How to enable Loop tiling in gcc?

How to compile a code using gcc, which performs loop tiling (Blocking) ? The -O3开发者_JAVA技巧 optimization by default does not do loop tiling. I need to enable loop tiling in this flag and also, find out the tile factor. (E.g. cubic tiling or rectangular tiling) i.e. the internal tiling heuristics .

Thanks

You haven't provided the exact version of gcc, nor example code, nor result code, nor did you look hard enough at the internet, but possibly this already answers your question:

Strip mining is an optimization that has been introduced into gcc with the merge of the graphite branch in version 4.4. See also the manual:

-floop-strip-mine Perform loop strip mining transformations on loops. Strip mining splits a loop into two nested loops. The outer loop has strides equal to the strip size and the inner loop has strides of the original loop within a strip. The strip length can be changed using the loop-block-tile-size parameter. For example, given a loop like:

          DO I = 1, N
            A(I) = A(I) + C
          ENDDO

loop strip mining will transform the loop as if the user had written:

          DO II = 1, N, 51
            DO I = II, min (II + 50, N)
              A(I) = A(I) + C
            ENDDO
          ENDDO

This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with --with-ppl and --with-cloog to enable the Graphite loop transformation infrastructure.

You may run man gcc | grep '\-floop\-strip\-mine' to check if that is a supported option. For the exact gcc version, type gcc --version.