Fix SILGen's computation of default argument generator isolation

Author: rjmccall

include/swift/SIL/SILDeclRef.h

@@ -38,6 +38,7 @@ namespace swift {
   enum class EffectsKind : uint8_t;
   class AbstractFunctionDecl;
   class AbstractClosureExpr;
+  class ActorIsolation;
   class ValueDecl;
   class FuncDecl;
   class ClosureExpr;
@@ -498,6 +499,8 @@ struct SILDeclRef {
     return result;
   }
 
+  ActorIsolation getActorIsolation() const;
+
   /// True if the decl ref references a thunk from a natively foreign
   /// declaration to Swift calling convention.
   bool isForeignToNativeThunk() const;

lib/SIL/IR/SILDeclRef.cpp

@@ -1873,3 +1873,21 @@ bool SILDeclRef::isCalleeAllocatedCoroutine() const {
 
   return getASTContext().SILOpts.CoroutineAccessorsUseYieldOnce2;
 }
+
+ActorIsolation SILDeclRef::getActorIsolation() const {
+  // Deallocating destructor is always nonisolated. Isolation of the deinit
+  // applies only to isolated deallocator and destroyer.
+  if (kind == SILDeclRef::Kind::Deallocator) {
+    return ActorIsolation::forNonisolated(false);
+  }
+
+  // Default argument generators use the isolation of the initializer,
+  // not the general isolation of the function.
+  if (isDefaultArgGenerator()) {
+    auto param = getParameterAt(getDecl(), defaultArgIndex);
+    assert(param);
+    return param->getInitializerIsolation();
+  }
+
+  return getActorIsolationOfContext(getInnermostDeclContext());
+}

lib/SIL/IR/SILFunctionType.cpp

@@ -2419,32 +2419,7 @@ swift::getSILFunctionTypeActorIsolation(CanAnyFunctionType substFnInterfaceType,
   }
 
   if (constant) {
-    // TODO: It should to be possible to `getActorIsolation` if
-    // reference is to a decl instead of trying to get isolation
-    // from the reference kind, the attributes, or the context.
-
-    if (constant->kind == SILDeclRef::Kind::Deallocator) {
-      return ActorIsolation::forNonisolated(false);
-    }
-
-    if (auto *decl = constant->getAbstractFunctionDecl()) {
-      if (auto *nonisolatedAttr =
-              decl->getAttrs().getAttribute<NonisolatedAttr>()) {
-        if (nonisolatedAttr->isNonSending())
-          return ActorIsolation::forCallerIsolationInheriting();
-      }
-
-      if (decl->getAttrs().hasAttribute<ConcurrentAttr>()) {
-        return ActorIsolation::forNonisolated(false /*unsafe*/);
-      }
-    }
-
-    if (auto *closure = constant->getAbstractClosureExpr()) {
-      if (auto isolation = closure->getActorIsolation())
-        return isolation;
-    }
-
-    return getActorIsolationOfContext(constant->getInnermostDeclContext());
+    return constant->getActorIsolation();
   }
 
   if (substFnInterfaceType->hasExtInfo() &&

lib/SILGen/SILGen.cpp

@@ -768,32 +768,6 @@ static bool isEmittedOnDemand(SILModule &M, SILDeclRef constant) {
   return false;
 }
 
-static ActorIsolation getActorIsolationForFunction(SILFunction &fn) {
-  if (auto constant = fn.getDeclRef()) {
-    if (constant.kind == SILDeclRef::Kind::Deallocator) {
-      // Deallocating destructor is always nonisolated. Isolation of the deinit
-      // applies only to isolated deallocator and destroyer.
-      return ActorIsolation::forNonisolated(false);
-    }
-
-    // If we have a closure expr, check if our type is
-    // nonisolated(nonsending). In that case, we use that instead.
-    if (auto *closureExpr = constant.getAbstractClosureExpr()) {
-      if (auto actorIsolation = closureExpr->getActorIsolation())
-        return actorIsolation;
-    }
-
-    // If we have actor isolation for our constant, put the isolation onto the
-    // function. If the isolation is unspecified, we do not return it.
-    if (auto isolation =
-            getActorIsolationOfContext(constant.getInnermostDeclContext()))
-      return isolation;
-  }
-
-  // Otherwise, return for unspecified.
-  return ActorIsolation::forUnspecified();
-}
-
 SILFunction *SILGenModule::getFunction(SILDeclRef constant,
                                        ForDefinition_t forDefinition) {
   // If we already emitted the function, return it.
@@ -820,7 +794,7 @@ SILFunction *SILGenModule::getFunction(SILDeclRef constant,
       });
 
   F->setDeclRef(constant);
-  F->setActorIsolation(getActorIsolationForFunction(*F));
+  F->setActorIsolation(constant.getActorIsolation());
 
   assert(F && "SILFunction should have been defined");
 
@@ -1316,7 +1290,7 @@ void SILGenModule::preEmitFunction(SILDeclRef constant, SILFunction *F,
   F->setDeclRef(constant);
 
   // Set our actor isolation.
-  F->setActorIsolation(getActorIsolationForFunction(*F));
+  F->setActorIsolation(constant.getActorIsolation());
 
   LLVM_DEBUG(llvm::dbgs() << "lowering ";
              F->printName(llvm::dbgs());