Now, milestones of major Kotlin releases (e.g. 1.6.0-M1) will NOT
generate prerelease binaries anymore.
The reason for that is it's proven to be quite a complicated process to
turn on IR_PRE_RELEASE after the release is branched, perform double
bootstrap and fix tests, and then do it again in reverse just before
release. With the new release cadence, we don't have that much time to
do it and verify that everything works as intended.
Note that this only removes the "global" prerelease flag. Compiler will
still generate prerelease binaries if a non-stable language version is
used. For example, Kotlin 1.6.0-M1 with `-language-version 1.7` will
generate prerelease binaries.
Looking for the primary constructor manually doesn't work if it's
private in the other module on JVM, because private declarations are
skipped in IrLazyClass.
Otherwise, R8 does not transform kotlin-reflect, failing bootstrap.
Leaving end label the same is safe, since we do not remove labels during
transformation.
Do not check, that all Unit predecessors are POPs. This is safe for the
same reason, as it is safe to allow some of ARETURN sources not be
suspension point results.
To elaborate, before Unit, the stack is empty. This is because if there
are multiple paths to Unit and at least one of them comes from POP after
suspension point (we are interested in this case only - otherwise, the
call is not tail-call), in path from said POP the stack is empty, since
after suspension point the stack contains only one element. Thus, the
stack in other paths leading to Unit has to be empty, otherwise, merge
operation is not possible and ASM will report error during analysis.
Since the stack is empty in all paths, we can hoist Unit and following
ARETURN to predecessors, effectively turning path from suspension point
to tail-call.
This ensures that the debugger always has a bytecode offset for
the line number of a break/continue so that you step there and
so that you can set breakpoints there.
The `nop` instruction is optimized out if it has no line number
information.
^KT-46450 Fixed
Dmitry Petrov