[borrow-expr] Wire up borrow expr to SILGenApply.

Author: gottesmm

include/swift/AST/DiagnosticsSema.def

@@ -6638,6 +6638,8 @@ ERROR(moveOnly_not_allowed_here,none,
       "'moveOnly' may only be applied to classes, structs, and enums", ())
 ERROR(move_expression_not_passed_lvalue,none,
       "'move' can only be applied to lvalues", ())
+ERROR(borrow_expression_not_passed_lvalue,none,
+      "'borrow' can only be applied to lvalues", ())
 
 //------------------------------------------------------------------------------
 // MARK: Type Wrappers

lib/SILGen/ArgumentSource.h

@@ -224,6 +224,7 @@ class ArgumentSource {
 
   Expr *findStorageReferenceExprForBorrow() &&;
   Expr *findStorageReferenceExprForMoveOnlyBorrow(SILGenFunction &SGF) &&;
+  Expr *findStorageReferenceExprForBorrowExpr(SILGenFunction &SGF) &&;
 
   /// Given that this source is an expression, extract and clear
   /// that expression.

lib/SILGen/SILGenApply.cpp

@@ -2968,6 +2968,29 @@ Expr *ArgumentSource::findStorageReferenceExprForMoveOnlyBorrow(
   return lvExpr;
 }
 
+Expr *
+ArgumentSource::findStorageReferenceExprForBorrowExpr(SILGenFunction &SGF) && {
+  if (!isExpr())
+    return nullptr;
+
+  auto argExpr = asKnownExpr();
+  auto *li = dyn_cast<LoadExpr>(argExpr);
+  if (!li)
+    return nullptr;
+  auto *borrowExpr = dyn_cast<BorrowExpr>(li->getSubExpr());
+  if (!borrowExpr)
+    return nullptr;
+
+  auto *lvExpr = ::findStorageReferenceExprForBorrow(borrowExpr->getSubExpr());
+
+  // Claim the value of this argument.
+  if (lvExpr) {
+    (void)std::move(*this).asKnownExpr();
+  }
+
+  return lvExpr;
+}
+
 Expr *ArgumentSource::findStorageReferenceExprForBorrow() && {
   if (!isExpr()) return nullptr;
 
@@ -3097,18 +3120,23 @@ class ArgEmitter {
       return;
     }
 
-    // If this is a yield, and the yield is borrowed, emit a borrowed r-value.
-    if (IsYield && param.isGuaranteed()) {
-      if (tryEmitBorrowed(std::move(arg), loweredSubstArgType,
-                          loweredSubstParamType, origParamType, paramSlice))
+    // If we have a guaranteed +0 parameter...
+    if (param.isGuaranteed()) {
+      // And this is a yield, emit a borrowed r-value.
+      if (IsYield) {
+        if (tryEmitBorrowed(std::move(arg), loweredSubstArgType,
+                            loweredSubstParamType, origParamType, paramSlice))
+          return;
+      }
+
+      if (tryEmitBorrowExpr(std::move(arg), loweredSubstArgType,
+                            loweredSubstParamType, origParamType, paramSlice))
         return;
-    }
 
-    // If we have a guaranteed paramter, see if we have a move only type and can
-    // emit it borrow.
-    //
-    // We check for move only in tryEmitBorrowedMoveOnly.
-    if (param.isGuaranteed()) {
+      // If we have a guaranteed paramter, see if we have a move only type and
+      // can emit it borrow.
+      //
+      // We check for move only in tryEmitBorrowedMoveOnly.
       if (tryEmitBorrowedMoveOnly(std::move(arg), loweredSubstArgType,
                                   loweredSubstParamType, origParamType,
                                   paramSlice))
@@ -3302,6 +3330,23 @@ class ArgEmitter {
     return true;
   }
 
+  bool tryEmitBorrowExpr(ArgumentSource &&arg, SILType loweredSubstArgType,
+                         SILType loweredSubstParamType,
+                         AbstractionPattern origParamType,
+                         ClaimedParamsRef paramsSlice) {
+    assert(paramsSlice.size() == 1);
+
+    // Try to find an expression we can emit as a borrowed l-value.
+    auto lvExpr = std::move(arg).findStorageReferenceExprForBorrowExpr(SGF);
+    if (!lvExpr)
+      return false;
+
+    emitBorrowed(lvExpr, loweredSubstArgType, loweredSubstParamType,
+                 origParamType, paramsSlice);
+
+    return true;
+  }
+
   void emitBorrowed(Expr *arg, SILType loweredSubstArgType,
                     SILType loweredSubstParamType,
                     AbstractionPattern origParamType,

lib/Sema/MiscDiagnostics.cpp

@@ -344,6 +344,11 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
         checkMoveExpr(moveExpr);
       }
 
+      // Diagnose move expression uses where the sub expression is not a declref expr
+      if (auto *borrowExpr = dyn_cast<BorrowExpr>(E)) {
+        checkBorrowExpr(borrowExpr);
+      }
+
       if (!HasReachedSemanticsProvidingExpr &&
           E == E->getSemanticsProvidingExpr()) {
         HasReachedSemanticsProvidingExpr = true;
@@ -408,6 +413,26 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
       }
     }
 
+    void checkBorrowExpr(BorrowExpr *borrowExpr) {
+      // Make sure the MoveOnly feature is set. If not, error.
+      // This should not currently be reached because the parse should ignore
+      // the _move keyword unless the feature flag is set.
+      if (!Ctx.LangOpts.hasFeature(Feature::MoveOnly)) {
+        auto error =
+          diag::experimental_moveonly_feature_can_only_be_used_when_enabled;
+        Ctx.Diags.diagnose(borrowExpr->getLoc(), error);
+      }
+
+      // Allow for a chain of member_ref exprs that end in a decl_ref expr.
+      auto *subExpr = borrowExpr->getSubExpr();
+      while (auto *memberRef = dyn_cast<MemberRefExpr>(subExpr))
+        subExpr = memberRef->getBase();
+      if (!isa<DeclRefExpr>(subExpr)) {
+        Ctx.Diags.diagnose(borrowExpr->getLoc(),
+                           diag::borrow_expression_not_passed_lvalue);
+      }
+    }
+
     static Expr *lookThroughArgument(Expr *arg) {
       while (1) {
         if (auto conv = dyn_cast<ImplicitConversionExpr>(arg))

test/SILGen/borrow_expr.swift

@@ -0,0 +1,41 @@
+// RUN: %target-swift-frontend -enable-experimental-move-only -o - -emit-silgen %s | %FileCheck %s
+
+class Klass {
+    func useKlass() {}
+}
+
+struct Struct {
+    var k = Klass()
+}
+
+func useKlass(_ k: Klass) {}
+
+// CHECK-LABEL: sil hidden [ossa] @$s11borrow_expr10simpleTestyyF : $@convention(thin) () -> () {
+// CHECK: [[ADDR:%.*]] = project_box
+//
+// First check without the borrow:
+// CHECK: [[ACCESS:%.*]] = begin_access [read] [unknown] [[ADDR]]
+// CHECK: [[GEP:%.*]] = struct_element_addr [[ACCESS]] : $*Struct, #Struct.k
+// CHECK: [[VAL:%.*]] = load [copy] [[GEP]]
+// CHECK: end_access [[ACCESS]]
+// CHECK: [[FUNC:%.*]] = function_ref @$s11borrow_expr8useKlassyyAA0D0CF : $@convention(thin) (@guaranteed Klass) -> ()
+// CHECK: apply [[FUNC]]([[VAL]])
+// CHECK: destroy_value [[VAL]]
+//
+// Now with the borrow:
+// CHECK: [[ACCESS:%.*]] = begin_access [read] [unknown] [[ADDR]]
+// CHECK: [[GEP:%.*]] = struct_element_addr [[ACCESS]] : $*Struct, #Struct.k
+// CHECK: [[VAL:%.*]] = load_borrow [[GEP]]
+// CHECK: [[FUNC:%.*]] = function_ref @$s11borrow_expr8useKlassyyAA0D0CF : $@convention(thin) (@guaranteed Klass) -> ()
+// CHECK: apply [[FUNC]]([[VAL]])
+// CHECK: end_borrow [[VAL]]
+// CHECK: end_access [[ACCESS]]
+// CHECK: } // end sil function '$s11borrow_expr10simpleTestyyF'
+func simpleTest() {
+    var s = Struct()
+    s = Struct()
+    // Without borrow.
+    useKlass(s.k)
+    // With borrow.
+    useKlass(_borrow s.k)
+}

test/Sema/borrow_expr.swift

@@ -37,3 +37,51 @@ func useApply() {
     s = S()
     (_borrow s).test()
 }
+
+func testExprFailureLet() {
+    let t = 5
+    // Next line is parsed as move(t) + t
+    let _ = _borrow t + t
+    // Next line is parsed as move(t+t)
+    let _ = _borrow (t+t) // expected-error {{'borrow' can only be applied to lvalues}}
+}
+
+func testExprFailureVar() {
+    var t = 5
+    t = 5
+    // Next line is parsed as move(t) + t
+    let _ = _borrow t + t
+    // Next line is parsed as move(t+t)
+    let _ = _borrow (t+t) // expected-error {{'borrow' can only be applied to lvalues}}
+}
+
+func letAddressOnly<T>(_ v: T) {
+    let t = v
+    let _ = _borrow t
+}
+
+struct StructWithField {
+    var k: Klass? = nil
+}
+
+func testLetStructAccessField() {
+    let t = StructWithField()
+    let _ = _borrow t.k  // expected-error {{'borrow' can only be applied to lvalues}}
+}
+
+func testVarStructAccessField() {
+    var t = StructWithField()
+    t = StructWithField()
+    let _ = _borrow t.k // expected-error {{'borrow' can only be applied to lvalues}}
+}
+
+func testLetClassAccessField() {
+    let t = Klass()
+    let _ = _borrow t.k  // expected-error {{'borrow' can only be applied to lvalues}}
+}
+
+func testVarClassAccessField() {
+    var t = Klass()
+    t = Klass()
+    let _ = _borrow t.k // expected-error {{'borrow' can only be applied to lvalues}}
+}