This fixes a regression from 592ba31. When `a` was a constant 0 and `b`
was a non-constant 0x80000000, the 32-bit negation operation would
overflow, causing an incorrect result. The sign extension needs to happen
before the negation to avoid overflow.
Note that I can't merge the SXTW and NEG into one instruction.
NEG is an alias for SUB with the first operand being set to ZR,
but "SUB (extended register)" treats register 31 as SP instead of ZR.
I've also changed the order for the case where `a` is a constant
0xFFFFFFFF. I don't think the order actually affects correctness here,
but let's use the same order for all the cases since it makes the code
easier to reason about.
This avoids a pseudo infinite loop where CodeWidget::UpdateCallstack
would lock the CPU in order to read the call stack, causing the CPU to
call Host_UpdateDisasmDialog because it's transitioning from running to
pausing, causing Host::UpdateDisasmDialog to be emitted, causing
CodeWidget::Update to be called, once again causing
CodeWidget::UpdateCallstack to be called, repeating the cycle.
Dolphin didn't go completely unresponsive during this, because
Host_UpdateDisasmDialog schedules the emitting of Host::UpdateDisasmDialog
to happen on another thread without blocking, but it was stopping certain
operations like exiting emulation from working.
This fixes a problem I was having where using frame advance with the
debugger open would frequently cause panic alerts about invalid addresses
due to the CPU thread changing MSR.DR while the host thread was trying
to access memory.
To aid in tracking down all the places where we weren't properly locking
the CPU, I've created a new type (in Core.h) that you have to pass as a
reference or pointer to functions that require running as the CPU thread.
This code doesn't need to be portable (since the goal is to have a smaller offset for x64 codegen), so if it's not supported there are other problems. Similar code exists in e.g. DSP.cpp.
While the NV extension is totally fine, the KHR extension should be able to support more hardware.
For NVIDIA, the hardware either supports both or neither, it just needs a driver from the last two years.
For AMD, the drivers from late 2022-12 seems to bring support for the KHR extension.
For Intel, the KHR is also supported for some years.
