Add operand kind and format for unsigned 128-bit immediates

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

@@ -5,6 +5,7 @@ pub fn define(immediates: &OperandKinds, entities: &OperandKinds) -> FormatRegis
     // Shorthands for immediates.
     let uimm8 = immediates.by_name("uimm8");
     let uimm32 = immediates.by_name("uimm32");
+    let uimm128 = immediates.by_name("uimm128");
     let imm64 = immediates.by_name("imm64");
     let ieee32 = immediates.by_name("ieee32");
     let ieee64 = immediates.by_name("ieee64");
@@ -30,6 +31,7 @@ pub fn define(immediates: &OperandKinds, entities: &OperandKinds) -> FormatRegis
 
     registry.insert(Builder::new("Unary").value());
     registry.insert(Builder::new("UnaryImm").imm(imm64));
+    registry.insert(Builder::new("UnaryImm128").imm(uimm128));
     registry.insert(Builder::new("UnaryIeee32").imm(ieee32));
     registry.insert(Builder::new("UnaryIeee64").imm(ieee64));
     registry.insert(Builder::new("UnaryBool").imm(boolean));

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

@@ -29,6 +29,16 @@ pub fn define() -> Vec<OperandKind> {
         .build();
     kinds.push(uimm32);
 
+    // An unsigned 128-bit immediate integer operand.
+    //
+    // This operand is used to pass entire 128-bit vectors as immediates to
+    // instructions like const.
+    let uimm128 = Builder::new_imm("uimm128")
+        .doc("A 128-bit immediate unsigned integer.")
+        .rust_type("ir::Constant")
+        .build();
+    kinds.push(uimm128);
+
     // A 32-bit immediate signed offset.
     //
     // This is used to represent an immediate address offset in load/store

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

@@ -30,6 +30,7 @@ pub fn define(
     let uimm8 = immediates.by_name("uimm8");
     let uimm32 = immediates.by_name("uimm32");
     let imm64 = immediates.by_name("imm64");
+    let uimm128 = immediates.by_name("uimm128");
     let offset32 = immediates.by_name("offset32");
     let memflags = immediates.by_name("memflags");
     let ieee32 = immediates.by_name("ieee32");
@@ -1088,6 +1089,22 @@ pub fn define(
         .operands_out(vec![a]),
     );
 
+    let N = &operand_doc("N", uimm128, "The 16 immediate bytes of a 128-bit vector");
+    let a = &operand_doc("a", TxN, "A constant vector value");
+
+    ig.push(
+        Inst::new(
+            "vconst",
+            r#"
+        SIMD vector constant.
+
+        Construct a vector with the given immediate bytes.
+        "#,
+        )
+        .operands_in(vec![N])
+        .operands_out(vec![a]),
+    );
+
     let a = &operand_doc("a", Ref, "A constant reference null value");
 
     ig.push(