Prohibit spawn and sync inside statement expressions

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11564,6 +11564,8 @@ def err_cilk_spawn_invalid_func_context : Error<
   "|a varargs function}0">;
 def err_pragma_cilk_precedes_noncilk : Error<
   "expected a Cilk keyword to follow '%0'">;
+def err_cilk_in_statement_expression : Error<
+  "'%0' cannot be used inside a statement expression">;
 
 // cilk_scope
 def note_protected_by_cilk_scope: Note<

clang/lib/Sema/SemaCilk.cpp

@@ -13,6 +13,7 @@
 #include "clang/AST/ExprCilk.h"
 #include "clang/AST/StmtCilk.h"
 #include "clang/Sema/SemaInternal.h"
+#include "clang/Sema/ScopeInfo.h"
 using namespace clang;
 using namespace sema;
 
@@ -51,6 +52,15 @@ static FunctionScopeInfo *checkCilkContext(Sema &S, SourceLocation Loc,
   FunctionScopeInfo *ScopeInfo = S.getCurFunction();
   assert(ScopeInfo && "missing function scope for function");
 
+  // Cilk keywords inside statement expressions cause problems
+  // generating IR.
+  for (CompoundScopeInfo &Scope : ScopeInfo->CompoundScopes) {
+    if (Scope.IsStmtExpr) {
+      S.Diag(Loc, diag::err_cilk_in_statement_expression) << Keyword;
+      return nullptr;
+    }
+  }
+
   return ScopeInfo;
 }
 

clang/test/Cilk/stmt-expr.c

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 %s -triple x86_64-unknown-linux-gnu -fopencilk -fsyntax-only -verify
+
+extern int f(int);
+
+// CHECK_LABEL: stmt_expr_fn
+void stmt_expr_fn(int arg)
+{
+  int x = cilk_spawn(f( ({cilk_sync; 1;}) ));
+  // expected-error@-1{{'cilk_sync' cannot be used inside a statement expression}}
+  int y = ({cilk_spawn f(2); -1;});
+  // expected-error@-1{{'cilk_spawn' cannot be used inside a statement expression}}
+  int z = cilk_spawn f(3);
+}