Add x86 SIMD average rounding

cranelift/codegen/meta/src/isa/x86/encodings.rs

@@ -1560,6 +1560,7 @@ fn define_simd(
     let formats = &shared_defs.formats;
 
     // Shorthands for instructions.
+    let avg_round = shared.by_name("avg_round");
     let bitcast = shared.by_name("bitcast");
     let bor = shared.by_name("bor");
     let bxor = shared.by_name("bxor");
@@ -1926,6 +1927,12 @@ fn define_simd(
         e.enc_32_64_maybe_isap(imul, rec_fa.opcodes(opcodes), *isap);
     }
 
+    // SIMD integer average with rounding.
+    for (ty, opcodes) in &[(I8, &PAVGB[..]), (I16, &PAVGW[..])] {
+        let avgr = avg_round.bind(vector(*ty, sse_vector_size));
+        e.enc_32_64(avgr, rec_fa.opcodes(opcodes));
+    }
+
     // SIMD logical operations
     let band = shared.by_name("band");
     let band_not = shared.by_name("band_not");

cranelift/codegen/meta/src/isa/x86/opcodes.rs

@@ -317,6 +317,12 @@ pub static PAND: [u8; 3] = [0x66, 0x0f, 0xdb];
 /// Bitwise AND NOT of xmm2/m128 and xmm1 (SSE2).
 pub static PANDN: [u8; 3] = [0x66, 0x0f, 0xdf];
 
+/// Average packed unsigned byte integers from xmm2/m128 and xmm1 with rounding (SSE2).
+pub static PAVGB: [u8; 3] = [0x66, 0x0f, 0xE0];
+
+/// Average packed unsigned word integers from xmm2/m128 and xmm1 with rounding (SSE2).
+pub static PAVGW: [u8; 3] = [0x66, 0x0f, 0xE3];
+
 /// Compare packed data for equal (SSE2).
 pub static PCMPEQB: [u8; 3] = [0x66, 0x0f, 0x74];
 

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",