Function inlining is a big source of suboptimal sequences. Even if your codegen for a function is perfect up front, as soon as it is inlined into some other per

Function inlining is a big source of suboptimal sequences. Even if your codegen for a function is perfect up front, as soon as it is inlined into some other perfect code the combination tends to be decidedly non-perfect, and hence fed into CSE and so forth. Plus unless you can persuade programmers to write perfectly efficient functions in the first place you need that optimiser to produce the initially perfect codegen.