How to compile with o2 and ob1

[freiza]

How to set compiler flags. I want to compile my application with
/ob1 and /o2 switches in qt creator. Where should I specify these flags?

[ChrisW67]

In the PRO file QMAKE_CFLAGS and/or QMAKE_CXXFLAGS and their related variables.

However, you will find that /O2 is the default for a MSVC release build anyway. Setting /Ob1 defeats some of the tools used by /O2.

[freiza]

I am using mingw.
I wrote it like this but not working.
QMAKE_CSSFLAGS += -O2 \
-Ob1

and this is also not working
QMAKE_CSSFLAGS += /O2 \
/Ob1

[wysota]

CXXFLAGS and not CSSFLAGS.