+/* EXTEND_HWM_SET: note the high-water-mark to which the stack has been
+ * requested to be extended (which is likely to be less than PL_stack_max)
+ */
+#if defined DEBUGGING && !defined DEBUGGING_RE_ONLY
+# define EXTEND_HWM_SET(p, n) \
+ STMT_START { \
+ SSize_t ix = (p) - PL_stack_base + (n); \
+ if (ix > PL_curstackinfo->si_stack_hwm) \
+ PL_curstackinfo->si_stack_hwm = ix; \
+ } STMT_END
+#else
+# define EXTEND_HWM_SET(p, n) NOOP
+#endif
+
+/* _EXTEND_SAFE_N(n): private helper macro for EXTEND().
+ * Tests whether the value of n would be truncated when implicitly cast to
+ * SSize_t as an arg to stack_grow(). If so, sets it to -1 instead to
+ * trigger a panic. It will be constant folded on platforms where this
+ * can't happen.
+ */
+
+#define _EXTEND_SAFE_N(n) \
+ (sizeof(n) > sizeof(SSize_t) && ((SSize_t)(n) != (n)) ? -1 : (n))
+
+#ifdef STRESS_REALLOC
+# define EXTEND_SKIP(p, n) EXTEND_HWM_SET(p, n)
+
+# define EXTEND(p,n) STMT_START { \
+ sp = stack_grow(sp,p,_EXTEND_SAFE_N(n)); \
+ PERL_UNUSED_VAR(sp); \
+ } STMT_END
+/* Same thing, but update mark register too. */
+# define MEXTEND(p,n) STMT_START { \
+ const SSize_t markoff = mark - PL_stack_base; \
+ sp = stack_grow(sp,p,_EXTEND_SAFE_N(n)); \
+ mark = PL_stack_base + markoff; \
+ PERL_UNUSED_VAR(sp); \
+ } STMT_END
+#else
+
+/* _EXTEND_NEEDS_GROW(p,n): private helper macro for EXTEND().
+ * Tests to see whether n is too big and we need to grow the stack. Be
+ * very careful if modifying this. There are many ways to get things wrong
+ * (wrapping, truncating etc) that could cause a false negative and cause
+ * the call to stack_grow() to be skipped. On the other hand, false
+ * positives are safe.
+ * Bear in mind that sizeof(p) may be less than, equal to, or greater
+ * than sizeof(n), and while n is documented to be signed, someone might
+ * pass an unsigned value or expression. In general don't use casts to
+ * avoid warnings; instead expect the caller to fix their code.
+ * It is legal for p to be greater than PL_stack_max.
+ * If the allocated stack is already very large but current usage is
+ * small, then PL_stack_max - p might wrap round to a negative value, but
+ * this just gives a safe false positive
+ */
+
+# define _EXTEND_NEEDS_GROW(p,n) ((n) < 0 || PL_stack_max - (p) < (n))
+
+
+/* EXTEND_SKIP(): used for where you would normally call EXTEND(), but
+ * you know for sure that a previous op will have already extended the
+ * stack sufficiently. For example pp_enteriter ensures that that there
+ * is always at least 1 free slot, so pp_iter can return &PL_sv_yes/no
+ * without checking each time. Calling EXTEND_SKIP() defeats the HWM
+ * debugging mechanism which would otherwise whine
+ */
+
+# define EXTEND_SKIP(p, n) STMT_START { \
+ EXTEND_HWM_SET(p, n); \
+ assert(!_EXTEND_NEEDS_GROW(p,n)); \
+ } STMT_END
+