diff --git a/js/src/Makefile.in b/js/src/Makefile.in
index 0fb86c3bc760..3c5f60d8f945 100644
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -442,8 +442,6 @@ ifeq ($(TARGET_CPU),sparc)
 ifdef GNU_CC
 CFLAGS   += -mcpu=v9
 CXXFLAGS += -mcpu=v9
-else
-ASFLAGS  += -xarch=v8plus -P -L -D_ASM -D__STDC__=0 -K PIC
 endif # GNU_CC
 
 endif
@@ -460,17 +458,25 @@ LDFLAGS += -ljemalloc
 endif
 endif
 
+ifdef SOLARIS_SUNPRO_CXX
 # Sun Studio x86 has an optimization bug with LIR.cpp, use -xO2 instead.
-ifeq ($(OS_ARCH),SunOS)
 ifeq (86,$(findstring 86,$(OS_TEST)))
-ifndef GNU_CC
 LIR.o: LIR.cpp Makefile.in
 	$(REPORT_BUILD)
 	@$(MAKE_DEPS_AUTO_CXX)
 	$(CXX) -o $@ -c $(patsubst -xO%,-xO2,$(COMPILE_CFLAGS)) $<
-endif
-endif
-endif
+else
+# Sun Studio SPARC doesn't work well with gcc inline asm, use lock_SunOS_sparc*.il
+jslock.o: jslock.cpp Makefile.in lock_sparcv8plus.il lock_sparcv9.il
+	$(REPORT_BUILD)
+	@$(MAKE_DEPS_AUTO_CXX)
+ifeq (sparcv9,$(findstring sparcv9,$(OS_TEST)))
+	$(CXX) -o $@ -c $(COMPILE_CFLAGS) $(srcdir)/lock_sparcv9.il $<
+else
+	$(CXX) -o $@ -c $(COMPILE_CFLAGS) $(srcdir)/lock_sparcv8plus.il $<
+endif # sparcv9
+endif # x86
+endif # SOLARIS_SUNPRO_CXX
 
 # Allow building jsinterp.c with special optimization flags
 ifdef INTERP_OPTIMIZER
diff --git a/js/src/jslock.cpp b/js/src/jslock.cpp
index fda95263c8ad..ff216adad3e0 100644
--- a/js/src/jslock.cpp
+++ b/js/src/jslock.cpp
@@ -151,7 +151,8 @@ NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
     return (int)res;
 }
 
-#elif defined(__sparc) && (defined(__GNUC__) || defined(__SUNPRO_CC))
+#elif defined(__sparc)
+#if defined(__GNUC__)
 
 static JS_ALWAYS_INLINE int
 NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
@@ -171,6 +172,14 @@ NativeCompareAndSwap(jsword *w, jsword ov, jsword nv)
     return (int)res;
 }
 
+#elif defined(__SUNPRO_CC)
+
+/* Implementation in lock_sparc*.il */
+extern "C" int
+NativeCompareAndSwap(jsword *w, jsword ov, jsword nv);
+
+#endif
+
 #elif defined(AIX)
 
 #include <sys/atomic_op.h>
diff --git a/js/src/lock_sparcv8plus.il b/js/src/lock_sparcv8plus.il
new file mode 100644
index 000000000000..e7b55d5f6ec4
--- /dev/null
+++ b/js/src/lock_sparcv8plus.il
@@ -0,0 +1,84 @@
+! 
+! ***** BEGIN LICENSE BLOCK *****
+! Version: MPL 1.1/GPL 2.0/LGPL 2.1
+!
+! The contents of this file are subject to the Mozilla Public License Version
+! 1.1 (the "License"); you may not use this file except in compliance with
+! the License. You may obtain a copy of the License at
+! http://www.mozilla.org/MPL/
+!
+! Software distributed under the License is distributed on an "AS IS" basis,
+! WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+! for the specific language governing rights and limitations under the
+! License.
+!
+! The Original Code is Mozilla Communicator client code, released
+! March 31, 1998.
+!
+! The Initial Developer of the Original Code is
+! Netscape Communications Corporation.
+! Portions created by the Initial Developer are Copyright (C) 1998-1999
+! the Initial Developer. All Rights Reserved.
+!
+! Contributor(s):
+!
+! Alternatively, the contents of this file may be used under the terms of
+! either the GNU General Public License Version 2 or later (the "GPL"), or
+! the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+! in which case the provisions of the GPL or the LGPL are applicable instead
+! of those above. If you wish to allow use of your version of this file only
+! under the terms of either the GPL or the LGPL, and not to allow others to
+! use your version of this file under the terms of the MPL, indicate your
+! decision by deleting the provisions above and replace them with the notice
+! and other provisions required by the GPL or the LGPL. If you do not delete
+! the provisions above, a recipient may use your version of this file under
+! the terms of any one of the MPL, the GPL or the LGPL.
+!
+! ***** END LICENSE BLOCK *****
+
+!
+!  atomic compare-and-swap routines for V8+ (ultrasparc)
+!
+!  ======================================================================
+!
+!  Perform the sequence *a = b atomically with respect to previous value
+!  of a (a0). If *a==a0 then assign *a to b, all in one atomic operation.
+!  Returns 1 if assignment happened, and 0 otherwise.	
+!
+!  usage : old_val = compare_and_swap(address, oldval, newval)
+!
+!  -----------------------
+!  Note on REGISTER USAGE:
+!  as this is a LEAF procedure, a new stack frame is not created;
+!  we use the caller stack frame so what would normally be %i (input)
+!  registers are actually %o (output registers).  Also, we must not
+!  overwrite the contents of %l (local) registers as they are not
+!  assumed to be volatile during calls.
+!
+!  So, the registers used are:
+!     %o0  [input]   - the address of the value to increment
+!     %o1  [input]   - the old value to compare with	
+!     %o2  [input]   - the new value to set for [%o0]
+!     %o3  [local]   - work register
+!  -----------------------
+!  ======================================================================
+!
+!  v8plus
+
+    .inline NativeCompareAndSwap,3
+
+	stbar
+	cas [%o0],%o1,%o2               ! compare *w with old value and set to new if equal
+	cmp %o1,%o2                     ! did we succeed?
+	be,a 1f                         ! yes
+	mov 1,%o0                       ! return true (annulled when no jump)
+	mov 0,%o0                       ! return false
+1:
+
+    .end
+
+!
+!  end
+!
+!  ======================================================================
+!
diff --git a/js/src/lock_sparcv9.il b/js/src/lock_sparcv9.il
new file mode 100644
index 000000000000..e87e065d76eb
--- /dev/null
+++ b/js/src/lock_sparcv9.il
@@ -0,0 +1,84 @@
+! 
+! ***** BEGIN LICENSE BLOCK *****
+! Version: MPL 1.1/GPL 2.0/LGPL 2.1
+!
+! The contents of this file are subject to the Mozilla Public License Version
+! 1.1 (the "License"); you may not use this file except in compliance with
+! the License. You may obtain a copy of the License at
+! http://www.mozilla.org/MPL/
+!
+! Software distributed under the License is distributed on an "AS IS" basis,
+! WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+! for the specific language governing rights and limitations under the
+! License.
+!
+! The Original Code is Mozilla Communicator client code, released
+! March 31, 1998.
+!
+! The Initial Developer of the Original Code is
+! Netscape Communications Corporation.
+! Portions created by the Initial Developer are Copyright (C) 1998-1999
+! the Initial Developer. All Rights Reserved.
+!
+! Contributor(s):
+!
+! Alternatively, the contents of this file may be used under the terms of
+! either the GNU General Public License Version 2 or later (the "GPL"), or
+! the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+! in which case the provisions of the GPL or the LGPL are applicable instead
+! of those above. If you wish to allow use of your version of this file only
+! under the terms of either the GPL or the LGPL, and not to allow others to
+! use your version of this file under the terms of the MPL, indicate your
+! decision by deleting the provisions above and replace them with the notice
+! and other provisions required by the GPL or the LGPL. If you do not delete
+! the provisions above, a recipient may use your version of this file under
+! the terms of any one of the MPL, the GPL or the LGPL.
+!
+! ***** END LICENSE BLOCK *****
+
+!
+!  atomic compare-and-swap routines for V9 (ultrasparc)
+!
+!  ======================================================================
+!
+!  Perform the sequence *a = b atomically with respect to previous value
+!  of a (a0). If *a==a0 then assign *a to b, all in one atomic operation.
+!  Returns 1 if assignment happened, and 0 otherwise.	
+!
+!  usage : old_val = compare_and_swap(address, oldval, newval)
+!
+!  -----------------------
+!  Note on REGISTER USAGE:
+!  as this is a LEAF procedure, a new stack frame is not created;
+!  we use the caller stack frame so what would normally be %i (input)
+!  registers are actually %o (output registers).  Also, we must not
+!  overwrite the contents of %l (local) registers as they are not
+!  assumed to be volatile during calls.
+!
+!  So, the registers used are:
+!     %o0  [input]   - the address of the value to increment
+!     %o1  [input]   - the old value to compare with	
+!     %o2  [input]   - the new value to set for [%o0]
+!     %o3  [local]   - work register
+!  -----------------------
+!  ======================================================================
+!
+!  v9
+
+    .inline NativeCompareAndSwap,3
+
+	stbar
+	casx [%o0],%o1,%o2              ! compare *w with old value and set to new if equal
+	cmp %o1,%o2                     ! did we succeed?
+	be,a 1f                         ! yes
+	mov 1,%o0                       ! return true (annulled when no jump)
+	mov 0,%o0                       ! return false
+1:
+
+    .end
+
+!
+!  end
+!
+!  ======================================================================
+!