wasmtime: Implement table.fill

Part of #929

crates/runtime/src/libcalls.rs

@@ -265,6 +265,41 @@ pub unsafe extern "C" fn wasmtime_table_grow(
     }
 }
 
+/// Implementation of `table.fill`.
+pub unsafe extern "C" fn wasmtime_table_fill(
+    vmctx: *mut VMContext,
+    table_index: u32,
+    dst: u32,
+    // NB: we don't know whether this is a `VMExternRef` or a pointer to a
+    // `VMCallerCheckedAnyfunc` until we look at the table's element type.
+    val: *mut u8,
+    len: u32,
+) {
+    let result = {
+        let instance = (&mut *vmctx).instance();
+        let table_index = TableIndex::from_u32(table_index);
+        let table = instance.get_table(table_index);
+        match table.element_type() {
+            TableElementType::Func => {
+                let val = val as *mut VMCallerCheckedAnyfunc;
+                table.fill(dst, val.into(), len)
+            }
+            TableElementType::Val(ty) => {
+                debug_assert_eq!(ty, crate::ref_type());
+                let val = if val.is_null() {
+                    None
+                } else {
+                    Some(VMExternRef::clone_from_raw(val))
+                };
+                table.fill(dst, val.into(), len)
+            }
+        }
+    };
+    if let Err(trap) = result {
+        raise_lib_trap(trap);
+    }
+}
+
 /// Implementation of `table.copy`.
 pub unsafe extern "C" fn wasmtime_table_copy(
     vmctx: *mut VMContext,

crates/runtime/src/table.rs

@@ -67,6 +67,26 @@ impl Table {
         }
     }
 
+    /// Fill `table[dst..dst + len]` with `val`.
+    ///
+    /// Returns a trap error on out-of-bounds accesses.
+    pub fn fill(&self, dst: u32, val: TableElement, len: u32) -> Result<(), Trap> {
+        let start = dst;
+        let end = start
+            .checked_add(len)
+            .ok_or_else(|| Trap::wasm(ir::TrapCode::TableOutOfBounds))?;
+
+        if end > self.size() {
+            return Err(Trap::wasm(ir::TrapCode::TableOutOfBounds));
+        }
+
+        for i in start..end {
+            self.set(i, val.clone()).unwrap();
+        }
+
+        Ok(())
+    }
+
     /// Grow table by the specified amount of elements.
     ///
     /// Returns the previous size of the table if growth is successful.

crates/runtime/src/vmcontext.rs

@@ -594,6 +594,10 @@ impl VMBuiltinFunctionsArray {
             wasmtime_externref_global_get as usize;
         ptrs[BuiltinFunctionIndex::externref_global_set().index() as usize] =
             wasmtime_externref_global_set as usize;
+        ptrs[BuiltinFunctionIndex::table_fill_externref().index() as usize] =
+            wasmtime_table_fill as usize;
+        ptrs[BuiltinFunctionIndex::table_fill_funcref().index() as usize] =
+            wasmtime_table_fill as usize;
 
         if cfg!(debug_assertions) {
             for i in 0..ptrs.len() {