diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -9583,7 +9583,10 @@
 """""""""
 
 The '``frem``' instruction returns the remainder from the division of
-its two operands.
+its two operands. On some target, such as X86, the instruction is 
+implemented as call to '``libm``' '``fmod``' function, but the 
+output is equivalent to the mathematical remainder.
+
 
 Arguments:
 """"""""""