[Panzerschrek]

Fil-C is only good if one needs to recompile an existing C program and gain extra safety without caring much about result performance. And even in such case I doubt it's useful, since existing code should be already well-tested and (almost) bug-free.

If new code needs to be written, there is no reason to use Fil-C, since better languages with build-in security mechanisms exist.

[ekaryotic]

could you recompile a c program in fil-c and then decompile it to c and recompile it in c to have the high performance.

[aw1621107]

The performance hit comes from the extra work Fil-C does over regular C, so if your decompilation/recompiliation process preserves semantics that extra work (and thus the performance hit) will remain in the final product.