Do not always use checked arithmetic

[sirasistant]

Problem

Checked arithmetic has extra cost, both in constrained and unconstrained. We could both offer the user unchecked arithmetic blocks similarly to solidity, and have compiler issued operations like loop counter arithmetic be unchecked.

Happy Case

• SSA operations can be checked or unchecked so we can issue unchecked operations where we know no overflow is possible (loops, for example)
• Users can write unchecked {} blocks to denote which arithmetic operations don't need overflow checks. These will issue unchecked SSA ops.

Unchecked operations in Brillig can use native arithmetic saving on bytecode size and execution cost. Unchecked operations in ACIR can be cheaper by chaining operations without truncating until we need to truncate to avoid overflowing the field.

Workaround

None

Workaround Description

No response

Additional Context

No response

Project Impact

None

Blocker Context

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response

[Savio-Sou]

Unchecked<{integer}> could be a potential happy case as well

[olehmisar]

i would prefer .unchecked_{add,sub,mul,div} or .wrapping_{add,sub,mul,div}, whichever name is more appropriate.