diff --git a/js/src/Makefile.in b/js/src/Makefile.in
index 4bfcdb7007e5..e1bead8a1807 100644
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -77,6 +77,36 @@ GRE_MODULE	    = 1
 
 LIBS		= $(NSPR_LIBS) 
 
+ifdef GNU_CXX
+ifdef INTEL_CXX
+# icc gets special optimize flags
+ifdef MOZ_PROFILE_GENERATE
+MODULE_OPTIMIZE_FLAGS = -O0
+else
+MODULE_OPTIMIZE_FLAGS = -O2 -ip
+endif
+else # not INTEL_CXX
+
+MODULE_OPTIMIZE_FLAGS = -O3 -fstrict-aliasing -fno-stack-protector
+
+# We normally want -fomit-frame-pointer, but we want an explicit
+# -fno-omit-frame-pointer if we're using a sampling profiler.
+ifndef MOZ_PROFILING
+MODULE_OPTIMIZE_FLAGS += -fomit-frame-pointer
+else
+MODULE_OPTIMIZE_FLAGS += -fno-omit-frame-pointer
+endif
+
+endif
+else # not GNU_CXX
+ifeq ($(OS_ARCH),SunOS)
+MODULE_OPTIMIZE_FLAGS = -xO4
+endif
+ifeq ($(OS_ARCH),WINNT)
+MODULE_OPTIMIZE_FLAGS = -O2
+endif
+endif
+
 ifeq ($(OS_ARCH),WINNT)
 NO_PROFILE_GUIDED_OPTIMIZE = 1
 endif
diff --git a/js/src/configure.in b/js/src/configure.in
index 3ef055fde5e8..dad130cfa413 100644
--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -1992,14 +1992,11 @@ case "$target" in
 *-darwin*) 
     MKSHLIB='$(CXX) $(CXXFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MKCSHLIB='$(CC) $(CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
-
-    MOZ_OPTIMIZE_FLAGS="-O3  -fstrict-aliasing -fno-stack-protector"
-    # We normally want -fomit-frame-pointer, but we want an explicit
-    # -fno-omit-frame-pointer if we're using a sampling profiler.
+    # If we're building with --enable-profiling, we need a frame pointer.
     if test -z "$MOZ_PROFILING"; then
-        MOZ_OPTIMIZE_FLAGS="$MOZ_OPTIMIZE_FLAGS -fomit-frame-pointer"
+        MOZ_OPTIMIZE_FLAGS="-O3 -fomit-frame-pointer"
     else
-        MOZ_OPTIMIZE_FLAGS="$MOZ_OPTIMIZE_FLAGS -fno-omit-frame-pointer"
+        MOZ_OPTIMIZE_FLAGS="-O3 -fno-omit-frame-pointer"
     fi
     _PEDANTIC=
     CFLAGS="$CFLAGS -fpascal-strings -fno-common"