Legalize uextend and sextend to 128bit ints

cranelift/codegen/meta/src/cdsl/type_inference.rs

@@ -161,8 +161,16 @@ impl TypeEnvironment {
 
         // Check extra conditions for InTypeset constraints.
         if let Constraint::InTypeset(tv, _) = &constraint {
-            assert!(tv.base.is_none());
-            assert!(tv.name.starts_with("typeof_"));
+            assert!(
+                tv.base.is_none(),
+                "type variable is {:?}, while expecting none",
+                tv
+            );
+            assert!(
+                tv.name.starts_with("typeof_"),
+                "Name \"{}\" should start with \"typeof_\"",
+                tv.name
+            );
         }
 
         self.constraints.push(constraint);

cranelift/codegen/meta/src/shared/legalize.rs

@@ -207,6 +207,28 @@ pub(crate) fn define(insts: &InstructionGroup, imm: &Immediates) -> TransformGro
     // embedded as part of arguments), so use a custom legalization for now.
     narrow.custom_legalize(iconst, "narrow_iconst");
 
+    {
+        let inst = uextend.bind(I128).bind(I64);
+        narrow.legalize(
+            def!(a = inst(x)),
+            vec![
+                def!(ah = iconst(Literal::constant(&imm.imm64, 0))),
+                def!(a = iconcat(x, ah)),
+            ],
+        );
+    }
+
+    {
+        let inst = sextend.bind(I128).bind(I64);
+        narrow.legalize(
+            def!(a = inst(x)),
+            vec![
+                def!(ah = sshr_imm(x, Literal::constant(&imm.imm64, 63))), // splat sign bit to whole number
+                def!(a = iconcat(x, ah)),
+            ],
+        );
+    }
+
     for &bin_op in &[band, bor, bxor, band_not, bor_not, bxor_not] {
         narrow.legalize(
             def!(a = bin_op(x, y)),