[SILGen] Fall back to module lookup on invalid conformance when building subst. maps for vtable thunks

Author: AnthonyLatsis

include/swift/AST/SubstitutionMap.h

@@ -111,8 +111,30 @@ class SubstitutionMap {
 
   /// Build an interface type substitution map for the given generic
   /// signature using the mapping in the given substitutions.
+  ///
+  /// \Note
+  /// Currently, \p fallBackToModuleConformanceLookup is only necessary
+  /// when we emit a reabstraction thunk for an override, because we might
+  /// not have enough information in the substitution map alone.
+  ///
+  /// For example, combining the override substitutions with the invocation
+  /// generic signature for the following override requires recovering
+  /// the implied conformance Foo : P.
+  ///
+  /// \code
+  /// class Base<T> {
+  ///   func foo<U>(u: U) where T == Foo {}
+  /// }
+  /// class Derived<T>: Base<T> {
+  ///   override func foo<U>(u: U) where T: P {}
+  /// }
+  /// \endcode
+  ///
+  /// \param fallBackToModuleConformanceLookup Fall back to module lookup
+  /// if a conformance could not be found otherwise.
   static SubstitutionMap get(GenericSignature genericSig,
-                             SubstitutionMap substitutions);
+                             SubstitutionMap substitutions,
+                             bool fallBackToModuleConformanceLookup = false);
 
   /// Build an interface type substitution map for the given generic signature
   /// from a type substitution function and conformance lookup function.

lib/AST/SubstitutionMap.cpp

@@ -178,19 +178,49 @@ SubstitutionMap SubstitutionMap::getCanonical() const {
 
 
 SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
-                                     SubstitutionMap substitutions) {
+                                     SubstitutionMap substitutions,
+                                     bool fallBackToModuleConformanceLookup) {
   if (!genericSig) {
     assert(!substitutions.hasAnySubstitutableParams() &&
            "Shouldn't have substitutions here");
     return SubstitutionMap();
   }
 
+  LookupConformanceFn lookupConformanceFn;
+  if (fallBackToModuleConformanceLookup) {
+    /// Like \c LookUpConformanceInSubstitutionMap , but falls back to module
+    /// lookup if the conformance could not be found.
+    class LookUpConformanceInSubstitutionMapOrModule {
+      SubstitutionMap Subs;
+    public:
+      LookUpConformanceInSubstitutionMapOrModule(SubstitutionMap Subs)
+          : Subs(Subs) {}
+
+      ProtocolConformanceRef operator()(CanType dependentType,
+                                        Type conformingReplacementType,
+                                        ProtocolDecl *conformedProtocol) const {
+        auto conformance = LookUpConformanceInSubstitutionMap(Subs)
+            (dependentType, conformingReplacementType, conformedProtocol);
+
+        if (conformance.isInvalid())
+          return conformedProtocol->getParentModule()->lookupConformance(
+                     conformingReplacementType, conformedProtocol);
+        return conformance;
+      };
+    };
+
+    lookupConformanceFn =
+        LookUpConformanceInSubstitutionMapOrModule(substitutions);
+  } else {
+    lookupConformanceFn = LookUpConformanceInSubstitutionMap(substitutions);
+  }
+
   return SubstitutionMap::get(genericSig,
            [&](SubstitutableType *type) -> Type {
              return substitutions.lookupSubstitution(
                       CanSubstitutableType(type));
            },
-           LookUpConformanceInSubstitutionMap(substitutions));
+           lookupConformanceFn);
 }
 
 /// Build an interface type substitution map for the given generic signature

lib/SILGen/SILGenPoly.cpp

@@ -3744,7 +3744,8 @@ SILGenFunction::emitVTableThunk(SILDeclRef base,
 
   auto subs = getForwardingSubstitutionMap();
   if (auto genericSig = derivedFTy->getInvocationGenericSignature()) {
-    subs = SubstitutionMap::get(genericSig, subs);
+    subs = SubstitutionMap::get(genericSig, subs,
+                                /*fallBackToModuleConformanceLookup*/true);
 
     derivedFTy =
         derivedFTy->substGenericArgs(SGM.M, subs, getTypeExpansionContext());

test/SILGen/vtable_thunks_reabstraction.swift

@@ -484,11 +484,14 @@ class ConcreteOptional: Opaque<S?> {
 class GenericBase<T> {
   func doStuff<U>(t: T, u: U) {}
   init<U>(t: T, u: U) {}
+
+  func doStuff2<U>(u: U) where T == Int {}
 }
 
 // CHECK-LABEL: sil_vtable GenericBase {
 // CHECK-NEXT:   #GenericBase.doStuff!1: <T><U> (GenericBase<T>) -> (T, U) -> () : @$s27vtable_thunks_reabstraction11GenericBaseC7doStuff1t1uyx_qd__tlF        // GenericBase.doStuff<A>(t:u:)
 // CHECK-NEXT:   #GenericBase.init!allocator.1: <T><U> (GenericBase<T>.Type) -> (T, U) -> GenericBase<T> : @$s27vtable_thunks_reabstraction11GenericBaseC1t1uACyxGx_qd__tclufC
+// CHECK-NEXT:   #GenericBase.doStuff2!1: <T where T == Int><U> (GenericBase<T>) -> (U) -> () : @$s27vtable_thunks_reabstraction11GenericBaseC8doStuff21uyqd___tSiRszlF
 // CHECK-NEXT:   #GenericBase.deinit!deallocator.1: @$s27vtable_thunks_reabstraction11GenericBaseCfD     // GenericBase.__deallocating_deinit
 // CHECK-NEXT: }
 
@@ -504,6 +507,7 @@ class ConcreteSub : GenericBase<Int> {
 // CHECK-LABEL: sil_vtable ConcreteSub {
 // CHECK-NEXT:   #GenericBase.doStuff!1: <T><U> (GenericBase<T>) -> (T, U) -> () : @$s27vtable_thunks_reabstraction11ConcreteSubC7doStuff1t1uySi_xtlFAA11GenericBaseCAdeFyx_qd__tlFTV [override]        // vtable thunk for GenericBase.doStuff<A>(t:u:) dispatching to ConcreteSub.doStuff<A>(t:u:)
 // CHECK-NEXT:   #GenericBase.init!allocator.1: <T><U> (GenericBase<T>.Type) -> (T, U) -> GenericBase<T> : @$s27vtable_thunks_reabstraction11ConcreteSubC1t1uACSi_xtclufCAA11GenericBaseCAdeGyxGx_qd__tclufCTV [override]
+// CHECK-NEXT:   #GenericBase.doStuff2!1: <T where T == Int><U> {{.*}}F [inherited]
 // CHECK-NEXT:   #ConcreteSub.deinit!deallocator.1: @$s27vtable_thunks_reabstraction11ConcreteSubCfD     // ConcreteSub.__deallocating_deinit
 // CHECK-NEXT: }
 
@@ -543,6 +547,7 @@ class MoreGenericSub1<T, TT> : GenericBase<T> {
 // CHECK-LABEL: sil_vtable MoreGenericSub1 {
 // CHECK-NEXT:   #GenericBase.doStuff!1: <T><U> (GenericBase<T>) -> (T, U) -> () : @$s27vtable_thunks_reabstraction15MoreGenericSub1C7doStuff1t1uyx_qd__tlF [override] // MoreGenericSub1.doStuff<A>(t:u:)
 // CHECK-NEXT:   #GenericBase.init!allocator.1: <T><U> (GenericBase<T>.Type) -> (T, U) -> GenericBase<T> : @$s27vtable_thunks_reabstraction15MoreGenericSub1C1t1uACyxq_Gx_qd__tclufC [override]
+// CHECK-NEXT:   #GenericBase.doStuff2!1: <T where T == Int><U> {{.*}}F [inherited]
 // CHECK-NEXT:   #MoreGenericSub1.deinit!deallocator.1: @$s27vtable_thunks_reabstraction15MoreGenericSub1CfD     // MoreGenericSub1.__deallocating_deinit
 // CHECK-NEXT: }
 
@@ -555,5 +560,18 @@ class MoreGenericSub2<TT, T> : GenericBase<T> {
 // CHECK-LABEL: sil_vtable MoreGenericSub2 {
 // CHECK-NEXT:   #GenericBase.doStuff!1: <T><U> (GenericBase<T>) -> (T, U) -> () : @$s27vtable_thunks_reabstraction15MoreGenericSub2C7doStuff1t1uyq__qd__tlF [override]        // MoreGenericSub2.doStuff<A>(t:u:)
 // CHECK-NEXT:   #GenericBase.init!allocator.1: <T><U> (GenericBase<T>.Type) -> (T, U) -> GenericBase<T> : @$s27vtable_thunks_reabstraction15MoreGenericSub2C1t1uACyxq_Gq__qd__tclufC [override]
+// CHECK-NEXT:   #GenericBase.doStuff2!1: <T where T == Int><U> {{.*}}F [inherited]
 // CHECK-NEXT:   #MoreGenericSub2.deinit!deallocator.1: @$s27vtable_thunks_reabstraction15MoreGenericSub2CfD     // MoreGenericSub2.__deallocating_deinit
 // CHECK-NEXT: }
+
+class GenericSub2<T>: GenericBase<T> {
+  override func doStuff2<U>(u: U) where T: FixedWidthInteger {}
+}
+
+// CHECK-LABEL: sil_vtable GenericSub2 {
+// CHECK-NEXT:   #GenericBase.doStuff!1: <T><U> {{.*}}F [inherited]
+// CHECK-NEXT:   #GenericBase.init
+// CHECK-NEXT:   #GenericBase.doStuff2!1: <T where T == Int><U> (GenericBase<T>) -> (U) -> () : @$s27vtable_thunks_reabstraction11GenericSub2C8doStuff21uyqd___ts17FixedWidthIntegerRzlFAA0D4BaseCAdEyqd___tSiRszlFTV [override]
+// CHECK-NEXT:   #GenericSub2.doStuff2!1: <T where T : FixedWidthInteger><U> (GenericSub2<T>) -> (U) -> () : @$s27vtable_thunks_reabstraction11GenericSub2C8doStuff21uyqd___ts17FixedWidthIntegerRzlF
+// CHECK-NEXT:   #GenericSub2.deinit
+// CHECK-NEXT: }