Add 'consts' to executor stack frame

This leads to slightly faster lookups because the constants base does not
need to be looked up from the current function.  Code footprint is also
decreased by around 0.5kB which is nice.

src/duk_js_executor.c

@@ -1943,10 +1943,10 @@ DUK_LOCAL void duk__executor_handle_debugger(duk_hthread *thr, duk_activation *a
  */
 
 #define DUK__STRICT()       (DUK_HOBJECT_HAS_STRICT(&(fun)->obj))
-#define DUK__REG(x)         (thr->valstack_bottom[(x)])
-#define DUK__REGP(x)        (&thr->valstack_bottom[(x)])
-#define DUK__CONST(x)       (DUK_HCOMPILEDFUNCTION_GET_CONSTS_BASE(thr->heap, fun)[(x)])
-#define DUK__CONSTP(x)      (&DUK_HCOMPILEDFUNCTION_GET_CONSTS_BASE(thr->heap, fun)[(x)])
+#define DUK__REG(x)         (*(thr->valstack_bottom + (x)))
+#define DUK__REGP(x)        (thr->valstack_bottom + (x))
+#define DUK__CONST(x)       (*(consts + (x)))
+#define DUK__CONSTP(x)      (consts + (x))
 #define DUK__REGCONST(x)    ((x) < DUK_BC_REGLIMIT ? DUK__REG((x)) : DUK__CONST((x) - DUK_BC_REGLIMIT))
 #define DUK__REGCONSTP(x)   ((x) < DUK_BC_REGLIMIT ? DUK__REGP((x)) : DUK__CONSTP((x) - DUK_BC_REGLIMIT))
 
@@ -1973,7 +1973,7 @@ DUK_INTERNAL void duk_js_execute_bytecode(duk_hthread *exec_thr) {
 	/* "hot" variables for interpretation -- not volatile, value not guaranteed in setjmp error handling */
 	duk_hthread *thr;             /* stable */
 	duk_hcompiledfunction *fun;   /* stable */
-	/* 'consts' is computed on-the-fly */
+	duk_tval *consts;             /* stable */
 	/* 'funcs' is quite rarely used, so no local for it */
 
 	/* "hot" temps for interpretation -- not volatile, value not guaranteed in setjmp error handling */
@@ -2138,6 +2138,8 @@ DUK_INTERNAL void duk_js_execute_bytecode(duk_hthread *exec_thr) {
 		fun = (duk_hcompiledfunction *) DUK_ACT_GET_FUNC(act);
 		DUK_ASSERT(fun != NULL);
 		DUK_ASSERT(thr->valstack_top - thr->valstack_bottom == fun->nregs);
+		consts = DUK_HCOMPILEDFUNCTION_GET_CONSTS_BASE(thr->heap, fun);
+		DUK_ASSERT(consts != NULL);
 	}
 
 #if defined(DUK_USE_DEBUGGER_SUPPORT)