what optimization passes are done for -O4 in clang?

clang, llvm, llvm-clang

Solution

As far as I know -O4 means same thing as -O3 + enabled LTO (Link Time Optimization). See the folloing code fragments:

- Tools.cpp `// Manually translate -O to -O2 and -O4 to -O3;`

- Driver.cpp `// Check for -O4.`

Also see here:

You can produce bitcode files from clang using -emit-llvm or -flto, or the -O4 flag which is synonymous with -O3 -flto.

For optimizations used with -O3 flag see this PassManagerBuilder.cpp file (look for OptLevel variable - it will have value 3).

Problem

We are trying to implement a jit compiler whose performance is supposed to be same as doing it with clang -o4. Is there a place where I could easily get the list of optimization passes invoked by clang with -o4 is specified?

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