Create phi argument for only non-empty direct result in epilog bb

Author: meg-gupta

lib/SILGen/SILGenEpilog.cpp

@@ -29,10 +29,12 @@ void SILGenFunction::prepareEpilog(Optional<Type> directResultType,
     // Set NeedsReturn for indirect or direct results. This ensures that SILGen
     // emits unreachable if there is no source level return.
     NeedsReturn = !(*directResultType)->isEqual(TupleType::getEmpty(getASTContext()));
-    for (auto directResult : fnConv.getDirectSILResults()) {
-      SILType resultType = F.getLoweredType(F.mapTypeIntoContext(
-          fnConv.getSILType(directResult, getTypeExpansionContext())));
-      epilogBB->createPhiArgument(resultType, OwnershipKind::Owned);
+    if (NeedsReturn) {
+      for (auto directResult : fnConv.getDirectSILResults()) {
+        SILType resultType = F.getLoweredType(F.mapTypeIntoContext(
+            fnConv.getSILType(directResult, getTypeExpansionContext())));
+        epilogBB->createPhiArgument(resultType, OwnershipKind::Owned);
+      }
     }
   }
 

test/SILGen/opaque_values_silgen.swift

@@ -375,3 +375,12 @@ func anon_read_only_capture(_ x: Int) -> Int {
   return ({ x })()
 }
 
+
+// CHECK-LABEL: sil private [ossa] @$s20opaque_values_silgen22testEmptyReturnClosureyyFyycyKXEfu_yycfU_ : $@convention(thin) @substituted <τ_0_0> () -> @out τ_0_0 for <()> {
+// CHECK-NOT: bb1 
+// CHECK-LABEL: } // end sil function '$s20opaque_values_silgen22testEmptyReturnClosureyyFyycyKXEfu_yycfU_'
+func testEmptyReturnClosure() {
+  func bar() {}
+  let b = nil ?? { bar() }
+}
+