[m-rev.] diff: more LLDS accurate GC tweaks

[Fergus Henderson]

Estimated hours taken: 1
Branches: main

runtime/mercury_accurate_gc.c:
	Add some XXX comments.
	Fix a bug where the checking for `type != MR_LONG_LVAL_TYPE_STACKVAR'
	was being done in the wrong place.

Workspace: /home/ceres/fjh/mercury
Index: runtime/mercury_accurate_gc.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_accurate_gc.c,v
retrieving revision 1.26
diff -u -d -r1.26 mercury_accurate_gc.c
--- runtime/mercury_accurate_gc.c	22 Oct 2003 08:50:15 -0000	1.26
+++ runtime/mercury_accurate_gc.c	23 Oct 2003 06:33:29 -0000
@@ -373,6 +373,10 @@
 		/*
 		** Save the old succip and its location.
 		*/
+		/*
+		** XXX The code below is wrong for temp frames,
+		**     which do not have the succip or succfr slots!
+		*/
 		assert(location == -1); /* succip is saved in succip_slot */
 		saved_success_location = MR_succip_slot_addr(curfr_at_signal);
 		saved_success = *saved_success_location;
@@ -550,6 +554,7 @@
 	** This should be OK, because none of the values used by a procedure
 	** will be stored in registers across a call, since we have no
 	** caller-save registers (they are all callee-save).
+	** XXX except for the topmost frame!
 	*/
         type_params = MR_materialize_type_params_base(label_layout,
             NULL, stack_pointer, current_frame);
@@ -598,17 +603,21 @@
 		int                     number;
 
 		location = proc_layout->MR_sle_succip_locn;
-		type = MR_LONG_LVAL_TYPE(location);
-		number = MR_LONG_LVAL_NUMBER(location);
-		if (type != MR_LONG_LVAL_TYPE_STACKVAR) {
-			MR_fatal_error("can only handle stackvars");
-		}
 		if (MR_DETISM_DET_STACK(proc_layout->MR_sle_detism)) {
+			type = MR_LONG_LVAL_TYPE(location);
+			number = MR_LONG_LVAL_NUMBER(location);
+			if (type != MR_LONG_LVAL_TYPE_STACKVAR) {
+				MR_fatal_error("can only handle stackvars");
+			}
 			success_ip = (MR_Code *)
 				MR_based_stackvar(stack_pointer, number);
 			stack_pointer = stack_pointer - 
 				proc_layout->MR_sle_stack_slots;
 		} else {
+			/*
+			** XXX The code below is wrong for temp frames,
+			**     which do not have the succip or succfr slots!
+			*/
 			/* succip is saved in succip_slot */
 			assert(location == -1);
 			success_ip = MR_succip_slot(current_frame);
@@ -687,7 +696,9 @@
 		** saved; This should be OK, because none of the values used
 		** by a procedure will be stored in registers across a call,
 		** since we have no caller-save registers (they are all
-		** callee-save).
+		** callee-save).  XXX except for frame which was active
+		** when we entered the garbage collector!
+		**
 		** XXX Is it right to pass MR_redofr_slot(max_frame) here?
 		**     Why not just max_frame?
 		*/

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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