How to activate instruction scheduling in GCC?

Hi ALL

I'm a pure beginner in GCC, and currently working on a project to implement instruction scheduling for a new DSP processor. This processor doesn't have pipeline interlock, so the compiler HAVE to schedule the instruction without relying on hardware help anymore ....

The problem is, I'm a very beginner in GCC. I think the scheduling in GCC is activated by INSN_SCHEDULING variable (in automatically generated file: insn-attr.h), but I don't even know how to  activate this variable.

Any help would be appreciated....