Summary

The current recipe for parmetis allows conflicting optimization levels to appear on the compile line in a way that isn't expected. For example: spack -d install parmetis%gcc cflags="-O3 -march=native" doesn't compile with the expected CFLAGS. I expect to see compile lines similar to this:

/usr/bin/gcc -O3 -march=native <include directives and defines> -o file.o -c file.c

Actual Result

/usr/bin/gcc -O3 -march=native <include directives and defines> -O2 -g -DNDEBUG -o file.o -c file.c

Because -O2 is listed after -O3 the optimization is not what I expect. I believe the -O2 -g -DNDEBUG flags are inserted by CMake as they are the default CMAKE_C_FLAGS_RELWITHDEBINFO values for gcc.

Possible solution

If SPACK_CFLAGS is set in the build environment, then zero-out the cmake defaulted CMAKE_C_FLAGS_XXX variables. #6839 demonstrates this model for metis and #6860 demonstrates this for parmetis, but I think it should be included in CMakePackage (possibly via the flag_handler function).

Related Issues

#6640
#6749
#6839
#6860