* In blocks, discard the result of any statement that has a return
type other than void. This was previously done by wrapping each
statement into an "implicit Unit conversion" that was actually
compiled down to a stack pop instead. If an expression happened to
already have type Unit, however, such a conversion was not inserted,
resulting in a stray reference on the stack. These conversions are
now redundant and should probably be removed.
* In assignments and non-exhaustive conditionals, materialize a Unit
on the stack to avoid depth mismatches that trip up the bytecode
validator. Because such expressions are generally used at block level
(and, indeed, the frontend will reject a non-exhaustive conditional
used as an expression), combined with the above change this results
in no additional GETSTATIC opcodes, as they are immediately removed
by the peephole optimizer.
- A LINENUMEBER node is "dead" if the corresponding instruction interval
contains at least one "dead" bytecode instruction
and no live bytecode instructions
- Observable local variable lifetimes should be taken into account
when determining if a NOP is required for debugger.
Using basic constant propagation (only integer constants, no arithmetic
calculations), rewrite conditional jump instructions with constant
arguments.
This covers problem description in KT-17007.
Note that it also works transparently with inline functions.
Partial evaluation is required to cover more "advanced" cases.
As a side effect, this also covers KT-3098:
rewrite IF_ICMP<cmp_op>(x, 0) to IF<cmp0_op>(x).
