add riscv64 backend for cranelift. (#4271)

Add a RISC-V 64 (`riscv64`, RV64GC) backend.

Co-authored-by: yuyang <756445638@qq.com>
Co-authored-by: Chris Fallin <chris@cfallin.org>
Co-authored-by: Afonso Bordado <afonsobordado@az8.co>

cranelift/codegen/meta/src/isa/mod.rs

@@ -4,6 +4,7 @@ use crate::shared::Definitions as SharedDefinitions;
 use std::fmt;
 
 mod arm64;
+mod riscv64;
 mod s390x;
 pub(crate) mod x86;
 
@@ -13,6 +14,7 @@ pub enum Isa {
     X86,
     Arm64,
     S390x,
+    Riscv64,
 }
 
 impl Isa {
@@ -30,13 +32,14 @@ impl Isa {
             "aarch64" => Some(Isa::Arm64),
             "s390x" => Some(Isa::S390x),
             x if ["x86_64", "i386", "i586", "i686"].contains(&x) => Some(Isa::X86),
+            "riscv64" | "riscv64gc" | "riscv64imac" => Some(Isa::Riscv64),
             _ => None,
         }
     }
 
     /// Returns all supported isa targets.
     pub fn all() -> &'static [Isa] {
-        &[Isa::X86, Isa::Arm64, Isa::S390x]
+        &[Isa::X86, Isa::Arm64, Isa::S390x, Isa::Riscv64]
     }
 }
 
@@ -47,6 +50,7 @@ impl fmt::Display for Isa {
             Isa::X86 => write!(f, "x86"),
             Isa::Arm64 => write!(f, "arm64"),
             Isa::S390x => write!(f, "s390x"),
+            Isa::Riscv64 => write!(f, "riscv64"),
         }
     }
 }
@@ -57,6 +61,7 @@ pub(crate) fn define(isas: &[Isa], shared_defs: &mut SharedDefinitions) -> Vec<T
             Isa::X86 => x86::define(shared_defs),
             Isa::Arm64 => arm64::define(shared_defs),
             Isa::S390x => s390x::define(shared_defs),
+            Isa::Riscv64 => riscv64::define(shared_defs),
         })
         .collect()
 }

cranelift/codegen/meta/src/isa/riscv64.rs

@@ -0,0 +1,27 @@
+use crate::cdsl::isa::TargetIsa;
+use crate::cdsl::settings::{SettingGroup, SettingGroupBuilder};
+
+use crate::shared::Definitions as SharedDefinitions;
+
+fn define_settings(_shared: &SettingGroup) -> SettingGroup {
+    let mut setting = SettingGroupBuilder::new("riscv64");
+
+    let _has_m = setting.add_bool("has_m", "has extension M?", "", false);
+    let _has_a = setting.add_bool("has_a", "has extension A?", "", false);
+    let _has_f = setting.add_bool("has_f", "has extension F?", "", false);
+    let _has_d = setting.add_bool("has_d", "has extension D?", "", false);
+    let _has_v = setting.add_bool("has_v", "has extension V?", "", false);
+    let _has_b = setting.add_bool("has_b", "has extension B?", "", false);
+    let _has_c = setting.add_bool("has_c", "has extension C?", "", false);
+    let _has_zbkb = setting.add_bool("has_zbkb", "has extension zbkb?", "", false);
+
+    let _has_zicsr = setting.add_bool("has_zicsr", "has extension zicsr?", "", false);
+    let _has_zifencei = setting.add_bool("has_zifencei", "has extension zifencei?", "", false);
+
+    setting.build()
+}
+
+pub(crate) fn define(shared_defs: &mut SharedDefinitions) -> TargetIsa {
+    let settings = define_settings(&shared_defs.settings);
+    TargetIsa::new("riscv64", settings)
+}