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Add more planned optimizations
#Fast calls to stub functions. This is based on a trick that Nitro uses. The idea is that stub functions logically have an array parameter or several parameters, which include input jsvals and also interpreter stuff like the sp, fp, cx, etc. Much of this is constant so the call can be made fast by setting up an area in the C stack with all the arguments filled in. To make a call, we just have to store the input jsvals and do a call instruction.
#Fast paths for all common ops. For all common JSOPs, we need to inline the common cases as a fast path, and only call stub functions for slow or rare cases. This can be done incrementally, op by op. #PIC. This is really a subset of item 2. In fact, "PIC" is a bit wrong, because as Andreas pointed out, we can start by inlining fast paths that access/guard against the property cache.#Fast transition to and from traces. There are parts to this goal. First, a simpler stack layout will allow traces, Jäger, and interpreter to execute on the stack, instead of using separate stacks with copying back and forth. Second, we can use PIC-like techniques to make trace lookup fast. Third we can separate the type tags from values on the VM stack so that, when we enter trace, the required type checking reduces to a memcmp and, when we leave trace, the type restoration reduces to a memcpy.
#Eliminate PC update. In an inline-threaded interpreter, we don't need to update the PC, because EIP encodes that. To enable this, we have to make sure no ops snoop the PC. We also need to help the GC/decompiler by making sure we have some way to provide them a PC (using a mapping or something) on demand.
#Eliminate SP update. Inside basic blocks of JSOPs, we shouldn't need to keep a proper stack. Instead, we can teach the compiler to track which logical stack element is in which register and generate faster code.
#Fast closures. This is important for advanced web apps as well as Dromaeo and the V8 benchmarks. See [https://bugzilla.mozilla.org/show_bug.cgi?id=517164 bug 517164].
#Fast global variable access. We should get globals closer to being a slot access.See [https://bugzilla.mozilla.org/show_bug.cgi?id=548844 bug 548844]#Faster arguments access. fp->argv[0] should be a compile-time static offset from fp. See [https://bugzilla.mozilla.org/show_bug.cgi?id=539144 bug 539144]
