Wasm: Add support for typed select instruction

Reference types introduces a typed select operation. It has identical execution
semantics so no codegen change is needed.

cranelift/wasm/src/code_translator.rs

@@ -132,6 +132,13 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
             let (arg1, arg2, cond) = state.pop3();
             state.push1(builder.ins().select(cond, arg1, arg2));
         }
+        Operator::TypedSelect { ty: _ } => {
+            // We ignore the explicit type parameter as it is only needed for
+            // validation, which we require to have been performed before
+            // translation.
+            let (arg1, arg2, cond) = state.pop3();
+            state.push1(builder.ins().select(cond, arg1, arg2));
+        }
         Operator::Nop => {
             // We do nothing
         }
@@ -968,9 +975,6 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
         Operator::F32Le | Operator::F64Le => {
             translate_fcmp(FloatCC::LessThanOrEqual, builder, state)
         }
-        Operator::TypedSelect { .. } => {
-            return Err(wasm_unsupported!("proposed typed select operator {:?}", op))
-        }
         Operator::RefNull => state.push1(builder.ins().null(environ.reference_type())),
         Operator::RefIsNull => {
             let arg = state.pop1();

cranelift/wasmtests/select.wat

@@ -0,0 +1,19 @@
+(module
+  (func $untyped-select (result i32)
+  	i32.const 42
+  	i32.const 24
+  	i32.const 1
+  	select)
+
+  (func $typed-select-1 (result anyref)
+  	ref.null
+  	ref.null
+  	i32.const 1
+  	select (result anyref))
+
+  (func $typed-select-2 (param anyref) (result anyref)
+    ref.null
+    local.get 0
+    i32.const 1
+    select (result anyref))
+)