try intersection of upper bounds as a suggestion

not each bound itself
while resolving constraint system

compiler/testData/diagnostics/tests/inference/upperBounds/intersectUpperBounds.kt

@@ -0,0 +1,30 @@
+package s
+
+trait In<in T>
+
+trait A
+trait B
+trait C: A, B
+
+fun <T> foo(in1: In<T>, in2: In<T>): T = throw Exception("$in1 $in2")
+
+fun test(inA: In<A>, inB: In<B>, inC: In<C>) {
+
+    <!TYPE_INFERENCE_CONFLICTING_SUBSTITUTIONS!>foo<!>(inA, inB)
+
+    val r = foo(inA, inC)
+    r: C
+
+    val c: C = foo(inA, inB)
+
+    use(c)
+}
+
+fun <T: C> bar(in1: In<T>): T = throw Exception("$in1")
+
+fun test(inA: In<A>) {
+    val r = bar(inA)
+    r: C
+}
+
+fun use(vararg a: Any?) = a

compiler/testData/diagnostics/tests/inference/upperBounds/nonNullUpperBound.kt

@@ -0,0 +1,13 @@
+fun <R : Any> unescape(value: Any): R? = throw Exception("$value")
+
+fun <T: Any> foo(v: Any): T? = unescape(v)
+
+//--------------
+
+trait A
+
+fun <R : A> unescapeA(value: Any): R? = throw Exception("$value")
+
+
+fun <T: A> fooA(v: Any): T? = unescapeA(v)
+