cl : Command line warning D9002 : ignoring unknown option "-O3"

The warning message "cl : Command line warning D9002: ignoring unknown option '-O3'" indicates that the cl command, which is the Microsoft Visual C++ compiler, is encountering an unknown or unsupported option -O3.

The -O3 option is typically used in other compilers, such as GCC or Clang, to enable aggressive optimization levels. However, in Microsoft Visual C++, the equivalent option is /O2.

To resolve this warning and ensure compatibility with the Visual C++ compiler, replace -O3 with /O2 in your build configuration or command line.

For example, if you have a command line that looks like this:

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cl myfile.cpp -O3

Change it to:

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cl myfile.cpp /O2

By using /O2 instead of -O3, you will specify the correct optimization level for the Visual C++ compiler, and the warning message should no longer appear.