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/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -473,6 +473,18 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             doTest(fileName);
         }
 
+        @TestMetadata("kt15862.kt")
+        public void testKt15862() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/boxingOptimization/kt15862.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("kt15862_2.kt")
+        public void testKt15862_2() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/boxingOptimization/kt15862_2.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt6842.kt")
         public void testKt6842() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/boxingOptimization/kt6842.kt");