SIL: Forgot to pass SubstFlags::PreservePackExpansionLevel in one place

Author: slavapestov

lib/SIL/IR/SILTypeSubstitution.cpp

@@ -77,7 +77,9 @@ class SILTypeSubstituter :
                ProtocolConformanceRef(conformedProtocol),
                conformingReplacementType->getCanonicalType(),
                typeExpansionContext);
-      }, SubstFlags::SubstituteOpaqueArchetypes);
+      },
+      SubstFlags::SubstituteOpaqueArchetypes |
+      SubstFlags::PreservePackExpansionLevel);
   }
 
   // Substitute a function type.

validation-test/compiler_crashers_2_fixed/rdar110363503.swift

@@ -0,0 +1,54 @@
+// RUN: %target-swift-frontend -emit-ir %s -disable-availability-checking
+
+struct ZipCollection<each C: Collection> {
+  let c: (repeat each C)
+}
+
+extension ZipCollection: Collection {
+  struct Element {
+    var elt: (repeat each C.Element)
+  }
+
+  struct Index {
+    let i: (repeat each C.Index)
+  }
+
+  var startIndex: Index {
+    Index(i: (repeat (each c).startIndex))
+  }
+
+  var endIndex: Index {
+    Index(i: (repeat (each c).endIndex))
+  }
+
+  func index(after i: Index) -> Index {
+    Index(i: (repeat (each c).index(after: each i.i)))
+  }
+
+  subscript(index: Index) -> Element {
+    Element(elt: (repeat (each c)[each index.i]))
+  }
+}
+
+extension ZipCollection.Index: Equatable {
+  static func ==(lhs: Self, rhs: Self) -> Bool {
+    var result = true
+    repeat result = ((each lhs.i) == (each rhs.i)) && result
+    return result
+  }
+}
+
+extension ZipCollection.Index: Comparable {
+  static func <(lhs: Self, rhs: Self) -> Bool {
+    var result: Bool? = nil
+    func check<T: Comparable>(_ x: T, _ y: T) {
+      if result == nil {
+        if x == y { return }
+        if x < y { result = true }
+        if x > y { result = false }
+      }
+    }
+    repeat check(each lhs.i, each rhs.i)
+    return result ?? false
+  }
+}