diff --git a/C/absmi.c b/C/absmi.c
index 807f55968..5033081ee 100644
--- a/C/absmi.c
+++ b/C/absmi.c
@@ -1544,7 +1544,7 @@ Yap_absmi(int inp)
       }
 #endif
       PREG = NEXTOP(PREG, L);
-      GONext();
+      JMPNext();
       ENDBOp();
 
       /* copy database term               */
@@ -1618,7 +1618,7 @@ Yap_absmi(int inp)
 #ifdef DEPTH_LIMIT
       DEPTH = YREG[E_DEPTH];
 #endif
-      GONext();
+      JMPNext();
       ENDBOp();
 
 
@@ -1670,7 +1670,7 @@ Yap_absmi(int inp)
 #ifdef DEPTH_LIMIT
       DEPTH = YREG[E_DEPTH];
 #endif
-      GONext();
+      JMPNext();
       ENDBOp();
 
 
@@ -2023,7 +2023,7 @@ Yap_absmi(int inp)
 #endif	/* LOW_LEVEL_TRACER */
 #ifdef FROZEN_STACKS
 #ifdef YAPOR_SBA
-	  if (pt0 < TR_FZ || pt0 > CurrentTrailTop)
+	  if (pt0 < TR_FZ || pt0 > CurrentTrailTop+MinTrailGap)
 #else
 	  if (pt0 < TR_FZ)
 #endif /* YAPOR_SBA */
@@ -2073,7 +2073,7 @@ Yap_absmi(int inp)
 #ifdef YAPOR_SBA
 		(ADDR) pt1 >= HeapTop
 #else
-		IN_BETWEEN(LOCAL_TrailBase, pt1, CurrentTrailTop)
+		IN_BETWEEN(LOCAL_TrailBase, pt1, CurrentTrailTop+MinTrailGap)
 #endif /* YAPOR_SBA */
 		)
             {
@@ -2646,7 +2646,7 @@ Yap_absmi(int inp)
 	      !(LOCAL_ActiveSignals & ~YAP_CREEP_SIGNAL))  ||
 	    (PREG->opc != Yap_opcode(_procceed) &&
 	     PREG->opc != Yap_opcode(_cut_e))) {
-	  GONext();
+	  JMPNext();
 	}  
 	PP = PREVOP(PREG,p)->u.p.p;
 	ASP = YREG+E_CB;
@@ -7902,7 +7902,7 @@ Yap_absmi(int inp)
 	}
 #endif
       }
-      GONext();
+      JMPNext();
       ENDBOp();
 
       BOp(try_logical, OtaLl);
@@ -8559,7 +8559,7 @@ Yap_absmi(int inp)
         }
 
       PREG = NEXTOP(PREG, aFlp);
-      GONext();
+      JMPNext();
       
       ENDBOp();
 
diff --git a/C/exec.c b/C/exec.c
index 9c0b37695..8b4d3ddc5 100644
--- a/C/exec.c
+++ b/C/exec.c
@@ -1630,7 +1630,7 @@ Yap_InitYaamRegs(void)
   H = H0 = ((CELL *) LOCAL_GlobalBase)+ Yap_AttsSize/sizeof(CELL);
   RESET_VARIABLE(H0-1);
   LCL0 = ASP = (CELL *) LOCAL_LocalBase;
-  CurrentTrailTop = (tr_fr_ptr)LOCAL_TrailTop;
+  CurrentTrailTop = (tr_fr_ptr)(LOCAL_TrailTop-MinTrailGap);
   /* notice that an initial choice-point and environment
    *must* be created since for the garbage collector to work */
   B = NULL;
diff --git a/C/grow.c b/C/grow.c
index 71ebb5c45..72642470c 100644
--- a/C/grow.c
+++ b/C/grow.c
@@ -125,7 +125,7 @@ SetHeapRegs(int copying_threads USES_REGS)
   /* Adjust stack addresses */
   LOCAL_TrailBase = TrailAddrAdjust(LOCAL_TrailBase);
   LOCAL_TrailTop = TrailAddrAdjust(LOCAL_TrailTop);
-  CurrentTrailTop = (tr_fr_ptr)LOCAL_TrailTop;
+  CurrentTrailTop = (tr_fr_ptr)(LOCAL_TrailTop-MinTrailGap);
   if (LOCAL_GDiff) {
     /* make sure we are not just expanding the delay stack */
     LOCAL_GlobalBase = BaseAddrAdjust(LOCAL_GlobalBase);
@@ -1851,7 +1851,7 @@ Yap_CopyThreadStacks(int worker_q, int worker_p, int incremental)
   LOCAL_LocalBase = REMOTE_LocalBase(worker_p);
   LOCAL_TrailBase = REMOTE_TrailBase(worker_p);
   LOCAL_TrailTop = REMOTE_TrailTop(worker_p);
-  CurrentTrailTop = (tr_fr_ptr)LOCAL_TrailTop;
+  CurrentTrailTop = (tr_fr_ptr)(LOCAL_TrailTop-MinTrailGap);
   size = REMOTE_ThreadHandle(worker_q).stack_address-REMOTE_ThreadHandle(worker_p).stack_address;
   LOCAL_TrDiff = LOCAL_LDiff = LOCAL_GDiff = LOCAL_GDiff0 = LOCAL_DelayDiff = LOCAL_BaseDiff = size;
   LOCAL_XDiff = LOCAL_HDiff = 0;
diff --git a/H/Regs.h b/H/Regs.h
index 849f01512..782cde3d3 100644
--- a/H/Regs.h
+++ b/H/Regs.h
@@ -37,7 +37,7 @@
 #endif
 
 #ifdef __x86_64__
-#undef  PUSH_REGS
+#define  PUSH_REGS 1
 #undef  PUSH_X
 #endif
 
diff --git a/H/absmi.h b/H/absmi.h
index 9ac2b4163..0bf239e22 100644
--- a/H/absmi.h
+++ b/H/absmi.h
@@ -96,13 +96,12 @@ register struct yami* P1REG asm ("bp"); /* can't use yamop before Yap.h */
 #ifdef BP_FREE
 #undef BP_FREE
 #endif
-#define SHADOW_REGS    1
 #define SHADOW_S       1
 //#define SHADOW_Y       1
 #define S_IN_MEM       1
 #define      Y_IN_MEM  1
 #define     TR_IN_MEM  1
-#define USE_PREFETCH   1
+#define LIMITED_PREFETCH   1
 #endif /* __x86_64__ */
 
 #else /* other compilers */
@@ -361,7 +360,7 @@ restore_absmi_regs(REGSTORE * old_regs)
 
 #define DO_PREFETCH_W(TYPE) to_go = (void *)(NEXTOP(PREG,TYPE)->u.o.opcw)
 
-#if LIMITED_PREFETCH
+#if LIMITED_PREFETCH||USE_PREFETCH
 
 #define ALWAYS_START_PREFETCH(TYPE) \
  { register void *to_go; DO_PREFETCH(TYPE)
@@ -448,7 +447,7 @@ restore_absmi_regs(REGSTORE * old_regs)
 #define JMPNextW()						\
 	JMP((void *)(PREG->u.o.opcw))
 
-#if USE_THREADED_CODE && LIMITED_PREFETCH
+#if USE_THREADED_CODE && (LIMITED_PREFETCH || USE_PREFETCH)
 
 #define ALWAYS_GONext() JMP(to_go)
 
@@ -682,10 +681,10 @@ Macros to check the limits of stacks
 
 #else
 
-#define check_trail(x) if (Unsigned(CurrentTrailTop) - Unsigned(x) < MinTrailGap) \
+#define check_trail(x) if (Unsigned(CurrentTrailTop) > Unsigned(x)) \
 			goto notrailleft
 
-#define check_trail_in_indexing(x) if (Unsigned(CurrentTrailTop) - Unsigned(x) < MinTrailGap) \
+#define check_trail_in_indexing(x) if (Unsigned(CurrentTrailTop) < Unsigned(x)) \
 			goto notrailleft_from_index
 
 #endif
@@ -725,7 +724,7 @@ Macros to check the limits of stacks
 #define store_at_least_one_arg(arity)                             \
                  BEGP(pt0);                                       \
 		 pt0 = XREGS+(arity);                             \
-                 do { register CELL x = pt0[0];                   \
+                 do { CELL x = pt0[0];                   \
                      S_YREG = (S_YREG)-1;			          \
                      --pt0;                                       \
                      (S_YREG)[0] = x;	                          \