Merge branch 'master' into v2.1

diff --cc src/lj_ffrecord.c
index 9ea81e549a86dc4b4ab1c273b8393de189e0f42f,7d83396b82806b9f5d32522b9bf316b2d15d87be..527b6c0681e69b411f77bfda26981373b234b98e
--- 1/src/lj_ffrecord.c
--- 2/src/lj_ffrecord.c
+++ b/src/lj_ffrecord.c
@@@ -778,30 -629,10 +778,30 @@@ static void LJ_FASTCALL recff_bit_tohex
  
  /* -- String library fast functions --------------------------------------- */
  
 -static void LJ_FASTCALL recff_string_len(jit_State *J, RecordFFData *rd)
 +/* Specialize to relative starting position for string. */
 +static TRef recff_string_start(jit_State *J, GCstr *s, int32_t *st, TRef tr,
 +                             TRef trlen, TRef tr0)
  {
 -  J->base[0] = emitir(IRTI(IR_FLOAD), lj_ir_tostr(J, J->base[0]), IRFL_STR_LEN);
 -  UNUSED(rd);
 +  int32_t start = *st;
 +  if (start < 0) {
 +    emitir(IRTGI(IR_LT), tr, tr0);
 +    tr = emitir(IRTI(IR_ADD), trlen, tr);
 +    start = start + (int32_t)s->len;
 +    emitir(start < 0 ? IRTGI(IR_LT) : IRTGI(IR_GE), tr, tr0);
 +    if (start < 0) {
 +      tr = tr0;
 +      start = 0;
 +    }
 +  } else if (start == 0) {
 +    emitir(IRTGI(IR_EQ), tr, tr0);
 +    tr = tr0;
 +  } else {
-     tr = emitir(IRTI(IR_ADD), tr, lj_ir_kint(J, -1));
++    tr = emitir(IRTGI(IR_ADDOV), tr, lj_ir_kint(J, -1));
 +    emitir(IRTGI(IR_GE), tr, tr0);
 +    start--;
 +  }
 +  *st = start;
 +  return tr;
  }
  
  /* Handle string.byte (rd->data = 0) and string.sub (rd->data = 1). */
@@@ -856,9 -705,9 +856,9 @@@ static void LJ_FASTCALL recff_string_ra
    if (rd->data) {  /* Return string.sub result. */
      if (end - start >= 0) {
        /* Also handle empty range here, to avoid extra traces. */
-       TRef trptr, trslen = emitir(IRTI(IR_SUB), trend, trstart);
+       TRef trptr, trslen = emitir(IRTGI(IR_SUBOV), trend, trstart);
        emitir(IRTGI(IR_GE), trslen, tr0);
 -      trptr = emitir(IRT(IR_STRREF, IRT_P32), trstr, trstart);
 +      trptr = emitir(IRT(IR_STRREF, IRT_PGC), trstr, trstart);
        J->base[0] = emitir(IRT(IR_SNEW, IRT_STR), trptr, trslen);
      } else {  /* Range underflow: return empty string. */
        emitir(IRTGI(IR_LT), trend, trstart);