[COMMITTED,3/3] Allow the static chain to be set from C

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 839111a..95b6b1b 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -453,6 +453,8 @@  const struct c_common_resword c_common_reswords[] =
   { "__attribute__",	RID_ATTRIBUTE,	0 },
   { "__auto_type",	RID_AUTO_TYPE,	D_CONLY },
   { "__bases",          RID_BASES, D_CXXONLY },
+  { "__builtin_call_with_static_chain",
+    RID_BUILTIN_CALL_WITH_STATIC_CHAIN, D_CONLY },
   { "__builtin_choose_expr", RID_CHOOSE_EXPR, D_CONLY },
   { "__builtin_complex", RID_BUILTIN_COMPLEX, D_CONLY },
   { "__builtin_shuffle", RID_BUILTIN_SHUFFLE, 0 },
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index ca6fc8b..7e53923 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -101,7 +101,7 @@  enum rid
   RID_EXTENSION, RID_IMAGPART, RID_REALPART, RID_LABEL,      RID_CHOOSE_EXPR,
   RID_TYPES_COMPATIBLE_P,      RID_BUILTIN_COMPLEX,	     RID_BUILTIN_SHUFFLE,
   RID_DFLOAT32, RID_DFLOAT64, RID_DFLOAT128,
-  RID_FRACT, RID_ACCUM, RID_AUTO_TYPE,
+  RID_FRACT, RID_ACCUM, RID_AUTO_TYPE, RID_BUILTIN_CALL_WITH_STATIC_CHAIN,
 
   /* C11 */
   RID_ALIGNAS, RID_GENERIC,
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index f90f6af..8a4fd39 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -7414,6 +7414,46 @@  c_parser_postfix_expression (c_parser *parser)
 	      = comptypes (e1, e2) ? integer_one_node : integer_zero_node;
 	  }
 	  break;
+	case RID_BUILTIN_CALL_WITH_STATIC_CHAIN:
+	  {
+	    vec<c_expr_t, va_gc> *cexpr_list;
+	    c_expr_t *e2_p;
+	    tree chain_value;
+
+	    c_parser_consume_token (parser);
+	    if (!c_parser_get_builtin_args (parser,
+					    "__builtin_call_with_static_chain",
+					    &cexpr_list, false))
+	      {
+		expr.value = error_mark_node;
+		break;
+	      }
+	    if (vec_safe_length (cexpr_list) != 2)
+	      {
+		error_at (loc, "wrong number of arguments to "
+			       "%<__builtin_call_with_static_chain%>");
+		expr.value = error_mark_node;
+		break;
+	      }
+
+	    expr = (*cexpr_list)[0];
+	    e2_p = &(*cexpr_list)[1];
+	    *e2_p = convert_lvalue_to_rvalue (loc, *e2_p, true, true);
+	    chain_value = e2_p->value;
+	    mark_exp_read (chain_value);
+
+	    if (TREE_CODE (expr.value) != CALL_EXPR)
+	      error_at (loc, "first argument to "
+			"%<__builtin_call_with_static_chain%> "
+			"must be a call expression");
+	    else if (TREE_CODE (TREE_TYPE (chain_value)) != POINTER_TYPE)
+	      error_at (loc, "second argument to "
+			"%<__builtin_call_with_static_chain%> "
+			"must be a pointer type");
+	    else
+	      CALL_EXPR_STATIC_CHAIN (expr.value) = chain_value;
+	    break;
+	  }
 	case RID_BUILTIN_COMPLEX:
 	  {
 	    vec<c_expr_t, va_gc> *cexpr_list;
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index d10a815..7178c9a 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -8913,6 +8913,7 @@  in the Cilk Plus language manual which can be found at
 @node Other Builtins
 @section Other Built-in Functions Provided by GCC
 @cindex built-in functions
+@findex __builtin_call_with_static_chain
 @findex __builtin_fpclassify
 @findex __builtin_isfinite
 @findex __builtin_isnormal
@@ -9501,6 +9502,18 @@  depending on the arguments' types.  For example:
 
 @end deftypefn
 
+@deftypefn {Built-in Function} @var{type} __builtin_call_with_static_chain (@var{call_exp}, @var{pointer_exp})
+
+The @var{call_exp} expression must be a function call, and the
+@var{pointer_exp} expression must be a pointer.  The @var{pointer_exp}
+is passed to the function call in the target's static chain location.
+The result of builtin is the result of the function call.
+
+@emph{Note:} This builtin is only available for C@.
+This builtin can be used to call Go closures from C.
+
+@end deftypefn
+
 @deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2})
 
 You can use the built-in function @code{__builtin_choose_expr} to
diff --git a/gcc/testsuite/gcc.dg/cwsc0.c b/gcc/testsuite/gcc.dg/cwsc0.c
new file mode 100644
index 0000000..3d92222
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cwsc0.c
@@ -0,0 +1,16 @@ 
+/* { dg-do compile } */
+
+#include <stddef.h>
+
+void foo(void);
+void test(int (*f)(void), char *p)
+{
+  __builtin_call_with_static_chain(f(), p);
+  __builtin_call_with_static_chain(p, f());  /* { dg-error "must be a call" } */
+  __builtin_call_with_static_chain(f() + 1, p); /* { dg-error "must be a call" } */
+  __builtin_call_with_static_chain(f(), 0);  /* { dg-error "must be a pointer" } */
+  __builtin_call_with_static_chain(f(), NULL);
+  __builtin_call_with_static_chain(foo, p);  /* { dg-error "must be a call" } */
+  __builtin_call_with_static_chain(foo(), p);
+  __builtin_call_with_static_chain(foo(), foo);
+}
diff --git a/gcc/testsuite/gcc.dg/cwsc1.c b/gcc/testsuite/gcc.dg/cwsc1.c
new file mode 100644
index 0000000..e793e26
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cwsc1.c
@@ -0,0 +1,46 @@ 
+/* { dg-do run } */
+/* { dg-options "-O" } */
+
+#if defined(__x86_64__)
+# define CHAIN	"%r10"
+#elif defined(__i386__)
+# define CHAIN  "%ecx"
+#elif defined(__aarch64__)
+# define CHAIN  "x18"
+#elif defined(__alpha__)
+# define CHAIN  "$1"
+#elif defined(__arm__)
+# define CHAIN  "ip"
+#elif defined(__powerpc__)
+# define CHAIN  "11"
+#elif defined(__s390__)
+# define CHAIN  "%r0"
+#elif defined(__sparc__)
+# ifdef __arch64__
+#  define CHAIN "%g5"
+# else
+#  define CHAIN "%g2"
+# endif
+#endif
+
+#ifdef CHAIN
+void *__attribute__((noinline, noclone)) foo(void)
+{
+  register void *chain __asm__(CHAIN);
+  return chain;
+}
+
+void * (*ptr)(void) = foo;
+extern void abort(void);
+
+int main()
+{
+  char c;
+  void *x = __builtin_call_with_static_chain(ptr(), &c);
+  if (x != &c)
+    abort();
+  return 0;
+}
+#else
+int main() { return 0; }
+#endif