The back end (optimizer and code generator) for Intel's current C/C++ and Fortran compilers uses a modified version of Multiflow IL0 as its intermediate language.
Clem Cole reminds me that the situation has changed since I retired from Intel in 2016. Intel has switched to a LLVM-based compiler back end. The migration to LLVM was just getting started when I retired. Intel has been contributing to LLVM, particularly in the areas of parallelization, loop transformation, and interprocedural optimization. Some of this technology has Multiflow roots.
-Paul W.