KT-15862 Inline generic functions can unexpectedly box primitives

Previous version of the boxing/unboxing analysis treated merging boxed and non-boxed values as a hazard.
If such merged values are not used (e.g., early return + local variables reused in inlined calls),
corresponding boxing/unboxing operations still can be optimized out.

All information related to boxed value usage by instructions is moved to 'BoxedValueDescriptor'.
Introduce "tainted" (and "clean") boxed values, with the following rules:

  merge(B, B) = B, if unboxed types are compatible,
                T, otherwise

  merge(B, X) = T

  merge(T, X) = T

  where
    X is a non-boxed value,
    B is a "clean" boxed value,
    T is a "tainted" boxed value.

Postpone decision about value merge hazards until a "tainted" value is used.

compiler/testData/codegen/box/boxingOptimization/taintedValues.kt

@@ -0,0 +1,11 @@
+// WITH_RUNTIME
+
+// Just make sure there's no VerifyError
+
+fun getOrElse() =
+        mapOf<String, Int>().getOrElse("foo") { 3 }
+
+fun isNotEmpty(l: ArrayList<Int>) =
+        l.iterator()?.hasNext() ?: false
+
+fun box() = "OK"

compiler/testData/codegen/box/boxingOptimization/taintedValuesBox.kt

@@ -0,0 +1,49 @@
+// WITH_RUNTIME
+
+inline fun <T> put(
+        x: T,
+        maxExclusive: Int,
+        isEmpty: (Int) -> Boolean,
+        equals: (T, T) -> Boolean,
+        fetch: (Int) -> T,
+        store: (Int, T) -> Unit
+): Boolean {
+    var i = 0
+    do {
+        if (isEmpty(i)) {
+            store(i, x)
+            return true
+        }
+
+        val y = fetch(i)
+        if (equals(x, y)) {
+            return false
+        }
+
+        i++
+        if (i >= maxExclusive) return false
+    } while (true)
+}
+
+const val SIZE = 16
+val arr = IntArray(SIZE) { -1 }
+
+fun putNonNegInt(x: Int) =
+        put(x, SIZE,
+            isEmpty = { arr[it] < 0 },
+            equals = { x, y -> x == y },
+            fetch = { arr[it] },
+            store = { i, x -> arr[i] = x }
+        )
+
+fun box(): String {
+    putNonNegInt(1)
+    putNonNegInt(2)
+    putNonNegInt(3)
+
+    if (arr[0] != 1) return "Fail, ${arr.toList().toString()}"
+    if (arr[1] != 2) return "Fail, ${arr.toList().toString()}"
+    if (arr[2] != 3) return "Fail, ${arr.toList().toString()}"
+
+    return "OK"
+}