[SILGen] Add support thunk support for () -> T to () -> Void conversions

(cherry picked from commit cddb821)

Author: xedin

lib/SILGen/SILGenPoly.cpp

@@ -1565,6 +1565,9 @@ class ResultPlanner {
       ///
       /// Valid: reabstraction info, InnerResult, OuterResult.
       ReabstractDirectToDirect,
+
+      /// Ignore the next direct inner result, since the outer is 'Void'.
+      IgnoreDirectResult,
     };
 
     Operation(Kind kind) : TheKind(kind) {}
@@ -1709,6 +1712,24 @@ class ResultPlanner {
                                     SILResultInfo outerResult,
                                     SILValue optOuterResultAddr);
 
+  void planIgnoredResult(AbstractionPattern innerOrigType,
+                         CanType innerSubstType, PlanData &planData) {
+    if (innerOrigType.isTuple()) {
+      auto innerSubstTuple = cast<TupleType>(innerSubstType);
+      for (unsigned i = 0, n = innerSubstTuple->getNumElements(); i != n; ++i)
+        planIgnoredResult(innerOrigType.getTupleElementType(i),
+                          innerSubstTuple.getElementType(i), planData);
+      return;
+    }
+
+    auto innerResult = claimNextInnerResult(planData);
+    if (innerResult.isFormalIndirect() &&
+        SGF.silConv.isSILIndirect(innerResult))
+      (void)addInnerIndirectResultTemporary(planData, innerResult);
+    else
+      addIgnoreDirectResult();
+  }
+
   /// Claim the next inner result from the plan data.
   SILResultInfo claimNextInnerResult(PlanData &data) {
     return claimNext(data.InnerResults);
@@ -1858,6 +1879,10 @@ class ResultPlanner {
     op.OuterOrigType = outerOrigType;
     op.OuterSubstType = outerSubstType;
   }
+
+  void addIgnoreDirectResult() {
+    (void)addOperation(Operation::IgnoreDirectResult);
+  }
 };
 
 } // end anonymous namespace
@@ -1868,6 +1893,13 @@ void ResultPlanner::plan(AbstractionPattern innerOrigType,
                          AbstractionPattern outerOrigType,
                          CanType outerSubstType,
                          PlanData &planData) {
+  // Conversion from `() -> T` to `() -> Void` is allowed when
+  // the argument is a closure.
+  if (!innerSubstType->isVoid() && outerSubstType->isVoid()) {
+    planIgnoredResult(innerOrigType, innerSubstType, planData);
+    return;
+  }
+
   // The substituted types must match up in tuple-ness and arity.
   assert(isa<TupleType>(innerSubstType) == isa<TupleType>(outerSubstType) ||
          (isa<TupleType>(innerSubstType) &&
@@ -2580,6 +2612,10 @@ void ResultPlanner::execute(ArrayRef<SILValue> innerDirectResults,
     case Operation::InjectOptionalIndirect:
       SGF.B.createInjectEnumAddr(Loc, op.OuterResultAddr, op.SomeDecl);
       continue;
+
+    case Operation::IgnoreDirectResult:
+      (void)claimNext(innerDirectResults);
+      continue;
     }
     llvm_unreachable("bad operation kind");
   }

test/IRGen/objc_retainAutoreleasedReturnValue.swift

@@ -24,13 +24,15 @@ public func test(_ dict: NSDictionary) {
 // popq   %rbp  ;<== Blocks the handshake from objc_autoreleaseReturnValue
 // jmp    0x01ec20 ; symbol stub for: objc_retainAutoreleasedReturnValue
 
-// CHECK-LABEL: define {{.*}}swiftcc void @"$S34objc_retainAutoreleasedReturnValue4testyySo12NSDictionaryCFyADcfU_"(%TSo12NSDictionaryC*)
+// CHECK-LABEL: define {{.*}}swiftcc %TSo12NSEnumeratorC* @"$S34objc_retainAutoreleasedReturnValue4testyySo12NSDictionaryCFSo12NSEnumeratorCADcfU_"(%TSo12NSDictionaryC*)
 // CHECK: entry:
 // CHECK:   call {{.*}}@objc_msgSend
 // CHECK:   notail call i8* @objc_retainAutoreleasedReturnValue
-// CHECK:   ret void
+// CHECK:   ret %TSo12NSEnumeratorC*
 
-// OPT-LABEL: define {{.*}}swiftcc void @"$S34objc_retainAutoreleasedReturnValue4testyySo12NSDictionaryCFyADcfU_"(%TSo12NSDictionaryC*)
+// CHECK-LABEL: define {{.*}}swiftcc void @"$SSo12NSDictionaryCSo12NSEnumeratorCIgxo_ABIgx_TR"(%TSo12NSDictionaryC*, i8*, %swift.refcounted*)
+
+// OPT-LABEL: define {{.*}}swiftcc void @"$S34objc_retainAutoreleasedReturnValue10useClosureyySo12NSDictionaryC_yADctF06$SSo12h43CSo12NSEnumeratorCIgxo_ABIgx_TR049$S34objc_bcD41Value4testyySo12a6CFSo12B7CADcfU_Tf3npf_nTf1nc_nTf4g_n"(%TSo12NSDictionaryC*)
 // OPT: entry:
 // OPT:   call {{.*}}@objc_msgSend
 // OPT:   notail call i8* @objc_retainAutoreleasedReturnValue