add proper tail calls

1 files changed, 25 insertions, 8 deletions

diff --git a/vm.c b/vm.c
index 500b4bf..4a65832 100644
--- a/vm.c
+++ b/vm.c
@@ -4,6 +4,7 @@
 #include <stdbool.h>
 #include <stdio.h>
 #include <math.h>
+#include <string.h>
 
 #include "val.h"
 #include "vm.h"
@@ -174,6 +175,7 @@ int runvm(State *S) {
 		case OP_TRUE: PUSH(VAL_TRUE); break;
 		case OP_FALSE: PUSH(VAL_FALSE); break;
 
+		case OP_TAILCALL:
 		case OP_CALL: {
 			// nargs + 1 = function and args
 			uint8_t len = RBYTE();
@@ -185,14 +187,27 @@ int runvm(State *S) {
 				CHECK(nargs == func->arity, "func needs exactly %d args, but got %d",func->arity,nargs);
 
 				CHECK(th->rsp < MAXDEPTH, "rstack overflow");
-				StackFrame *sf = &th->rstack[th->rsp++];
-				sf->ip = th->ip;
-				sf->ch = th->ch;
-				sf->fp = th->fp;
-
-				th->ip = 0;
-				th->ch = &func->ch;
-				th->fp = th->sp - len;
+				if (instr != OP_TAILCALL) {
+					StackFrame *sf = &th->rstack[th->rsp++];
+					sf->ip = th->ip;
+					sf->ch = th->ch;
+					sf->fp = th->fp;
+
+					th->ip = 0;
+					th->ch = &func->ch;
+					th->fp = th->sp - len;
+				} else {
+					// xxx might invalidate open upvalues
+					memmove(&th->stack[th->fp], &th->stack[th->sp - len], len*sizeof(Val));
+					th->sp = th->fp + len;
+					th->ip = 0;
+					th->ch = &func->ch;
+
+					StackFrame *cur_sf = &th->rstack[th->rsp];
+					cur_sf->ip = th->ip;
+					cur_sf->ch = th->ch;
+					cur_sf->fp = th->fp;
+				}
 			} else if (IS_CFUNC(callee)) {
 				Val *firstarg = &th->stack[th->sp - nargs];
 				Val res = AS_CFUNC(callee)(S, nargs, firstarg);
@@ -247,6 +262,8 @@ int runvm(State *S) {
 			objarr_append(S, arr, v);
 			break;
 		}
+		default:
+			ERROR("unknown opcode");
 
 		}