ACT-Backend v1.16

Changes since v1.15, constraints:

• Checked an instruction's attribute constraints when selecting it (#283)
• Passed an instruction's address constraints to the allocator (#287)
• Read a quotient and a remainder in an attribute constraint (#289)
• Passed an address constraint's quotient and remainder to the allocator (#293)
• Read a conjunction or a bracketed condition in a constraint (#295)
• Pinned TAIDL v2.15 and TAIDL-TO v2.11 and dropped a check TAIDL now makes (#296)

This release:

• The version is 1.16 in pyproject.toml and act_backend/__init__.py, and the README's install line names v1.16. The generated crate's Cargo.toml and Cargo.lock say 1.16.0.
• generate_backend now accepts a constraint of comparisons over an instruction's attributes and integers, joined by and and or and bracketed to any depth. v1.15 refused any instruction with a constraint.
• A constraint that names no address attribute is now checked in the instruction's precondition in ir2isa_rewrites.rs. So the instruction is selected only where it holds.
• A constraint that names an address attribute, such as those set_apart and set_no_partial_overlap give, is now pushed to the allocator. So a candidate is placed only where it holds.
• Under set_apart an output is now placed apart from each marked input. Under set_no_partial_overlap it either shares each marked input's start or lies apart from it.
• A quotient and a remainder in a constraint are now rounded down as TAIDL-TO rounds them, by any divisor other than zero. That holds over the attributes and over addresses alike.
• An operand's start may now multiply two address attributes, where v1.15 refused it at generation.
• A start may now also divide or take a remainder by an attribute or by a negative integer, which v1.15 refused too. A divisor of addresses is held at 1 or more.
• An address attribute that no operand reads is now accepted.
• A comparison whose arithmetic overflows 64 bits does not hold, and fails the whole constraint where it divides. So do a division by zero and a part of an address constraint that overflows 64 bits, and the instruction is not selected.
• An address variable of a slice or a concatenate now takes its values from 0 up, as an instruction's and every offset do.
• These are still refused at generation, with the message of v1.15:
  • a constraint that holds a state variable
  • literals alone that compute to a value that overflows 64 bits
  • a quotient or a remainder of an address by zero
• A constraint with an integer literal outside the 64-bit range, or a divisor that is the literal 0, now fails as TAIDL v2.15 loads it.
• ACT-Backend now pins TAIDL v2.15, as TAIDL-TO v2.11 does. TAIDL v2.15 refuses at load an integer literal outside the signed 64-bit range and a division by the literal 0.
• The two examples compile attention.hlo to the same calls and output as in v1.15.