Go patch committed: Don't crash on f(g()) if g returns a zero-sized value

[Ian Lance Taylor via Gcc-patches]

This patch to the GCC interface of the Go frontend fixes a crash in
f(g()) if g returns a zero-sized value.  In that case the GCC
interface modifies g to return void, since GCC's middle-end does not
have solid support for zero-sized values.  This patch detects the
f(g()) case and replaces the call to g() with (g(), zero).  The test
case for this is https://go.dev/cl/417481.  This fixes
https://go.dev/issue/23868.  Bootstrapped and ran Go testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

* go-gcc.cc (Gcc_backend::call_expression): Handle a void
argument, as for f(g()) where g returns a zero-sized type.

1eb1495f7d0fa9b49f6f3c34bbbf4dd1e850607c
diff --git a/gcc/go/go-gcc.cc b/gcc/go/go-gcc.cc
index f3de7a8c183..7b4b2adb058 100644
--- a/gcc/go/go-gcc.cc
+++ b/gcc/go/go-gcc.cc
@@ -2112,6 +2112,19 @@ Gcc_backend::call_expression(Bfunction*, // containing 
fcn for call
       args[i] = fn_args.at(i)->get_tree();
       if (args[i] == error_mark_node)
         return this->error_expression();
+      if (TREE_TYPE(args[i]) == void_type_node)
+       {
+         // This can happen for a case like f(g()) where g returns a
+         // zero-sized type, because in that case we've changed g to
+         // return void.
+         tree t = TYPE_ARG_TYPES(TREE_TYPE(TREE_TYPE(fn)));
+         for (size_t j = 0; j < i; ++j)
+           t = TREE_CHAIN(t);
+         tree arg_type = TREE_TYPE(TREE_VALUE(t));
+         args[i] = fold_build2_loc(EXPR_LOCATION(args[i]), COMPOUND_EXPR,
+                                   arg_type, args[i],
+                                   build_zero_cst(arg_type));
+       }
     }
 
   tree fndecl = fn;