Preliminary "opaque conformance" support in SIL

lib/IRGen/GenArchetype.cpp

@@ -173,19 +173,6 @@ llvm::Value *irgen::emitArchetypeWitnessTableRef(IRGenFunction &IGF,
   auto wtable = IGF.tryGetLocalTypeData(archetype, localDataKind);
   if (wtable) return wtable;
 
-  // It can happen with class constraints that Sema will consider a
-  // constraint to be abstract, but the minimized signature will
-  // eliminate it as concrete.  Handle this by performing a concrete
-  // lookup.
-  // TODO: maybe Sema shouldn't ever do this?
-  if (Type classBound = archetype->getSuperclass()) {
-    auto conformance =
-      IGF.IGM.getSwiftModule()->lookupConformance(classBound, protocol);
-    if (conformance && conformance->isConcrete()) {
-      return emitWitnessTableRef(IGF, archetype, *conformance);
-    }
-  }
-
   // If we don't have an environment, this must be an implied witness table
   // reference.
   // FIXME: eliminate this path when opened types have generic environments.

lib/ParseSIL/ParseSIL.cpp

@@ -4084,17 +4084,13 @@ bool SILParser::parseSILInstruction(SILBuilder &B) {
       P.diagnose(TyLoc, diag::sil_witness_method_not_protocol);
       return true;
     }
-    ProtocolConformanceRef Conformance(proto);
-    if (!isa<ArchetypeType>(LookupTy)) {
-      auto lookup = P.SF.getParentModule()->lookupConformance(LookupTy, proto);
-      if (!lookup) {
-        P.diagnose(TyLoc, diag::sil_witness_method_type_does_not_conform);
-        return true;
-      }
-      Conformance = ProtocolConformanceRef(*lookup);
+    auto conformance = P.SF.getParentModule()->lookupConformance(LookupTy, proto);
+    if (!conformance) {
+      P.diagnose(TyLoc, diag::sil_witness_method_type_does_not_conform);
+      return true;
     }
-    
-    ResultVal = B.createWitnessMethod(InstLoc, LookupTy, Conformance, Member,
+
+    ResultVal = B.createWitnessMethod(InstLoc, LookupTy, *conformance, Member,
                                       MethodTy);
     break;
   }

lib/SIL/SILVerifier.cpp

@@ -2396,10 +2396,7 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
       require(AMI->getTypeDependentOperands().empty(),
               "Should not have an operand for the opened existential");
     }
-    if (isa<ArchetypeType>(lookupType) || lookupType->isAnyExistentialType()) {
-      require(AMI->getConformance().isAbstract(),
-              "archetype or existential lookup should have abstract conformance");
-    } else {
+    if (!isa<ArchetypeType>(lookupType)) {
       require(AMI->getConformance().isConcrete(),
               "concrete type lookup requires concrete conformance");
       auto conformance = AMI->getConformance().getConcrete();

lib/SILGen/SILGenApply.cpp

@@ -590,18 +590,20 @@ class Callee {
     case Kind::WitnessMethod: {
       auto constantInfo = SGF.getConstantInfo(*constant);
 
-      auto proto = cast<ProtocolDecl>(
-        Constant.getDecl()->getDeclContext());
-      auto lookupType = getSubstFormalType()
-                            .getInput()
-                            ->getRValueInstanceType()
-                            ->getCanonicalType();
+      auto proto = cast<ProtocolDecl>(Constant.getDecl()->getDeclContext());
+      auto genericSig = cast<AbstractFunctionDecl>(Constant.getDecl())
+        ->getGenericSignature();
+      auto subMap = genericSig->getSubstitutionMap(Substitutions);
+      auto selfType = proto->getSelfInterfaceType()->getCanonicalType();
+      auto lookupType = selfType.subst(subMap)->getCanonicalType();
+      auto conformance = *subMap.lookupConformance(selfType, proto);
 
       SILValue fn;
 
       if (!constant->isForeign) {
+
         fn = SGF.B.createWitnessMethod(
-          Loc, lookupType, ProtocolConformanceRef(proto), *constant,
+          Loc, lookupType, conformance, *constant,
           constantInfo.getSILType());
       } else {
         fn = SGF.B.createObjCMethod(Loc, borrowedSelf->getValue(),