diff --git a/src/x86/cg.c b/src/x86/cg.c
index 78514d1..cdea206 100644
--- a/src/x86/cg.c
+++ b/src/x86/cg.c
@@ -129,6 +129,10 @@ static AST *is_field_access(AST *e) {
 	return NULL;
 }
 
+/*
+ * Convert a XOP-able expression into an x86 operand.
+ * Result MUST be determinstic and always the same, for the same given expression.
+ * */
 static const char *xop_sz(AST *tlc, AST *e, int sz) {
 #define XOPBUFS 16
 #define XOPBUFSZ 32