Add prepare_for_function_redefine

cranelift/simplejit/Cargo.toml

@@ -14,6 +14,7 @@ cranelift-module = { path = "../module", version = "0.68.0" }
 cranelift-native = { path = "../native", version = "0.68.0" }
 cranelift-codegen = { path = "../codegen", version = "0.68.0", default-features = false, features = ["std"] }
 cranelift-entity = { path = "../entity", version = "0.68.0" }
+anyhow = "1.0"
 region = "2.2.0"
 libc = { version = "0.2.42" }
 errno = "0.2.4"

cranelift/simplejit/src/backend.rs

@@ -393,6 +393,28 @@ impl SimpleJITModule {
             data_objects_to_finalize: Vec::new(),
         }
     }
+
+    /// Allow a single future `define_function` on a previously defined function. This allows for
+    /// hot code swapping and lazy compilation of functions.
+    pub fn prepare_for_function_redefine(&mut self, func_id: FuncId) -> ModuleResult<()> {
+        let decl = self.declarations.get_function_decl(func_id);
+        if !decl.linkage.is_definable() {
+            return Err(ModuleError::InvalidImportDefinition(decl.name.clone()));
+        }
+
+        if self.compiled_functions[func_id].is_none() {
+            return Err(ModuleError::Backend(anyhow::anyhow!(
+                "Tried to redefine not yet defined function {}",
+                decl.name
+            )));
+        }
+
+        self.compiled_functions[func_id] = None;
+
+        // FIXME return some kind of handle that allows for deallocating the function
+
+        Ok(())
+    }
 }
 
 impl<'simple_jit_backend> Module for SimpleJITModule {