[pypy-commit] stmgc default: Change back to accessing read-markers through a non-aliasing type to allow for

[Raemi]

Author: Remi Meier <remi.meier at inf.ethz.ch>
Branch: 
Changeset: r1609:ddd64fd996c7
Date: 2015-02-06 16:13 +0100
http://bitbucket.org/pypy/stmgc/changeset/ddd64fd996c7/

Log:	Change back to accessing read-markers through a non-aliasing type to
	allow for better optimizations by the c compiler. It should be safe
	now as we do not ever rely on read markers in the signal handler any
	more (by doing an stm_validate()).

diff --git a/c8/stm/gcpage.c b/c8/stm/gcpage.c
--- a/c8/stm/gcpage.c
+++ b/c8/stm/gcpage.c
@@ -521,7 +521,8 @@
         long i;
         for (i = 1; i < NB_SEGMENTS; i++) {
             /* reset read marker */
-            *((char *)(get_segment_base(i) + (((uintptr_t)obj) >> 4))) = 0;
+            ((struct stm_read_marker_s *)
+             (get_segment_base(i) + (((uintptr_t)obj) >> 4)))->rm = 0;
         }
         return false;
     }
@@ -547,7 +548,8 @@
         long i;
         for (i = 1; i < NB_SEGMENTS; i++) {
             /* reset read marker */
-            *((char *)(get_segment_base(i) + (((uintptr_t)obj) >> 4))) = 0;
+            ((struct stm_read_marker_s *)
+             (get_segment_base(i) + (((uintptr_t)obj) >> 4)))->rm = 0;
         }
         return false;
     }
diff --git a/c8/stm/misc.c b/c8/stm/misc.c
--- a/c8/stm/misc.c
+++ b/c8/stm/misc.c
@@ -31,7 +31,8 @@
 
 bool _stm_was_read(object_t *obj)
 {
-    uint8_t rm = *((char *)(STM_SEGMENT->segment_base + (((uintptr_t)obj) >> 4)));
+    uint8_t rm = ((struct stm_read_marker_s *)
+                  (STM_SEGMENT->segment_base + (((uintptr_t)obj) >> 4)))->rm;
     assert(rm <= STM_SEGMENT->transaction_read_version);
     return rm == STM_SEGMENT->transaction_read_version;
 }
diff --git a/c8/stm/nursery.c b/c8/stm/nursery.c
--- a/c8/stm/nursery.c
+++ b/c8/stm/nursery.c
@@ -266,7 +266,8 @@
 
                 /* mark slot as unread (it can only have the read marker
                    in this segment) */
-                *((char *)(pseg->pub.segment_base + (((uintptr_t)obj) >> 4))) = 0;
+                ((struct stm_read_marker_s *)
+                 (pseg->pub.segment_base + (((uintptr_t)obj) >> 4)))->rm = 0;
 
                 _stm_large_free(stm_object_pages + item->addr);
             } TREE_LOOP_END;
diff --git a/c8/stmgc.h b/c8/stmgc.h
--- a/c8/stmgc.h
+++ b/c8/stmgc.h
@@ -24,8 +24,19 @@
 
 typedef TLPREFIX struct object_s object_t;
 typedef TLPREFIX struct stm_segment_info_s stm_segment_info_t;
+typedef TLPREFIX struct stm_read_marker_s stm_read_marker_t;
 typedef TLPREFIX char stm_char;
 
+struct stm_read_marker_s {
+    /* In every segment, every object has a corresponding read marker.
+       We assume that objects are at least 16 bytes long, and use
+       their address divided by 16.  The read marker is equal to
+       'STM_SEGMENT->transaction_read_version' if and only if the
+       object was read in the current transaction.  The nurseries
+       also have corresponding read markers, but they are never used. */
+    uint8_t rm;
+};
+
 struct stm_segment_info_s {
     uint8_t transaction_read_version;
     int segment_num;
@@ -80,7 +91,6 @@
 
 bool _stm_is_accessible_page(uintptr_t pagenum);
 
-long stm_can_move(object_t *obj);
 void _stm_test_switch(stm_thread_local_t *tl);
 void _stm_test_switch_segment(int segnum);
 void _push_obj_to_other_segments(object_t *obj);
@@ -149,7 +159,8 @@
 __attribute__((always_inline))
 static inline void stm_read(object_t *obj)
 {
-    *((stm_char *)(((uintptr_t)obj) >> 4)) = STM_SEGMENT->transaction_read_version;
+    ((stm_read_marker_t *)(((uintptr_t)obj) >> 4))->rm =
+        STM_SEGMENT->transaction_read_version;
 }
 
 __attribute__((always_inline))
@@ -226,6 +237,8 @@
 long stm_id(object_t *obj);
 void stm_set_prebuilt_identityhash(object_t *obj, long hash);
 
+long stm_can_move(object_t *obj);
+
 object_t *stm_setup_prebuilt(object_t *);
 object_t *stm_setup_prebuilt_weakref(object_t *);