[NFC] Fixup __shared propagation

Two minor fixes that affect propagation of the __shared bit

* Type canonicalization now preserves __shared.  This could
manifest as invalid references to SILDeclRefs with the
wrong signature.

* Function type lowering dispatches __shared tuples that are
not valid substitution targets through the @owned path in all
cases.

Author: CodaFi

lib/AST/Type.cpp

@@ -1123,8 +1123,12 @@ CanType TypeBase::getCanonicalType() {
     auto &ctx = function->getInput()->getASTContext();
     auto &mod = *ctx.TheBuiltinModule;
     Type inputTy = function->getInput()->getCanonicalType(sig, mod);
-    if (!AnyFunctionType::isCanonicalFunctionInputType(inputTy))
-      inputTy = ParenType::get(ctx, inputTy->getInOutObjectType(), ParameterTypeFlags().withInOut(inputTy->is<InOutType>()));
+    if (!AnyFunctionType::isCanonicalFunctionInputType(inputTy)) {
+      auto flags = ParameterTypeFlags().withInOut(inputTy->is<InOutType>());
+      if (auto parenTy = dyn_cast<ParenType>(function->getInput().getPointer()))
+        flags = flags.withShared(parenTy->getParameterFlags().isShared());
+      inputTy = ParenType::get(ctx, inputTy->getInOutObjectType(), flags);
+    }
     auto resultTy = function->getResult()->getCanonicalType(sig, mod);
 
     Result = GenericFunctionType::get(sig, inputTy, resultTy,
@@ -1142,7 +1146,10 @@ CanType TypeBase::getCanonicalType() {
     FunctionType *FT = cast<FunctionType>(this);
     Type In = FT->getInput()->getCanonicalType();
     if (!AnyFunctionType::isCanonicalFunctionInputType(In)) {
-      In = ParenType::get(In->getASTContext(), In->getInOutObjectType(), ParameterTypeFlags().withInOut(In->is<InOutType>()));
+      auto flags = ParameterTypeFlags().withInOut(In->is<InOutType>());
+      if (auto parenTy = dyn_cast<ParenType>(FT->getInput().getPointer()))
+        flags = flags.withShared(parenTy->getParameterFlags().isShared());
+      In = ParenType::get(In->getASTContext(), In->getInOutObjectType(), flags);
       assert(AnyFunctionType::isCanonicalFunctionInputType(In));
     }
     Type Out = FT->getResult()->getCanonicalType();

lib/SIL/SILFunctionType.cpp

@@ -486,6 +486,11 @@ enum class ConventionsKind : uint8_t {
       ParameterConvention convention;
       if (origType.getAs<InOutType>()) {
         convention = ParameterConvention::Indirect_Inout;
+      } else if (isa<TupleType>(substType) && !origType.isTypeParameter()) {
+        // Do not lower tuples @guaranteed.  This can create conflicts with
+        // substitutions for witness thunks e.g. we take $*(T, T)
+        // @in_guaranteed and try to substitute it for $*T.
+        return visit(origType, substType);
       } else if (isFormallyPassedIndirectly(origType, substType, substTL)) {
         if (rep == SILFunctionTypeRepresentation::WitnessMethod)
           convention = ParameterConvention::Indirect_In_Guaranteed;
@@ -586,7 +591,7 @@ enum class ConventionsKind : uint8_t {
         // materializable -- if it doesn't contain an l-value type -- then it's
         // a valid target for substitution and we should not expand it.
         if (!tty || (eltPattern.isTypeParameter() && !tty->hasInOutElement())) {
-          if (params[i].getParameterFlags().isShared()) {
+          if (params[i].isShared()) {
             visitSharedType(eltPattern, ty, extInfo.getSILRepresentation());
           } else {
             visit(eltPattern, ty);

test/SILGen/shared.swift

@@ -134,7 +134,5 @@ func owned_to_shared_conversion(_ f : (Int, ValueAggregate, RefAggregate) -> Voi
   return owned_to_shared_conversion { (trivial : __shared Int, val : __shared ValueAggregate, ref : __shared RefAggregate) in }
 }
 
-// TODO: Investigate a different lowering scheme than @owned.  Perhaps '@guaranteed $@callee_guaranteed'?
-
-// CHECK-LABEL: sil hidden @_T06shared0A17_closure_loweringyySi_AA14ValueAggregateVAA03RefE0CtcF : $@convention(thin) (@owned @callee_owned (Int, @owned ValueAggregate, @owned RefAggregate) -> ()) -> ()
+// CHECK-LABEL: sil hidden @_T06shared0A17_closure_loweringyySi_AA14ValueAggregateVAA03RefE0CtcF : $@convention(thin) (@guaranteed @callee_owned (Int, @owned ValueAggregate, @owned RefAggregate) -> ()) -> ()
 func shared_closure_lowering(_ f : __shared (Int, ValueAggregate, RefAggregate) -> Void) {}