Verify support for -enforce-exclusivity=checked.

Fix a verifier assert and add a test case for begin/end access markers.

Author: atrick

lib/SIL/SILVerifier.cpp

@@ -1263,7 +1263,8 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
             isa<ProjectBoxInst>(op) ||
             isa<RefElementAddrInst>(op) ||
             isa<SILFunctionArgument>(op) ||
-            isa<BeginAccessInst>(op),
+            isa<BeginAccessInst>(op) ||
+            isa<MarkUninitializedInst>(op),
             "begin_access operand must be a root address derivation");
 
     if (BAI->getModule().getStage() != SILStage::Raw) {

test/SILGen/access_marker_gen.swift

@@ -0,0 +1,58 @@
+// RUN: %target-swift-frontend -parse-as-library -Xllvm -sil-full-demangle -enforce-exclusivity=checked -emit-silgen %s | %FileCheck %s
+
+public struct S {
+  var i: Int
+  var o: AnyObject?
+}
+
+// CHECK-LABEL: sil hidden [noinline] @_T017access_marker_gen5initSAA1SVs9AnyObject_pSgF : $@convention(thin) (@owned Optional<AnyObject>) -> @owned S {
+// CHECK: bb0(%0 : $Optional<AnyObject>):
+// CHECK: %[[BOX:.*]] = alloc_box ${ var S }, var, name "s"
+// CHECK: %[[ADDRS:.*]] = project_box %[[BOX]] : ${ var S }, 0
+// CHECK: %[[UNINIT:.*]] = mark_uninitialized [var] %[[ADDRS]] : $*S
+// CHECK: cond_br %{{.*}}, bb1, bb2
+// CHECK: bb1:
+// CHECK: %[[ACCESS1:.*]] = begin_access [modify] [unknown] %[[UNINIT]] : $*S
+// CHECK: assign %{{.*}} to %[[ACCESS1]] : $*S
+// CHECK: end_access %[[ACCESS1]] : $*S
+// CHECK: bb2:
+// CHECK: %[[ACCESS2:.*]] = begin_access [modify] [unknown] %[[UNINIT]] : $*S
+// CHECK: assign %{{.*}} to %[[ACCESS2]] : $*S
+// CHECK: end_access %[[ACCESS2]] : $*S
+// CHECK: bb3:
+// CHECK: %[[ACCESS3:.*]] = begin_access [read] [unknown] %[[UNINIT]] : $*S
+// CHECK: %[[RET:.*]] = load [copy] %[[ACCESS3]] : $*S
+// CHECK: end_access %[[ACCESS3]] : $*S
+// CHECK: return %[[RET]] : $S
+// CHECK-LABEL: } // end sil function '_T017access_marker_gen5initSAA1SVs9AnyObject_pSgF'
+@inline(never)
+func initS(_ o: AnyObject?) -> S {
+  var s: S
+  if o == nil {
+    s = S(i: 0, o: nil)
+  } else {
+    s = S(i: 1, o: o)
+  }
+  return s
+}
+
+@inline(never)
+func takeS(_ s: S) {}
+
+// CHECK-LABEL: sil @_T017access_marker_gen14modifyAndReadSyyF : $@convention(thin) () -> () {
+// CHECK: bb0:
+// CHECK: %[[BOX:.*]] = alloc_box ${ var S }, var, name "s"
+// CHECK: %[[ADDRS:.*]] = project_box %[[BOX]] : ${ var S }, 0
+// CHECK: %[[ACCESS1:.*]] = begin_access [modify] [unknown] %[[ADDRS]] : $*S
+// CHECK: %[[ADDRI:.*]] = struct_element_addr %15 : $*S, #S.i
+// CHECK: assign %{{.*}} to %[[ADDRI]] : $*Int
+// CHECK: end_access %[[ACCESS1]] : $*S
+// CHECK: %[[ACCESS2:.*]] = begin_access [read] [unknown] %[[ADDRS]] : $*S
+// CHECK: %{{.*}} = load [copy] %[[ACCESS2]] : $*S
+// CHECK: end_access %[[ACCESS2]] : $*S
+// CHECK-LABEL: } // end sil function '_T017access_marker_gen14modifyAndReadSyyF'
+public func modifyAndReadS() {
+  var s = initS(nil)
+  s.i = 42
+  takeS(s)
+}