llvm dev - Jun 2018 - Vectorization in multiple threads

Hello,
I want to create multiple threads and do vectorization in each. like if my
loop has 2048 iterations it should be divided first into threads like if 4
threads so each thread should do 512 iterations using vector instructions
of length 64.

how to achieve this? i have tried using #pragma omp parallel for simd and
compiled using following;

clang  -S -emit-llvm 1.c -march=knl -O3 -fopenmp -mllvm
-disable-llvm-optzns -o 1.ll
opt  -S -O3 -force-vector-width=64  1.ll -o 1_o3.ll

i m getting this error;

remark: <unknown>:0:0: loop not vectorized: could not determine number of
loop iterations
warning: <unknown>:0:0: loop not vectorized: failed explicitly specified
loop vectorization

How to resolve this?
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