how to use different gcc versions and optimization parameters

[hargrove]

I am new to phoronix test suite. I have two questions and maybe the two questions are same. Firstly, My gcc version is 5.4, I want to compare gcc5.4 with gcc7.2 . I want to know how to reproduce a result like "http://openbenchmarking.org/result/1710310-AL-GCC72VSGC26". After I execute "phoronix-test-suite benchmark hpcg", the result is about gcc5.4. How can I get a comparison gcc5.4 and gcc7.2? Do I need to install gcc7.2 in my laptop at first?
Secondly, how should I use different gcc optimization paremeters, for example, "-O1", "-O2",..., getting a result like "https://www.phoronix.com/scan.php?page=article&item=clang-gcc-opts&num=2"?
Thanks in advance.

[Michael]

You need to first install the compilers on the system and then update the PATH or point cc to the correct compiler, etc. Likewise, CFLAGS / CXXFLAGS for compiler flags.

[hargrove]

Thank you for your reply and helps. You are right, and I indeed need to install alternative compiler. Now I can compare results of different compilers and optimization parameters by setting CFLAGS and CXXFLAGS. The post "https://www.phoronix.com/forums/forum/phoronix/phoronix-test-suite/855314-change-compiler-and-compilation-flag-automatically" is helpful. I am now studying other features about phoronix-test-suite. Thanks a lot.