It seems like llvm -inline pass only inlines small functions. Is there a way to inline all functions, no matter how big they are?
You can use the -inline-threshold flag to change the "cost" up to which LLVM will inline a function. A higher value means more functions will be inlined.
opt -inline -inline-threshold=10000 ...
Obviously functions can not always be inlined, particularly when the call graph contains cycles (recursive calls).