Document pure/const parameter attributes

llvm-svn: 44111

llvm/docs/LangRef.html

@@ -813,6 +813,15 @@ a power of 2.</p>
     <dt><tt>nest</tt></dt>
     <dd>This indicates that the parameter can be excised using the
     <a href="#int_trampoline">trampoline intrinsics</a>.</dd>
+    <dt><tt>pure</tt></dt>
+    <dd>This function attribute indicates, that the function have no effects
+    except the return value and its return value depends only on the
+    arguments and/or global variables.</dd>
+    <dt><tt>const</tt></dt>
+    <dd>This function attribute is slightly more stricter version
+    of <tt>pure</tt> function attribute. <tt>const</tt> functions are not
+    allowed to read global memory, so such function only examines its arguments
+    and has no effects except return value.</dd>
   </dl>
 
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