为什么某些数组在 Fortran 中没有正确对齐以进行矢量化？

如何解决为什么某些数组在 Fortran 中没有正确对齐以进行矢量化？

我正在尝试通过向量化 for 循环来改进 Fortran 77 代码。我对矢量化还很陌生，虽然我可以让代码进行矢量化，但优化报告告诉我，我的某些数组具有未对齐的访问权限。据我所知，这使得矢量化效率降低。我已手动向数组添加填充以对齐数据，这似乎适用于我的大多数数组，但不适用于所有数组（请参阅示例代码）。

      SUbroUTINE SOURCE
      ParaMETER(NLInes=8)
      ParaMETER(NLM=NLInes-1)
      ParaMETER(NZ=18)
      
      COMMON/TEST/h(-nlines:nlines+15,-nlines:nlines)
     &,hr(-nlines:nlines+15,-nlines:nlines)
      COMMON/PRO/P2(-nlm:nlm+1,-nlm:nlm)

      dimension SNT(-nlm:nlm+1,-nlm:nlm,0:NZ+1)

      DO iy=-nlm,nlm
       DO ix=-nlm,nlm
        H(ix,iy)=SNT(ix,iy,1)
     &  +SNT(ix,0)
     &  +SNT(ix,2)

        HR(ix,iy)=P2(ix,iy)*H(ix,iy)
       enddo
      enddo      
      END

以及优化报告的相关部分：

   LOOP BEGIN at SOURCE.FPP(13,8)
      remark #15389: vectorization support: reference h(ix,iy) has unaligned access   [ SOURCE.FPP(14,9) ]
      remark #15388: vectorization support: reference snt(ix,1) has aligned access   [ SOURCE.FPP(14,0) has aligned access   [ SOURCE.FPP(14,2) has aligned access   [ SOURCE.FPP(15,9) ]
      remark #15389: vectorization support: reference hr(ix,iy) has unaligned access   [ SOURCE.FPP(18,9) ]
      remark #15388: vectorization support: reference p2(ix,iy) has aligned access   [ SOURCE.FPP(18,9) ]
      remark #15389: vectorization support: reference h(ix,9) ]
      remark #15381: vectorization support: unaligned access used inside loop body
      remark #15305: vectorization support: vector length 4
      remark #15399: vectorization support: unroll factor set to 3
      remark #15300: LOOP WAS VECTORIZED
      remark #15448: unmasked aligned unit stride loads: 4 
      remark #15450: unmasked unaligned unit stride loads: 1 
      remark #15451: unmasked unaligned unit stride stores: 2 
      remark #15475: --- begin vector cost summary ---
      remark #15476: scalar cost: 15 
      remark #15477: vector cost: 4.250 
      remark #15478: estimated potential speedup: 2.340 
      remark #15488: --- end vector cost summary ---
      remark #25456: Number of Array Refs Scalar Replaced In Loop: 3
      remark #25015: Estimate of max trip count of loop=1
   LOOP END

为什么 h(ix,iy) 和 hr(ix,iy) 没有对齐访问？以及如何对齐它们以获得更好的矢量化？

可能还有相关信息：

Intel(R) Fortran Intel(R) 64 Compiler for applications running on Intel(R) 64,Version 19.0.0.117 Build 20180804

Compiler options: -qopt-report=5 -c -DLINUX -O3 -w -assume nounderscore -xcore-AVX2 -o SOURCE.o193

提前感谢您的时间和帮助！

为什么某些数组在 Fortran 中没有正确对齐以进行矢量化？

如何解决为什么某些数组在 Fortran 中没有正确对齐以进行矢量化？

相关推荐