Add x86 SIMD average rounding

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

@@ -548,6 +548,32 @@ fn define_simd_arithmetic(
         .operands_in(vec![x, y])
         .operands_out(vec![a]),
     );
+
+    let IxN = &TypeVar::new(
+        "IxN",
+        "A SIMD vector type containing integers",
+        TypeSetBuilder::new()
+            .ints(Interval::All)
+            .simd_lanes(Interval::All)
+            .includes_scalars(false)
+            .build(),
+    );
+
+    let a = &Operand::new("a", IxN);
+    let x = &Operand::new("x", IxN);
+    let y = &Operand::new("y", IxN);
+
+    ig.push(
+        Inst::new(
+            "avg_round",
+            r#"
+        Unsigned average with rounding: `a := (x + y + 1) // 2`
+        "#,
+            &formats.binary,
+        )
+        .operands_in(vec![x, y])
+        .operands_out(vec![a]),
+    );
 }
 
 #[allow(clippy::many_single_char_names)]
@@ -627,7 +653,6 @@ pub(crate) fn define(
             .includes_scalars(false)
             .build(),
     );
-
     let Any = &TypeVar::new(
         "Any",
         "Any integer, float, boolean, or reference scalar or vector type",