英特尔编译器矢量化报告：重型开销与轻量级？

Question

在英特尔Fortran编译器的这个矢量化报告中：

LOOP BEGIN at MLFMATranslationProd.f90(38,2)
  remark #15399: vectorization support: unroll factor set to 4
  remark #15300: LOOP WAS VECTORIZED
  remark #15462: unmasked indexed (or gather) loads: 2
  remark #15475: --- begin vector loop cost summary ---
  remark #15476: scalar loop cost: 12
  remark #15477: vector loop cost: 20.000
  remark #15478: estimated potential speedup: 2.340
  remark #15479: lightweight vector operations: 5
  remark #15481: heavy-overhead vector operations: 1
  remark #15488: --- end vector loop cost summary ---
LOOP END

此处lightweight vector和heavy-overhead vector操作的含义是什么？

相关循环看起来像

do ir=1,N(lev) 
    G1(lev)%D(ir) = 0.d0 
    G2(lev)%D(ir) = 0.d0 
enddo

lev某个整数。