tl;dr: I want to control which optimization and transformation can and will run on my code. Does Clang/LLVM permit such an approach?
I am doing this with GCC. But at first, it seems for some reason GCC does not allow optimizations to run unless I am passing -Ox flag (x>=1). The approach I thought would work is using -O3 and disabling all the optimizations one by one with -fno-XXX, then passing each optimization I want with -fXXX. Even after doing that it seems GCC does take the flags seriously. Sometimes it might consider the -fXXX flags, but sometimes it totally ignores.
I was investigating this issue more recently due to a project I am involved in. I realized that there are two sets of optimizations and transformation can happen in Clang/LLVM. Clang can do a few optimizations itself on AST and then LLVM will run its own optimizations. Please correct me if I am wrong.
Here is a list of few questions I am trying to find an answer for:
- I am looking for a list of optimizations that Clang might do. Where can I find them?
- I am looking for a list of optimizations that LLVM might do. Where can I find them?
- Is there any way to disable/enable specific Clang optimization?
- Is there any way to disable/enable specific LLVM optimization?
- Would LLVM/Clang respect specific optimization flags?
I appreciate immensely any help regarding these questions.