Removes unnecessary header dependencies that have accumulated over time
as changes have been made. Lessens the amount of files that need to be
rebuilt when the headers change.
These optimizations can also apply to the 64-bit variants of the shift
opcodes; we just need to check if the instruction has an associated
pseudo-op before performing the 32-bit variant's specifics.
While we're at it, we can also relocate the code to its own function
like the rest of the cases to keep organization consistent.
We can fold division operations if:
1. The divisor is zero, then we can replace the result with zero (as this is how
ARM platforms expect it).
2. Both values are known, in which case we can just do the operation and
store the result
3. The divisor is 1, in which case just return the other operand.
It's common for an folding operation to apply to both the 32-bit and
64-bit variant of the same opcode, which leads to checking which kind of
result we need to store the value as. This moves it to its own function,
so that we don't need to duplicate it in various functions.
Multiplication operations can currently be folded if:
1. Both arguments are known constant values
2. Either operand is zero (in which case the result is also zero)
3. Either operand is one (in which case the result is the non-one
operand).
By far, one of the most common things to check for is whether or not a
value is zero, as it typically allows folding away unnecesary
operations (other close contenders that can help with eliding operations are 1 and -1).
So instead of requiring a check for an immediate and then actually
retrieving the integral value and checking it, we can wrap it within a
function to make it more convenient.
It's possible to fold cases of exclusive OR operations if they can be
known to be an identity operation, or if both operands happen to be known
immediates, in which case we can just store the result of the
exclusive-OR directly.
