This patch takes into account a corner case available for loops
over a progression (see backend.native/tests/external/codegen/box/
ranges/forInUntil/forInUntilMinint.kt test):
for (i in 0 until Int.MIN_VALUE) { ... }
Here we cannot use subtraction to obtain a right bound of the loop
due to an overflow. Instead we consider any loop with MIN_VALUE in
it's right bound as empty loop. Such behaviour is similar to the one
of 'until' method.
So now the empty check for a loops with 'until' call:
for (i in first until bound) { ... }
is as follows:
val last = getProgressionLast(first, bound, step) // Only if step==1
if (first <= last && bound > <Int|Long|Char>.MIN_VALUE) {
do { ... } while(i != last)
}
Further improvements: We can generate a simpler IR for some simple
frequent cases (e.g. for until calls without steps) and eliminate
loops if we can prove that they are empty.
Ilya Matveev