RFR: 8187472 - AARCH64: array_equals intrinsic doesn't use prefetch for large arrays

[Andrew Haley]

On 07/02/18 19:39, Dmitrij Pochepko wrote:
> Note: medium sizes are a bit slower because of additional branch 
> added(which checks size and jumps to stub).

The indentation is messed up here:

@@ -5201,40 +5217,23 @@
   // length == 4.
   if (log_elem_size > 0)
     lsl(cnt1, cnt1, log_elem_size);
-  ldr(tmp1, Address(a1, cnt1));
-  ldr(tmp2, Address(a2, cnt1));
+    ldr(tmp1, Address(a1, cnt1));
+    ldr(tmp2, Address(a2, cnt1));
   eor(tmp1, tmp1, tmp2);
   cbnz(tmp1, DONE);
   b(SAME);

This pessimizes a very common case of string comparisons, those of
about 32 bytes.  Please think again.

I'm not convinced that reading beyond the end of the memory you're
passed is always safe.  What if you're passed an address which is the
last three bytes in a region?  It's not good enough to say that
HotSpot doesn't do that today: maybe not, but one day it might.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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