[AddressLowering] Set new ParamDecl's specifier.

It's required that ParamDecl's that are synthesized have a specifier
set.  Set it to InOut, matching SILGen's behavior in
emitIndirectResultParameters.

Author: nate-chandler

lib/SILOptimizer/Mandatory/AddressLowering.cpp

@@ -135,6 +135,7 @@
 #define DEBUG_TYPE "address-lowering"
 
 #include "PhiStorageOptimizer.h"
+#include "swift/AST/Decl.h"
 #include "swift/Basic/BlotSetVector.h"
 #include "swift/Basic/Range.h"
 #include "swift/SIL/BasicBlockUtils.h"
@@ -559,6 +560,7 @@ static unsigned insertIndirectReturnArgs(AddressLoweringState &pass) {
     auto var = new (astCtx) ParamDecl(
         SourceLoc(), SourceLoc(), astCtx.getIdentifier("$return_value"),
         SourceLoc(), astCtx.getIdentifier("$return_value"), declCtx);
+    var->setSpecifier(ParamSpecifier::InOut);
 
     SILFunctionArgument *funcArg =
         pass.function->begin()->insertFunctionArgument(

test/SILOptimizer/opaque_values_O.swift

@@ -0,0 +1,11 @@
+// RUN: %target-swift-frontend -enable-sil-opaque-values -parse-as-library -emit-sil -O %s | %FileCheck %s
+
+// Verify the arguments.  When AccessPathVerification runs, it will be checked
+// that the ParamDecl that AddressLowering synthesizes has a specifier
+// (ParamSpecifier) set.
+// CHECK-LABEL: sil @$s15opaque_values_O3minyxx_xtSLRzlF : {{.*}} {
+// CHECK:       bb0(%0 : $*T, %1 : $*T, %2 : $*T):
+// CHECK-LABEL: } // end sil function '$s15opaque_values_O3minyxx_xtSLRzlF'
+public func min<T: Comparable>(_ x: T, _ y: T) -> T {
+  return y < x ? y : x
+}