Add an IsEqual FieldPredicate.

Compare an immediate operand to a constant value.

lib/cretonne/meta/cdsl/predicates.py

@@ -232,6 +232,21 @@ class FieldPredicate(object):
         return 'predicates::{}({})'.format(self.function, ', '.join(args))
 
 
+class IsEqual(FieldPredicate):
+    """
+    Instruction predicate that checks if an immediate instruction format field
+    is equal to a constant value.
+
+    :param field: `FormatField` to be checked.
+    :param value: The constant value to compare against.
+    """
+
+    def __init__(self, field, value):
+        # type: (FormatField, Any) -> None
+        super(IsEqual, self).__init__(field, 'is_equal', (value,))
+        self.value = value
+
+
 class IsSignedInt(FieldPredicate):
     """
     Instruction predicate that checks if an immediate instruction format field

lib/cretonne/src/predicates.rs

@@ -9,6 +9,12 @@
 //! Some of these predicates may be unused in certain ISA configurations, so we suppress the
 //! dead_code warning.
 
+/// Check that `x` is the same as `y`.
+#[allow(dead_code)]
+pub fn is_equal<T: Eq + Copy>(x: T, y: T) -> bool {
+    x == y
+}
+
 /// Check that `x` can be represented as a `wd`-bit signed integer with `sc` low zero bits.
 #[allow(dead_code)]
 pub fn is_signed_int<T: Into<i64>>(x: T, wd: u8, sc: u8) -> bool {