From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 10 Jan 2019 16:57:28 +0000 (+0000)
Subject: [Docs] add note to avoid 'errno' for better vectorization (PR40265)
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=b56fdf02a5eb7c7c2a9be23e3477ad2588385ab3;p=llvm

[Docs] add note to avoid 'errno' for better vectorization (PR40265)

This is a partial fix for the documentation improvements requested in:
https://bugs.llvm.org/show_bug.cgi?id=40265


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350845 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/docs/Vectorizers.rst b/docs/Vectorizers.rst
index 42e8d02f337..4a015800741 100644
--- a/docs/Vectorizers.rst
+++ b/docs/Vectorizers.rst
@@ -340,6 +340,10 @@ instruction is available.
       f[i] = floorf(f[i]);
   }
 
+Note that the optimizer may not be able to vectorize math library functions 
+that access external state such as "errno". To allow better optimization of 
+C/C++ math library functions, use "-fno-math-errno".
+
 Partial unrolling during vectorization
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^