tweak tail merging logic

[sbcl.git] / src / compiler / policies.lisp

diff --git a/src/compiler/policies.lisp b/src/compiler/policies.lisp
index 18437bb..53b21e4 100644 (file)
--- a/src/compiler/policies.lisp
+++ b/src/compiler/policies.lisp
@@ -62,27 +62,18 @@ more reliable bactracing across foreign calls.")
   ("no" "maybe" "yes" "yes"))
 
 (define-optimization-quality merge-tail-calls
-    (if (or (> space debug)
-            (> speed debug))
-        3
-        0)
-  ("no" "maybe" "yes" "yes")
-  "Control whether tail-calls should reuse caller stack frame.
-Enabling this option make functions use less stack space, and make
-tail-recursive functions execute in constant stack, but debugging
-become harder, because backtraces show only part of function call
-sequence.
-
-This options has no effect when INSERT-DEBUG-CATCH is set.")
+    3
+  "Deprecated: has no effect on compiled code. (Never really did.)")
 
 (define-optimization-quality insert-debug-catch
     (if (> debug (max speed space))
         3
         0)
   ("no" "maybe" "yes" "yes")
-  "Enable possibility of returning from stack frames with the debugger.
-
-Enabling this option effectively disables MERGE-TAIL-CALLS.")
+  "Enables possibility of returning from stack frames with the debugger.
+Enabling this option causes apparent tail calls to no longer be in a tail
+position -- effectively disabling tail-merging, hence causing apparently tail
+recursive functions to no longer execute in constant stack space")
 
 (define-optimization-quality recognize-self-calls
     (if (> (max speed space) debug)