Add std/adler32 bench comment for the roll back
diff --git a/std/adler32/common_adler32.wuffs b/std/adler32/common_adler32.wuffs
index eb2a93b..5413e85 100644
--- a/std/adler32/common_adler32.wuffs
+++ b/std/adler32/common_adler32.wuffs
@@ -25,6 +25,10 @@
if not this.started {
this.started = true
this.state = 1
+ // There used to be an up_x86_avx2 implementation too, but while it
+ // made the std/adler32 micro-benchmarks better, it also made the
+ // std/zlib and std/png micro-benchmarks worse. See commit baec831f
+ // "Add std/adler32 hasher.up_x86_avx2".
choose up = [
up_arm_neon,
up_x86_sse42]
