Add comment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84246 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMSubtarget.cpp b/lib/Target/ARM/ARMSubtarget.cpp
index cf1ee3f..698e5e2 100644
--- a/lib/Target/ARM/ARMSubtarget.cpp
+++ b/lib/Target/ARM/ARMSubtarget.cpp
@@ -101,6 +101,8 @@
   // Set CPU specific features.
   if (CPUString == "cortex-a8") {
     PostRAScheduler = true;
+    // On Cortext-a8, it's faster to perform some single-precision FP
+    // operations with NEON instructions.
     if (UseNEONFP.getPosition() == 0)
       UseNEONForSinglePrecisionFP = true;
   }