[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 42e8d02..4a01580 100644
--- a/docs/Vectorizers.rst
+++ b/docs/Vectorizers.rst
@@ -340,6 +340,10 @@
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
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
