[PATCH] Consider the frame base isn't moving in calculateDbgValueHistory.

[Alexey Samsonov]

Why is RSP clobbered by the calls in the first place? If $rsp is used to address local variables, then does it mean the generated code actually has to spill $rsp before calling a function and restore $rsp after that? That looks weird.

I considered adding a liveness analysis here, but it seems that DbgValueHistoryCalculator is a wrong place for this: it's pain to match the propagation of debug variables' locations in the control flow graph with the order the actual basic blocks are emitted in the object file (as this is the order we care about when we generate .debug_loc section). It is doable, but painful and can be pretty slow. Instead, it would be better to somehow reuse/fix LiveDebugVariables pass (which is currently used only by optimized register allocator), and track locations by inserting DBG_VALUEs where necessary.

http://reviews.llvm.org/D5366