Index: tools/v8_gypfiles/toolchain.gypi
--- tools/v8_gypfiles/toolchain.gypi.orig
+++ tools/v8_gypfiles/toolchain.gypi
@@ -861,11 +861,9 @@
               # Don't use -O3 with sanitizers.
               ['asan==0 and msan==0 and lsan==0 \
                 and tsan==0 and ubsan==0 and ubsan_vptr==0', {
-                'cflags': ['-O3'],
-                'cflags!': ['-O2'],
+                'cflags': ['-O2'],
               }, {
                 'cflags': ['-O2'],
-                'cflags!': ['-O3'],
               }],
             ],
           }],