Use 'xor r, r' to set registers to 0 instead of mov (#766)

cranelift/codegen/src/predicates.rs

@@ -11,6 +11,12 @@
 
 use crate::ir;
 
+/// Check that an integer value is zero.
+#[allow(dead_code)]
+pub fn is_zero_int<T: Into<i64>>(x: T) -> bool {
+    x.into() == 0
+}
+
 /// Check that a 64-bit floating point value is zero.
 #[allow(dead_code)]
 pub fn is_zero_64_bit_float<T: Into<ir::immediates::Ieee64>>(x: T) -> bool {