lib: add hint to generate more pipeline friendly code (#3138)

With statistic data of test data files of silesia the chance of position beyond highThreshold is very low (~1.3%@L8 in most cases, all <2.5%), and is in "lowprob area". Add the branch hint so compiler can get better pipiline codegen. With this change it is observed ~1% of mozilla and xml, and slight (0.3%~0.8%) but consistent uplift on other files on Arm N1. Signed-off-by: Jun He <[email protected]> Change-Id: Id9ba1d5c767e975290b5c1bf0ecce906544f4ade
facebook · Jul 29, 2022 · ec5fdcd · ec5fdcd
1 parent 558cf20
commit ec5fdcd
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/lib/decompress/zstd_decompress_block.c b/lib/decompress/zstd_decompress_block.c
@@ -543,7 +543,7 @@ void ZSTD_buildFSETable_body(ZSTD_seqSymbol* dt,
             for (i=0; i<n; i++) {
                 tableDecode[position].baseValue = s;
                 position = (position + step) & tableMask;
-                while (position > highThreshold) position = (position + step) & tableMask;   /* lowprob area */
+                while (UNLIKELY(position > highThreshold)) position = (position + step) & tableMask;   /* lowprob area */
         }   }
         assert(position == 0); /* position must reach all cells once, otherwise normalizedCounter is incorrect */
     }