cranelift-simplejit: add a translation mechanism for LibCalls (#747)

cranelift/module/src/backend.rs

@@ -9,6 +9,10 @@ use cranelift_codegen::isa::TargetIsa;
 use cranelift_codegen::Context;
 use cranelift_codegen::{binemit, ir};
 
+use std::borrow::ToOwned;
+use std::boxed::Box;
+use std::string::String;
+
 /// A `Backend` implements the functionality needed to support a `Module`.
 ///
 /// Two notable implementations of this trait are:
@@ -127,3 +131,22 @@ where
     /// provide additional functionality through this result.
     fn finish(self) -> Self::Product;
 }
+
+/// Default names for `ir::LibCall`s. A function by this name is imported into the object as
+/// part of the translation of a `ir::ExternalName::LibCall` variant.
+pub fn default_libcall_names() -> Box<Fn(ir::LibCall) -> String> {
+    Box::new(move |libcall| match libcall {
+        ir::LibCall::Probestack => "__cranelift_probestack".to_owned(),
+        ir::LibCall::CeilF32 => "ceilf".to_owned(),
+        ir::LibCall::CeilF64 => "ceil".to_owned(),
+        ir::LibCall::FloorF32 => "floorf".to_owned(),
+        ir::LibCall::FloorF64 => "floor".to_owned(),
+        ir::LibCall::TruncF32 => "truncf".to_owned(),
+        ir::LibCall::TruncF64 => "trunc".to_owned(),
+        ir::LibCall::NearestF32 => "nearbyintf".to_owned(),
+        ir::LibCall::NearestF64 => "nearbyint".to_owned(),
+        ir::LibCall::Memcpy => "memcpy".to_owned(),
+        ir::LibCall::Memset => "memset".to_owned(),
+        ir::LibCall::Memmove => "memmove".to_owned(),
+    })
+}