Share constants between codegen and the meta crate;

cranelift/codegen/shared/src/constants.rs

@@ -0,0 +1,30 @@
+//! This module contains constants that are shared between the codegen and the meta crate, so they
+//! are kept in sync.
+
+// Numbering scheme for value types:
+//
+// 0: Void
+// 0x01-0x6f: Special types
+// 0x70-0x7d: Lane types
+// 0x7e-0x7f: Reference types
+// 0x80-0xff: Vector types
+//
+// Vector types are encoded with the lane type in the low 4 bits and log2(lanes)
+// in the high 4 bits, giving a range of 2-256 lanes.
+
+/// Start of the lane types.
+pub const LANE_BASE: u8 = 0x70;
+
+/// Base for reference types.
+pub const REFERENCE_BASE: u8 = 0x7E;
+
+/// Start of the 2-lane vector types.
+pub const VECTOR_BASE: u8 = 0x80;
+
+// Some constants about register classes and types.
+
+/// Guaranteed maximum number of top-level register classes with pressure tracking in any ISA.
+pub const MAX_TRACKED_TOP_RCS: usize = 4;
+
+/// Guaranteed maximum number of register classes in any ISA.
+pub const MAX_NUM_REG_CLASSES: usize = 32;