outside_cost = 0 .
2: cost model: Adding cost of checks for loop versioning aliasing.

2: cost model: epilogue peel iters set to vf/2 because loop iterations are
unknown .
2: Cost model analysis: 
  Vector inside of loop cost: 7
  Vector outside of loop cost: 19
  Scalar iteration cost: 4
  Scalar outside cost: 1
  prologue iterations: 0
  epilogue iterations: 2
  Calculated minimum iters for profitability: 7

2:   Profitability threshold = 6


Vectorizing loop at Arena.cpp:2

2: Profitability threshold is 6 loop iterations.
2: create runtime check for data references *D.2199_12 and *D.2195_8
2: create runtime check for data references *D.2205_18 and *D.2195_8
2: created 2 versioning for alias checks.

2: LOOP VECTORIZED.
Arena.cpp:1: note: vectorized 1 loops in function.