diff --git a/docs/LangRef.html b/docs/LangRef.html
index bdc9e170642..1331b021c10 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -5045,6 +5045,13 @@ Loop:       ; Infinite loop that counts from 0 on up...
   %ZZ = call zeroext i32 @bar()                     <i>; Return value is %zero extended</i>
 </pre>
 
+<p>llvm treats calls to some functions with names and arguments that match the
+standard C library as being the C library functions, and may perform
+optimizations or generate code for them under that assumption.  These
+functions currently include:
+acos, asin, atan, atan2, ceil, cos, cosf, cosh, exp, fabs, floor, fmod, log,
+log10, malloc, pow, sin, sinh, sqrt, sqrtf, sin, sinf, tan, tanh.</p>
+
 </div>
 
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