8257436: [aarch64] Regressions in ArrayCopyUnalignedDst.testByte/testChar for 65-78 bytes when UseSIMDForMemoryOps is on

Reviewed-by: simonis

Author: eastig

src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp

@@ -1094,10 +1094,10 @@ class StubGenerator: public StubCodeGenerator {
                    Register count, Register tmp, int step) {
     copy_direction direction = step < 0 ? copy_backwards : copy_forwards;
     bool is_backwards = step < 0;
-    int granularity = uabs(step);
+    unsigned int granularity = uabs(step);
     const Register t0 = r3, t1 = r4;
 
-    // <= 96 bytes do inline. Direction doesn't matter because we always
+    // <= 80 (or 96 for SIMD) bytes do inline. Direction doesn't matter because we always
     // load all the data before writing anything
     Label copy4, copy8, copy16, copy32, copy80, copy_big, finish;
     const Register t2 = r5, t3 = r6, t4 = r7, t5 = r8;
@@ -1154,7 +1154,28 @@ class StubGenerator: public StubCodeGenerator {
     if (UseSIMDForMemoryOps) {
       __ ldpq(v0, v1, Address(s, 0));
       __ ldpq(v2, v3, Address(s, 32));
+      // Unaligned pointers can be an issue for copying.
+      // The issue has more chances to happen when granularity of data is
+      // less than 4(sizeof(jint)). Pointers for arrays of jint are at least
+      // 4 byte aligned. Pointers for arrays of jlong are 8 byte aligned.
+      // The most performance drop has been seen for the range 65-80 bytes.
+      // For such cases using the pair of ldp/stp instead of the third pair of
+      // ldpq/stpq fixes the performance issue.
+      if (granularity < sizeof (jint)) {
+        Label copy96;
+        __ cmp(count, u1(80/granularity));
+        __ br(Assembler::HI, copy96);
+        __ ldp(t0, t1, Address(send, -16));
+
+        __ stpq(v0, v1, Address(d, 0));
+        __ stpq(v2, v3, Address(d, 32));
+        __ stp(t0, t1, Address(dend, -16));
+        __ b(finish);
+
+        __ bind(copy96);
+      }
       __ ldpq(v4, v5, Address(send, -32));
+
       __ stpq(v0, v1, Address(d, 0));
       __ stpq(v2, v3, Address(d, 32));
       __ stpq(v4, v5, Address(dend, -32));