It can focus on whether the stack frame is created and not yet freed before the function call
for saving saved register or passing parameters or others.

@lenary
If any arguments are passed by the stack, it is not allowed to do tail-call-opt.
Because the caller would allocate the stack for passing the arguments, and need to
free the stack after the call finished (the call must return back for free the stack).

Function with varargs passed by stack cannot be optimized to tail call.
If the varargs are all passed by registers, it can do tail call opt.

@hfinkel
Hi, I am not really sure the means of TokenFactor. I refer the implement of other target.
From document, TokenFactor is used to represent the fact that the operand operators are independent of each other.
I am not sure why other target transform all stores into one single node by using TokenFactor.
Most of target, it uses sp+offset to store arguments into stack. So the order of store instruction doesn't matter.
In AVR, it uses push instruction to store arguments. Therefore. the order of store(push) instruction can't be changed.
Could you give me some suggestion? Thanks.

LGTM.

Add test case for large stack offset.

Remove unused fixme comment in test/CodeGen/X86/loop-search.ll.

Remove unnecessary checking in test/CodeGen/WebAssembly/cfg-stackify.ll.

Update test cases.