Add doc for -msse4.2 flag.
[ghc.git] / docs / users_guide / using.xml
index 47fec9a..5bd6f11 100644 (file)
@@ -2238,7 +2238,10 @@ f "2"    = 2
                                This gives a substantial performance improvement for floating
                                point, but the resulting compiled code
                                will only run on processors that support SSE2 (Intel Pentium 4 and
-                               later, or AMD Athlon 64 and later).
+                               later, or AMD Athlon 64 and later). The
+                               <link linkend="llvm-code-gen">LLVM backend</link> will also use SSE2
+                               if your processor supports it but detects this automatically so no
+                               flag is required.
           </para>
           <para>
             SSE2 is unconditionally used on x86-64 platforms.
@@ -2246,6 +2249,22 @@ f "2"    = 2
         </listitem>
       </varlistentry>
 
+      <varlistentry>
+       <term><option>-msse4.2</option>:</term>
+       <listitem>
+          <para>
+                               (x86 only, added in GHC 7.2.1) Use the SSE4.2 instruction set to
+                               implement some floating point and bit operations when using the
+                               <link linkend="native-code-gen">native code generator</link>. The
+                               resulting compiled code will only run on processors that
+                               support SSE4.2 (Intel Core i7 and later). The
+                               <link linkend="llvm-code-gen">LLVM backend</link> will also use
+                               SSE4.2 if your processor supports it but detects this automatically
+                               so no flag is required.
+          </para>
+        </listitem>
+      </varlistentry>
+
     </variablelist>
 
   </sect1>