[Key paths] Map Hashable conformances for subscript indexes out of context.

When SILGen maps the subscript indices used in a keypath out of context,
also map the conformance to Hashable. Fixes rdar://problem/46632723.

Author: DougGregor

lib/SILGen/SILGenExpr.cpp

@@ -3329,6 +3329,48 @@ lowerKeyPathSubscriptIndexTypes(
   }
 };
 
+/// Map the given protocol conformance out of context, replacing archetypes
+/// with their corresponding interface types.
+static ProtocolConformance *mapConformanceOutOfContext(
+                                         ProtocolConformance *conformance) {
+  if (!conformance->getType()->hasArchetype())
+    return conformance;
+
+  ASTContext &ctx = conformance->getProtocol()->getASTContext();
+  switch (conformance->getKind()) {
+  case ProtocolConformanceKind::Normal:
+  case ProtocolConformanceKind::Self:
+    llvm_unreachable("Normal and self conformances never have archetypes");
+
+  case ProtocolConformanceKind::Inherited: {
+    auto inherited = cast<InheritedProtocolConformance>(conformance);
+    return ctx.getInheritedConformance(
+             inherited->getType()->mapTypeOutOfContext(),
+             mapConformanceOutOfContext(inherited->getInheritedConformance()));
+  }
+
+  case ProtocolConformanceKind::Specialized: {
+    auto specialized = cast<SpecializedProtocolConformance>(conformance);
+    return ctx.getSpecializedConformance(
+             specialized->getType()->mapTypeOutOfContext(),
+             mapConformanceOutOfContext(specialized->getGenericConformance()),
+             specialized->getSubstitutionMap()
+               .mapReplacementTypesOutOfContext());
+  }
+  }
+}
+
+/// Map the given protocol conformance out of context, replacing archetypes
+/// with their corresponding interface types.
+static ProtocolConformanceRef mapConformanceOutOfContext(
+                                          ProtocolConformanceRef conformance) {
+  if (conformance.isAbstract())
+    return conformance;
+
+  return ProtocolConformanceRef(
+                        mapConformanceOutOfContext(conformance.getConcrete()));
+}
+
 static void
 lowerKeyPathSubscriptIndexPatterns(
                  SmallVectorImpl<KeyPathPatternComponent::Index> &indexPatterns,
@@ -3339,10 +3381,9 @@ lowerKeyPathSubscriptIndexPatterns(
     CanType formalTy;
     SILType loweredTy;
     std::tie(formalTy, loweredTy) = indexTypes[i];
-    auto hashable = indexHashables[i];
+    auto hashable = mapConformanceOutOfContext(indexHashables[i]);
     assert(hashable.isAbstract() ||
-           hashable.getConcrete()->getType()->mapTypeOutOfContext()
-                                 ->isEqual(formalTy));
+           hashable.getConcrete()->getType()->isEqual(formalTy));
 
     indexPatterns.push_back({baseOperand++, formalTy, loweredTy, hashable});
   }

test/IRGen/keypath_subscript.swift

@@ -0,0 +1,17 @@
+// RUN: %target-swift-frontend -emit-ir %s | %FileCheck %s
+
+// rdar://problem/46632723
+public struct Foo<T>: Hashable { }
+
+public struct Bar<U, V> {
+  public subscript<W> (foo: W) -> Int {
+    return 0
+  }
+
+  // CHECK-LABEL: define {{.*}} @"$s17keypath_subscript3FooVyqd__Gr0__lTh"
+  // CHECK: call swiftcc %swift.metadata_response @"$s17keypath_subscript3FooVMa"
+  public func blah<W>(_: W) -> AnyKeyPath {
+    return \Bar<U, V>.[Foo<W>()] as AnyKeyPath
+  }
+}
+