Tuples represented in AST already are optimized at AST level. But there are tuples created at compilation stage (see the code emitting BUILD_TUPLE). Inada's PR 4879 simplifies the peephole optimizer.

I tried to move this optimization at the compiler level, but it is more complex change. Making this change can have additional advantages, but is just more complex. I think at end all remaining peephole optimizations will be moved to the compiler, so that it will generate already optimized code. Many optimizations had already moved, and I have yet few unfinished patches.