diff --git a/tcg/README b/tcg/README
index c2e7762a37..bc15cc3b32 100644
--- a/tcg/README
+++ b/tcg/README
@@ -254,6 +254,12 @@ t0 = t1 ? clz(t1) : t2
 
 t0 = t1 ? ctz(t1) : t2
 
+* ctpop_i32/i64 t0, t1
+
+t0 = number of bits set in t1
+With "ctpop" short for "count population", matching
+the function name used in include/qemu/host-utils.h.
+
 ********* Shifts/Rotates
 
 * shl_i32/i64 t0, t1, t2