Nonmoving: Ensure write barrier vanishes in non-threaded RTS

3 files changed, 26 insertions, 6 deletions

diff --git a/includes/Cmm.h b/includes/Cmm.h
index 42aa0bf550..546e81e8f6 100644
--- a/includes/Cmm.h
+++ b/includes/Cmm.h
@@ -950,19 +950,23 @@
     return (dst);
 
 
+//
+// Nonmoving write barrier helpers
+//
+// See Note [Update remembered set] in NonMovingMark.c.
+
 #if defined(THREADED_RTS)
-#define IF_WRITE_BARRIER_ENABLED                               \
+#define IF_NONMOVING_WRITE_BARRIER_ENABLED                     \
     if (W_[nonmoving_write_barrier_enabled] != 0) (likely: False)
 #else
 // A similar measure is also taken in rts/NonMoving.h, but that isn't visible from C--
-#define IF_WRITE_BARRIER_ENABLED                               \
+#define IF_NONMOVING_WRITE_BARRIER_ENABLED                     \
     if (0)
 #define nonmoving_write_barrier_enabled 0
 #endif
 
 // A useful helper for pushing a pointer to the update remembered set.
-// See Note [Update remembered set] in NonMovingMark.c.
 #define updateRemembSetPushPtr(p)                                    \
-    IF_WRITE_BARRIER_ENABLED {                                       \
+    IF_NONMOVING_WRITE_BARRIER_ENABLED {                             \
       ccall updateRemembSetPushClosure_(BaseReg "ptr", p "ptr");     \
     }
diff --git a/includes/Stg.h b/includes/Stg.h
index 73de97055f..8f0abdbf6d 100644
--- a/includes/Stg.h
+++ b/includes/Stg.h
@@ -597,3 +597,21 @@ typedef union {
   c;                                            \
 })
 #endif
+
+/* -----------------------------------------------------------------------------
+   Nonmoving GC write barrier
+   -------------------------------------------------------------------------- */
+
+// Note that RTS code should not condition on this directly by rather
+// use the IF_NONMOVING_WRITE_BARRIER_ENABLED macro to ensure that
+// the barrier is eliminated in the non-threaded RTS.
+extern StgWord DLL_IMPORT_DATA_VAR(nonmoving_write_barrier_enabled);
+
+// A similar macro is defined in includes/Cmm.h for C-- code.
+#if defined(THREADED_RTS)
+#define IF_NONMOVING_WRITE_BARRIER_ENABLED \
+    if (RTS_UNLIKELY(nonmoving_write_barrier_enabled))
+#else
+#define IF_NONMOVING_WRITE_BARRIER_ENABLED \
+    if (0)
+#endif
diff --git a/includes/rts/NonMoving.h b/includes/rts/NonMoving.h
index 6a6d96b2c8..f64769e8a9 100644
--- a/includes/rts/NonMoving.h
+++ b/includes/rts/NonMoving.h
@@ -20,5 +20,3 @@ void updateRemembSetPushClosure_(StgRegTable *reg, StgClosure *p);
 void updateRemembSetPushClosure(Capability *cap, StgClosure *p);
 
 void updateRemembSetPushThunk_(StgRegTable *reg, StgThunk *p);
-
-extern StgWord DLL_IMPORT_DATA_VAR(nonmoving_write_barrier_enabled);