Bugzilla bug #39712: work around the /GT bug of MSVC 6.0 SP3.

Modified files: WIN32.mk, ntthread.c

nsprpub/config/WIN32.mk

@@ -53,14 +53,7 @@ OS_CFLAGS = -W3 -nologo -GF -Gy
 
 ifdef BUILD_OPT
 OS_CFLAGS += -MD
-# The -O2 optimization of MSVC 6.0 SP3 appears to generate
-# code that is unsafe for our use of fibers and static thread
-# local storage.  We temporarily work around this problem by
-# turning off global optimizations (-Og).
 OPTIMIZER = -O2
-ifeq ($(OS_TARGET),WINNT)
-OPTIMIZER += -Og-
-endif
 DEFINES = -UDEBUG -U_DEBUG -DNDEBUG
 DLLFLAGS = -OUT:"$@"
 OBJDIR_TAG = _OPT

nsprpub/pr/src/md/windows/ntthread.c

@@ -430,6 +430,19 @@ _PR_MD_SWITCH_CONTEXT(PRThread *thread)
     _PR_Schedule();
 }
 
+/*
+ * The /GT option of MSVC 6.0 SP3 fails to prevent compiler optimizations
+ * that are unsafe for fibers' access to static thread local storage.
+ * We work around this problem by moving all the code after the
+ * SwitchToFiber() call to a separate function.  (Bugzilla bug #39712)
+ */
+
+static void
+PostSwitchWork(void)
+{
+    POST_SWITCH_WORK();
+}
+
 void
 _PR_MD_RESTORE_CONTEXT(PRThread *thread)
 {
@@ -447,7 +460,16 @@ _PR_MD_RESTORE_CONTEXT(PRThread *thread)
         _PR_MD_SET_LAST_THREAD(me);
         thread->no_sched = 1;
         SwitchToFiber(thread->md.fiber_id);
+#if 0
         POST_SWITCH_WORK();
+#else
+        /*
+         * Move the code after SwitchToFiber() to another function so
+         * that it is not jointly optimized with the code before the
+         * SwitchToFiber() call.  See comments before PostSwitchWork().
+         */
+        PostSwitchWork();
+#endif
     }
 }