Compiler unable to vectorize inner loop

Question

I have a very simple fortran loop, that sets some elements of an array to 0.0, as shown below:

!dir$ loop count min(128)
arr(1:max(start,someVar)) = 0.0

When I compile the file with ifort, the vectorization report says:

file.f90(60): (col. 5) remark: LOOP WAS VECTORIZED
file.f90(60): (col. 5) remark: loop was not vectorized: not inner loop

I tried using !dir$ simd before the loop, and it vectorized. But my question is: Why wasn't it vectorizing, or converted to memcpy or memset? It is clearly an inner loop.

Answer 1

After upgrading to ifort 15, the optimization report stated that the line was in fact converted to memset. I think the new memset code loops over the array, 'memset'-ing chunks at a time.