gccrs: Add HIR to GCC GENERIC lowering entry point

This patch contains the entry point and utilities used for the lowering
of HIR nodes to `tree`s. It also contains a constant evaluator, ported
over from the C++ frontend.

	gcc/rust/
	* backend/rust-compile-context.cc: New.
	* backend/rust-compile-context.h: New.
	* backend/rust-compile.cc: New.
	* backend/rust-compile.h: New.
	* backend/rust-constexpr.cc: New.
	* backend/rust-constexpr.h: New.

Co-authored-by: David Faust <david.faust@oracle.com>
Co-authored-by: Faisal Abbas <90.abbasfaisal@gmail.com>
Signed-off-by: Faisal Abbas <90.abbasfaisal@gmail.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/gcc/rust/backend/rust-constexpr.h b/gcc/rust/backend/rust-constexpr.h
new file mode 100644
index 0000000..3cfcec8
--- /dev/null
+++ b/gcc/rust/backend/rust-constexpr.h
@@ -0,0 +1,31 @@
+// This file is part of GCC.
+
+// GCC is free software; you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3, or (at your option) any later
+// version.
+
+// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+// for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with GCC; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#ifndef RUST_CONSTEXPR
+#define RUST_CONSTEXPR
+
+#include "rust-system.h"
+#include "tree.h"
+
+namespace Rust {
+namespace Compile {
+
+extern tree fold_expr (tree);
+
+} // namespace Compile
+} // namespace Rust
+
+#endif // RUST_CONSTEXPR