WIP: rewrite C++ backend to be CHEADmaster

+ C allows for a bit more control, and we can manually handle closure
  contexts. For example `examples/fib.fwd` now works for effectively any
  `n`, pretty cool.

+ Fairly slow Fibonacci, I must admit. Initial profiling indicates it's
  mainly due to branch mispredictions, but I'll have to look into this a
  bit deeper.

+ The code is a bit hacked together, for now I'm more interested in
  getting things working, I'll worry about making things pretty later.

+ For testing, there's also initial support for modules, just so I can
  print stuff to the terminal

+ This commit is way too big, lol

1 files changed, 66 insertions, 0 deletions

diff --git a/lib/fwd.h b/lib/fwd.h
new file mode 100644
index 0000000..54d75a2
--- /dev/null
+++ b/lib/fwd.h
@@ -0,0 +1,66 @@
+#ifndef FWD_H
+#define FWD_H
+
+#include <fwd/mod.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#ifndef FWD_FRAME_SIZE
+#error "no frame size defined, internal compiler error"
+#endif
+
+/* should probably add some compiler checks but good enough for now */
+#define FWD_MUSTTAIL [[clang::musttail]]
+
+typedef void *fwd_stack_t;
+typedef void *fwd_args_t;
+typedef fwd_stack_t (*fwd_call_t)(fwd_stack_t, fwd_args_t);
+
+typedef struct {
+	fwd_call_t call;
+	fwd_args_t args;
+} fwd_closure_t;
+
+typedef struct {} fwd_start_t;
+
+static inline fwd_stack_t create_fwd_stack()
+{
+	return NULL;
+}
+
+static inline void *fwd_stack_alloc(fwd_stack_t *top)
+{
+	if (*top) {
+		fwd_stack_t *prev = *top;
+		*top = *prev;
+		return prev + 1;
+	}
+
+	fwd_stack_t *new = malloc(FWD_FRAME_SIZE + sizeof(fwd_stack_t));
+	*new = NULL;
+	return new + 1;
+}
+
+static inline void fwd_stack_free(fwd_stack_t *stack, void *loc)
+{
+	fwd_stack_t *freed = (fwd_stack_t *)loc - 1;
+	*freed = *stack;
+	*stack = freed;
+}
+
+static inline void destroy_fwd_stack(fwd_stack_t *stack)
+{
+	fwd_stack_t *prev = *stack;
+	while (prev) {
+		fwd_stack_t *cur = prev;
+		prev = *cur;
+		free(cur);
+	}
+}
+
+#define FWD_CONTAINER_OF(ptr, type, member) \
+	(type *)((char *)(ptr) - offsetof(type, member))
+
+#endif /* FWD_H */