[llvm] r350845 - [Docs] add note to avoid 'errno' for better vectorization (PR40265)

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Thu Jan 10 08:57:28 2019
New Revision: 350845

URL: http://llvm.org/viewvc/llvm-project?rev=350845&view=rev
Log:
[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

Modified:
    llvm/trunk/docs/Vectorizers.rst

Modified: llvm/trunk/docs/Vectorizers.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/Vectorizers.rst?rev=350845&r1=350844&r2=350845&view=diff
==============================================================================
--- llvm/trunk/docs/Vectorizers.rst (original)
+++ llvm/trunk/docs/Vectorizers.rst Thu Jan 10 08:57:28 2019
@@ -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
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^