[CodeGenFunction] Fix emission of implicit syncs before returns for r…

…eturn statements processed early in a function.

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -394,7 +394,8 @@ void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
 
     PopCleanupBlocks(PrologueCleanupDepth, {}, CompilingCilk);
     SyncEmitted = true;
-  } else if (CompilingCilk && Builder.GetInsertBlock()) {
+  } else if (CompilingCilk && Builder.GetInsertBlock() &&
+             ReturnBlock.getBlock()->use_empty()) {
     // If we're compiling Cilk, emit an implicit sync for the function.
     EmitImplicitSyncCleanup();
     SyncEmitted = true;

clang/test/Cilk/early-return-while.c

@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 %s -triple x86_64-unknown-linux-gnu -fcilkplus -verify -ftapir=none -S -emit-llvm -o - | FileCheck %s
+// expected-no-diagnostics
+
+void bar();
+int baz(int);
+
+void foo(int p) {
+  while (p) {
+    if (baz(p))
+      return;
+    _Cilk_spawn bar();
+    --p;
+  }
+  bar();
+}
+
+// CHECK-LABEL: define {{.*}}void @foo(
+
+// CHECK: br i1 %{{.+}}, label %[[WHILE_BODY:.+]], label %[[WHILE_END:.+]]
+
+// CHECK: [[WHILE_BODY]]:
+// CHECK: br i1 %{{.+}}, label %[[THEN:.+]], label %[[END:.+]]
+
+// CHECK: [[THEN]]:
+// CHECK-NEXT: br label %[[RETURN:.+]]
+
+// CHECK: detach within %[[SYNCREG:.+]], label %[[DETACHED:.+]], label %[[CONTINUE:.+]]
+
+// CHECK: [[DETACHED]]:
+// CHECK: call void {{.*}}@bar()
+// CHECK: reattach within %[[SYNCREG]], label %[[CONTINUE]]
+
+// CHECK: [[CONTINUE]]:
+// CHECK: br
+
+// CHECK: [[WHILE_END]]:
+// CHECK-NEXT: call void {{.*}}@bar()
+// CHECK-NEXT: br label %[[RETURN]]
+
+// CHECK: [[RETURN]]:
+// CHECK-NEXT: sync within %[[SYNCREG]]
+
+// CHECK: ret void

clang/test/Cilk/early-return.c

@@ -25,7 +25,8 @@ void foo(int p) {
 
 // CHECK: [[END]]:
 // CHECK-NEXT: call void {{.*}}@bar()
-// CHECK-NEXT: sync within %[[SYNCREG]]
+
+// CHECK: sync within %[[SYNCREG]]
 
 // CHECK: ret void