From: W. Felix Handte <w@felixhandte.com>
Date: Tue, 9 Nov 2021 17:15:18 +0000 (-0500)
Subject: Rewrite Fix to Still Auto-Vectorize
X-Git-Tag: v1.5.1~1^2~62^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=48572f52b1c6fe2c7e57206b063ea85980e6c00b;p=thirdparty%2Fzstd.git

Rewrite Fix to Still Auto-Vectorize
---

diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 59a216918..09f18d6d9 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -2332,12 +2332,17 @@ ZSTD_reduceTable_internal (U32* const table, U32 const size, U32 const reducerVa
     for (rowNb=0 ; rowNb < nbRows ; rowNb++) {
         int column;
         for (column=0; column<ZSTD_ROWSIZE; column++) {
+            U32 newVal;
             if (preserveMark && table[cellNb] == ZSTD_DUBT_UNSORTED_MARK) {
+                /* This write is pointless, but is required(?) for the compiler
+                 * to auto-vectorize the loop. */
+                newVal = ZSTD_DUBT_UNSORTED_MARK;
             } else if (table[cellNb] < reducerThreshold) {
-                table[cellNb] = 0;
+                newVal = 0;
             } else {
-                table[cellNb] -= reducerValue;
+                newVal = table[cellNb] - reducerValue;
             }
+            table[cellNb] = newVal;
             cellNb++;
     }   }
 }