[build] Implement registers code generation in the Rust meta crate;

lib/codegen/meta/src/isa/riscv/mod.rs

@@ -0,0 +1,24 @@
+use cdsl::regs::{RegBankBuilder, RegClassBuilder};
+use isa;
+
+pub fn define() -> isa::TargetIsa {
+    let mut isa = isa::TargetIsa::new("riscv");
+
+    let builder = RegBankBuilder::new("IntRegs", "x")
+        .units(32)
+        .track_pressure(true);
+    let int_regs = isa.add_reg_bank(builder);
+
+    let builder = RegBankBuilder::new("FloatRegs", "f")
+        .units(32)
+        .track_pressure(true);
+    let float_regs = isa.add_reg_bank(builder);
+
+    let builder = RegClassBuilder::new_toplevel(&mut isa, "GPR", int_regs);
+    isa.add_reg_class(builder);
+
+    let builder = RegClassBuilder::new_toplevel(&mut isa, "FPR", float_regs);
+    isa.add_reg_class(builder);
+
+    isa
+}