# CMP0138

Added in version 3.24.

`CheckIPOSupported` uses flags from calling project.

The `CheckIPOSupported` module `check_ipo_supported()` command compiles a test project to determine whether the toolchain supports `INTERPROCEDURAL_OPTIMIZATION`. CMake 3.23 and below run the check with the default values of the `CMAKE_<LANG>_FLAGS` and `CMAKE_<LANG>_FLAGS_<CONFIG>` variables for the current environment and toolchain settings. However, some projects may modify these flag variables to add flags that affect availability of the toolchain's IPO features. CMake 3.24 and above prefer to honor the calling project's values for these variables. This policy provides compatibility for projects that have not been updated to expect this behavior.

The `OLD` behavior for this policy is to ignore the calling project's values of `CMAKE_<LANG>_FLAGS` and `CMAKE_<LANG>_FLAGS_<CONFIG>`. The `NEW` behavior for this policy is to use the values of those variables as compiler flags in the test project.

This policy was introduced in CMake version 3.24. It may be set by `cmake_policy()` or `cmake_minimum_required()`. If it is not set, CMake does not warn, and uses `OLD` behavior.

Note

The `OLD` behavior of a policy is `deprecated by definition` and may be removed in a future version of CMake.