Reorganize trace linking and track link types.

src/lj_jit.h

@@ -174,13 +174,23 @@ typedef uint32_t ExitNo;
 typedef uint32_t TraceNo;	/* Used to pass around trace numbers. */
 typedef uint16_t TraceNo1;	/* Stored trace number. */
 
-#define TRACE_INTERP	0	/* Fallback to interpreter. */
+/* Type of link. ORDER LJ_TRLINK */
+typedef enum {
+  LJ_TRLINK_NONE,		/* Incomplete trace. No link, yet. */
+  LJ_TRLINK_ROOT,		/* Link to other root trace. */
+  LJ_TRLINK_LOOP,		/* Loop to same trace. */
+  LJ_TRLINK_TAILREC,		/* Tail-recursion. */
+  LJ_TRLINK_UPREC,		/* Up-recursion. */
+  LJ_TRLINK_DOWNREC,		/* Down-recursion. */
+  LJ_TRLINK_INTERP,		/* Fallback to interpreter. */
+  LJ_TRLINK_RETURN		/* Return to interpreter. */
+} TraceLink;
 
 /* Trace object. */
 typedef struct GCtrace {
   GCHeader;
   uint8_t topslot;	/* Top stack slot already checked to be allocated. */
-  uint8_t unused1;
+  uint8_t linktype;	/* Type of link. */
   IRRef nins;		/* Next IR instruction. Biased with REF_BIAS. */
   GCRef gclist;
   IRIns *ir;		/* IR instructions/constants. Biased with REF_BIAS. */