8e9e9c52a1
The ISLE language's lexer previously used a very primitive `i64::from_str_radix` call to parse integer constants, allowing values in the range -2^63..2^63 only. Also, underscores to separate digits (as is allwoed in Rust) were not supported. Finally, 128-bit constants were not supported at all. This PR addresses all issues above: - Integer constants are internally stored as 128-bit values. - Parsing supports either signed (-2^127..2^127) or unsigned (0..2^128) range. Negation works independently of that, so one can write `-0xffff..ffff` (128 bits wide, i.e., -(2^128-1)) to get a `1`. - Underscores are supported to separate groups of digits, so one can write `0xffff_ffff`. - A minor oversight was fixed: hex constants can start with `0X` (uppercase) as well as `0x`, for consistency with Rust and C. This PR also adds a new kind of ISLE test that actually runs a driver linked to compiled ISLE code; we previously didn't have any such tests, but it is now quite useful to assert correct interpretation of constant values.
ISLE: Instruction Selection / Lowering Expressions
ISLE is a domain specific language (DSL) for instruction selection and lowering
clif instructions to vcode's MachInsts in Cranelift.
ISLE is a statically-typed term-rewriting language. You define rewriting rules
that map input terms (clif instructions) into output terms (MachInsts). These
rules get compiled down into Rust source test that uses a tree of match
expressions that is as good or better than what you would have written by hand.