Don't GC-scan stack data redundantly.

* src/alloc.c (Fgarbage_collect): When using stack scanning, don't
redundantly scan byte-code stacks, catchlist, and handlerlist.
* src/bytecode.c (BYTE_MAINTAIN_TOP): New macros.
(struct byte_stack): Only define `top' and `bottom' if used.
(mark_byte_stack): Only define if used.
(BEFORE_POTENTIAL_GC, AFTER_POTENTIAL_GC): Nullify if BYTE_MAINTAIN_TOP
is not set.
(Fbyte_code): Don't set `bottom' unless BYTE_MAINTAIN_TOP is set.
* src/lisp.h (BYTE_MARK_STACK): New macro.
(mark_byte_stack): Only declare if BYTE_MARK_STACK is set.
* src/term.c (OUTPUT_IF): Use OUTPUT.

1 files changed, 16 insertions, 3 deletions

diff --git a/src/bytecode.c b/src/bytecode.c
index a88df080c5a..cf4a1fc225f 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -229,6 +229,8 @@ Lisp_Object Qbytecode;
 #define Bconstant 0300
 #define CONSTANTLIM 0100
 
+/* Whether to maintain a `top' and `bottom' field in the stack frame.  */
+#define BYTE_MAINTAIN_TOP (BYTE_CODE_SAFE || BYTE_MARK_STACK)
 
 /* Structure describing a value stack used during byte-code execution
    in Fbyte_code.  */
@@ -241,7 +243,9 @@ struct byte_stack
 
   /* Top and bottom of stack.  The bottom points to an area of memory
      allocated with alloca in Fbyte_code.  */
+#if BYTE_MAINTAIN_TOP
   Lisp_Object *top, *bottom;
+#endif
 
   /* The string containing the byte-code, and its current address.
      Storing this here protects it from GC because mark_byte_stack
@@ -268,6 +272,7 @@ struct byte_stack *byte_stack_list;
 
 /* Mark objects on byte_stack_list.  Called during GC.  */
 
+#if BYTE_MARK_STACK
 void
 mark_byte_stack (void)
 {
@@ -292,7 +297,7 @@ mark_byte_stack (void)
       mark_object (stack->constants);
     }
 }
-
+#endif
 
 /* Unmark objects in the stacks on byte_stack_list.  Relocate program
    counters.  Called when GC has completed.  */
@@ -346,8 +351,13 @@ unmark_byte_stack (void)
 /* Actions that must be performed before and after calling a function
    that might GC.  */
 
+#if !BYTE_MAINTAIN_TOP
+#define BEFORE_POTENTIAL_GC()   ((void)0)
+#define AFTER_POTENTIAL_GC()    ((void)0)
+#else
 #define BEFORE_POTENTIAL_GC()   stack.top = top
 #define AFTER_POTENTIAL_GC()    stack.top = NULL
+#endif
 
 /* Garbage collect if we have consed enough since the last time.
    We do this at every branch, to avoid loops that never GC.  */
@@ -447,10 +457,13 @@ If the third argument is incorrect, Emacs may crash.  */)
   stack.byte_string = bytestr;
   stack.pc = stack.byte_string_start = SDATA (bytestr);
   stack.constants = vector;
-  stack.bottom = (Lisp_Object *) alloca (XFASTINT (maxdepth)
+  top = (Lisp_Object *) alloca (XFASTINT (maxdepth)
                                          * sizeof (Lisp_Object));
-  top = stack.bottom - 1;
+#if BYTE_MAINTAIN_TOP
+  stack.bottom = top;
   stack.top = NULL;
+#endif
+  top -= 1;
   stack.next = byte_stack_list;
   byte_stack_list = &stack;