[silgen] Change argument emission to emit @_noImplicitCopy arguments in such a form that move checking works on it.

This means that one can pass around let moveOnly values using @_noImplicitCopy.

Author: gottesmm

lib/SILGen/SILGenProlog.cpp

@@ -275,9 +275,17 @@ struct ArgumentInitHelper {
     if (!argrv.getType().isAddress()) {
       if (SGF.getASTContext().SILOpts.EnableExperimentalLexicalLifetimes &&
           value->getOwnershipKind() == OwnershipKind::Owned) {
+        bool isNoImplicitCopy = false;
+        if (auto *arg = dyn_cast<SILFunctionArgument>(value))
+          isNoImplicitCopy = arg->isNoImplicitCopy();
         value =
             SILValue(SGF.B.createBeginBorrow(loc, value, /*isLexical*/ true));
         SGF.Cleanups.pushCleanup<EndBorrowCleanup>(value);
+        if (isNoImplicitCopy) {
+          value = SGF.B.emitCopyValueOperation(loc, value);
+          value = SGF.B.createMoveValue(loc, value);
+          SGF.enterDestroyCleanup(value);
+        }
       }
       SGF.B.createDebugValue(loc, value, varinfo);
     } else {

test/SILGen/noimplicitcopy_attr.swift

@@ -8,7 +8,5 @@ public class Klass {}
 // CHECK-SIL: bb0(%0 : @noImplicitCopy $Klass):
 
 public func arguments(@_noImplicitCopy _ x: Klass) -> Klass {
-    let y = x
-    let z = x
     return x
 }

test/SILOptimizer/move_only_checker.swift

@@ -357,3 +357,17 @@ public func aggGenericStructAccessField<T>(_ x: AggGenericStruct<T>) {
         print(x2.lhs)
     }
 }
+
+/////////////////////////////////
+// No Implicit Copy Attributes //
+/////////////////////////////////
+
+public func klassNoImplicitCopyArgument(@_noImplicitCopy _ x: Klass) -> Klass {
+    return x
+}
+
+public func klassNoImplicitCopyArgumentError(@_noImplicitCopy _ x: Klass) -> Klass { // expected-error {{'x' consumed more than once}}
+    let y = x // expected-note {{consuming use}}
+    print(y)
+    return x // expected-note {{consuming use}}
+}