From 84b135695d79c2c416b7746ebad8f39f9d2ab57e Mon Sep 17 00:00:00 2001
From: Ben Gamari <ben@smart-cactus.org>
Date: Mon, 4 Jul 2016 20:33:57 -0400
Subject: FastString: Reduce allocations of concatFS

Instead of unpacking and then repacking we simply concatenate all of the
individual ByteStrings.
---
 compiler/utils/FastString.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/utils/FastString.hs b/compiler/utils/FastString.hs
index 40c3882b87..407c185ee8 100644
--- a/compiler/utils/FastString.hs
+++ b/compiler/utils/FastString.hs
@@ -513,7 +513,7 @@ appendFS fs1 fs2 = mkFastStringByteString
                              (fastStringToByteString fs2)
 
 concatFS :: [FastString] -> FastString
-concatFS ls = mkFastString (Prelude.concat (map unpackFS ls)) -- ToDo: do better
+concatFS = mkFastStringByteString . BS.concat . map fs_bs
 
 headFS :: FastString -> Char
 headFS (FastString _ 0 _ _) = panic "headFS: Empty FastString"
-- 
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