Doing so speeds up psi2ir ~2 times, and thus improves total compiler
performance by about 6-8%.
Unless JVM IR is in the mode where linking via signatures is the only
way (-Xserialize-ir, -Xklib), signatures are actually not needed at all,
SymbolTable can use the frontend representation (descriptors for FE1.0,
and hopefully FIR elements for K2) as hash table keys. The only catch is
that since other backends still need to work with signatures, all the
common IR utilities, such as irTypePredicates.kt, need to work correctly
for IR elements both with signatures and without.
Also, introduce a fallback compiler flag -Xlink-via-signatures, in case
something goes wrong, to be able to troubleshoot and workaround any
issues.
#KT-48233
Alexander Udalov
6379fe4c4c