Make stack context saving macros equivalent to NOP, and remove the AV…

…ER which guards stack context save pre scan.

code/ss.c

@@ -54,7 +54,14 @@ Res StackScan(ScanState ss, void *stackCold,
 
   arena = ss->arena;
 
-  AVER(arena->stackWarm != NULL);
+  /* If we save stack context efficiently at all entry points to the MPS,
+    we should not need to save the stack context here, and so we should 
+    AVER(arena->stackWarm != NULL) here , to make sure that we have 
+    succeeded in writing the correct code at every entry point; However, 
+    we do not save stack context at entry points, as the performance 
+    penalty is too great. So we expect arena->stackWarm to be NULL at 
+    this point, and the stack context is saved here */
+
   warmest = arena->stackWarm;
   if (warmest == NULL) {
     /* Somehow missed saving the context at the entry point

code/ss.h

@@ -38,7 +38,11 @@ void StackHot(void **stackOut);
 
 /* STACK_CONTEXT_BEGIN -- save context */
 
-#define STACK_CONTEXT_BEGIN(arena) \
+#define STACK_CONTEXT_BEGIN(arena) STACK_CONTEXT_BEGIN_NOP
+
+#define STACK_CONTEXT_BEGIN_NOP BEGIN
+
+#define STACK_CONTEXT_BEGIN_SETJMP(arena) \
   BEGIN \
     StackContextStruct _sc; \
     STACK_CONTEXT_SAVE(&_sc); \
@@ -50,7 +54,11 @@ void StackHot(void **stackOut);
 
 /* STACK_CONTEXT_END -- clear context */
 
-#define STACK_CONTEXT_END(arena) \
+#define STACK_CONTEXT_END(arena) STACK_CONTEXT_END_NOP
+
+#define STACK_CONTEXT_END_NOP END
+
+#define STACK_CONTEXT_END_SETJMP(arena) \
     END; \
     AVER(arena->stackWarm != NULL); \
     arena->stackWarm = NULL; \