No.

LLVM is not amenable to using multiple threads to compile a single TU. The use-lists of global values (such as functions, global variables, or constant expressions) include all uses from all functions, so parallelizing on a per-function basis requires acquiring locks (or some sort of lock-free data structure) to add, remove, or iterate these lists, which would considerable overhead on a relatively common operation.

If you want more details, you can read the recent thread on llvm-dev discussing this: http://lists.llvm.org/pipermail/llvm-dev/2020-March/139606.h...

Lets certainly hope clang will eventually manage to improve things in that context, because the restriction against parallelization during the optimization step when there is a single compilation unit is quite punishing.

Doesn't clang already implement this ?

LLVM can process multiple codegen units in parallel already, and many frontends split TUs into multiple codegen units.