Where can I find the sequence of optimizations used by clang according to -OX?
clang executes the precisely same sequence of passes as opt -ON. So, you can do something like
llvm-as < /dev/null | opt -O3 -disable-output -debug-pass=Arguments
to derive the "full" set of passes which are run at O3.
来源：https://stackoverflow.com/questions/7796151/where-to-find-the-optimization-sequence-for-clang-ox