Register checks and Tracing

[One More Try]

I was thinking it might be nice to be able to track PPC register usage in the debugger, which would allow for tracing values as they jump between memory and registers.

Where would you properly do the check, would it just happen above this jit.cpp line?

if (SConfig::GetInstance().bEnableDebugging && breakpoints.IsAddressBreakPoint(op.address) &&
!CPU::IsStepping())

Also, a register changing its value would be easy to flag, but what about using/storing its value? Basically need to check if each instruction has a specific register reference, the destination register, and if it's a store instr as well.

At the very least I would add a feature to show where a register value came from for a specific break point.

[One More Try]

I figured it out. I can just do stepping like StepOut and build a list of each instruction. I used the CodeWidget UI and StepOut to test a trace.

Trace r3, display in Function Calls (bottom left). Little blurry because I resized it.:

You want to know where r3 comes from. A backtrace.
The first line says it came from r31 so then we track r31. 
We find r31 was loaded from 0x000C r1 (r1 = sp. I also saved what this address is, but don't have it listed atm). We then track the memory address to see what wrote to it earlier.
Finally, we get a hit on the tracked memory with the stw line; telling us the memory address was written here.

If you're familiar with dolphin code, you can surmise these are save/restore GPR commands. Useful for a test that jumps between memory and registers. If we used stepout from earlier in the callstack we would get more hits on where r31 came from.

It could also do forward traces, checking where a value goes and how it's used, rather than where it came from. I can make it verbose and list all uses of what is being tracked, or simply show the direct line of where something came from. I could also use this to make breakpoints like "when r3 is read/stored/loaded/changed -> break".