In the desugaring for compound assignment to a collection element,
argument expression 'i' is mapped to value parameters 'iG' and 'iS' of
corresponding 'get' and 'set' operators.
In general, these value parameters can have different indices.
This requires extra machinery in argument generation - that is, to be
able to generate a particular expression argument using an arbitrary
callback. In the vast majority of the cases this callback will just use
the corresponding StatementGenerator to generate IR subtree for the
provided expression. In case of 'get' and 'set' operator calls for an
augmented assignment expression this will map corresponding argument
expressions to pregenerated temporary variables.
Thus, in the following context:
```
class A
operator fun A.get(vararg xs: Int) = 0
operator fun A.set(i: Int, j: Int, v: Int) {}
```
statement `a[1, 2] += 3` will be desugared as (in a really pseudo
Kotlin):
```
{
val tmp_array = a
val tmp_index0 = 1
val tmp_index1 = 2
tmp_array.set(
i = tmp_index0,
j = tmp_index1,
v = tmp_array.get(xs = [tmp_index0, tmp_index1]).plus(3)
)
}
```
NB in FE unsigned integer constants are now represented using signed
integer types (e.g., UInt constant actually holds an Int value).
So, in IR so far we also represent unsigned constant literals as
constant values of corresponding signed types, but with corresponding
unsigned type:
0xFFFF_FFFFu becomes 'CONST Int type=kotlin.UInt value=-1'
Such references require proper scope so that local symbols are bound.
Example:
```
fun <T> outer() {
abstract class ALocal<S : T> {
abstract fun bar()
}
class Local<S : T> : ALocal<S>() {
override fun bar() {}
}
}
```
Here local classes have type parameters with upper bounds depending on
function type parameters, and members overriding members in other local
classes.
This introduces the following IR built-in functions required for proper
implementation of the number comparisons:
- ieee754Equals(T, T): Boolean,
for each T in {Float?, Double?}
- less(T, T): Boolean
lessOrEqual(T, T): Boolean
greater(T, T): Boolean
greaterOrEqual(T, T): Boolean
for each T in {Int, Long, Float, Double}
Dmitry Petrov