8229351: AArch64: the const STUB_THRESHOLD in macroAssembler_aarch64.…

…cpp needs to be tuned

Optimize the stub thresholds of string_compare intrinsics

Reviewed-by: adinn, aph, avoitylov

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp

@@ -4919,11 +4919,15 @@ void MacroAssembler::string_compare(Register str1, Register str2,
       DIFFERENCE, NEXT_WORD, SHORT_LOOP_TAIL, SHORT_LAST2, SHORT_LAST_INIT,
       SHORT_LOOP_START, TAIL_CHECK;
 
-  const u1 STUB_THRESHOLD = 64 + 8;
   bool isLL = ae == StrIntrinsicNode::LL;
   bool isLU = ae == StrIntrinsicNode::LU;
   bool isUL = ae == StrIntrinsicNode::UL;
 
+  // The stub threshold for LL strings is: 72 (64 + 8) chars
+  // UU: 36 chars, or 72 bytes (valid for the 64-byte large loop with prefetch)
+  // LU/UL: 24 chars, or 48 bytes (valid for the 16-character loop at least)
+  const u1 stub_threshold = isLL ? 72 : ((isLU || isUL) ? 24 : 36);
+
   bool str1_isL = isLL || isLU;
   bool str2_isL = isLL || isUL;
 
@@ -4964,7 +4968,7 @@ void MacroAssembler::string_compare(Register str1, Register str2,
       cmp(str1, str2);
       br(Assembler::EQ, DONE);
       ldr(tmp2, Address(str2));
-      cmp(cnt2, STUB_THRESHOLD);
+      cmp(cnt2, stub_threshold);
       br(GE, STUB);
       subsw(cnt2, cnt2, minCharsInWord);
       br(EQ, TAIL_CHECK);
@@ -4976,7 +4980,7 @@ void MacroAssembler::string_compare(Register str1, Register str2,
       cmp(str1, str2);
       br(Assembler::EQ, DONE);
       ldr(tmp2, Address(str2));
-      cmp(cnt2, STUB_THRESHOLD);
+      cmp(cnt2, stub_threshold);
       br(GE, STUB);
       subw(cnt2, cnt2, 4);
       eor(vtmpZ, T16B, vtmpZ, vtmpZ);
@@ -4992,7 +4996,7 @@ void MacroAssembler::string_compare(Register str1, Register str2,
       cmp(str1, str2);
       br(Assembler::EQ, DONE);
       ldrs(vtmp, Address(str2));
-      cmp(cnt2, STUB_THRESHOLD);
+      cmp(cnt2, stub_threshold);
       br(GE, STUB);
       subw(cnt2, cnt2, 4);
       lea(str1, Address(str1, cnt2, Address::uxtw(str1_chr_shift)));

src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp

@@ -4110,6 +4110,7 @@ class StubGenerator: public StubCodeGenerator {
     __ bind(NO_PREFETCH);
     __ subs(cnt2, cnt2, 16);
     __ br(__ LT, TAIL);
+    __ align(OptoLoopAlignment);
     __ bind(SMALL_LOOP); // smaller loop
       __ subs(cnt2, cnt2, 16);
       compare_string_16_x_LU(tmpL, tmpU, DIFF1, DIFF2);
@@ -4199,6 +4200,7 @@ class StubGenerator: public StubCodeGenerator {
     // less than 16 bytes left?
     __ subs(cnt2, cnt2, isLL ? 16 : 8);
     __ br(__ LT, TAIL);
+    __ align(OptoLoopAlignment);
     __ bind(SMALL_LOOP);
       compare_string_16_bytes_same(DIFF, DIFF2);
       __ subs(cnt2, cnt2, isLL ? 16 : 8);

test/hotspot/jtreg/compiler/intrinsics/string/TestStringCompareToDifferentLength.java

@@ -32,12 +32,12 @@
  *          parameters: <string length>, <maximum string length delta>
  *          Input parameters for this test are set according to Aarch64
  *          String::compareTo intrinsic implementation specifics. Aarch64
- *          implementation has 1, 4, 8 -characters loops for length < 72 and
+ *          implementation has 1, 4, 8 -bytes loops for length < 72 and
  *          16, 32, 64 -characters loops for length >= 72. Code is also affected
  *          by SoftwarePrefetchHintDistance vm flag value.
- * @run main/othervm -XX:SoftwarePrefetchHintDistance=192 compiler.intrinsics.string.TestStringCompareToDifferentLength 4 2 5 10 13 17 20 25 71 72 73 88 90 192 193 208 209
- * @run main/othervm -XX:SoftwarePrefetchHintDistance=16 compiler.intrinsics.string.TestStringCompareToDifferentLength 4 2 5 10 13 17 20 25 71 72 73 88 90
- * @run main/othervm -XX:SoftwarePrefetchHintDistance=-1 compiler.intrinsics.string.TestStringCompareToDifferentLength 4 2 5 10 13 17 20 25 71 72 73 88 90
+ * @run main/othervm -XX:SoftwarePrefetchHintDistance=192 compiler.intrinsics.string.TestStringCompareToDifferentLength 4 2 5 10 13 17 20 23 24 25 71 72 73 88 90 192 193 208 209
+ * @run main/othervm -XX:SoftwarePrefetchHintDistance=16 compiler.intrinsics.string.TestStringCompareToDifferentLength 4 2 5 10 13 17 20 23 24 25 71 72 73 88 90
+ * @run main/othervm -XX:SoftwarePrefetchHintDistance=-1 compiler.intrinsics.string.TestStringCompareToDifferentLength 4 2 5 10 13 17 20 23 24 25 71 72 73 88 90
  */
 
 package compiler.intrinsics.string;

test/hotspot/jtreg/compiler/intrinsics/string/TestStringCompareToSameLength.java

@@ -32,16 +32,16 @@
  *          String size is specified via commandline. Various size values can
  *          be specified during intrinsic development in order to test cases
  *          specific for new or modified intrinsic implementation. Aarch64
- *          implementation has 1, 4, 8 -characters loops for length < 72 and
- *          16, 32, 64 -characters loops for string length >= 72. Code is also
+ *          implementation has 1, 4, 8 -bytes loops for length < 72 and
+ *          16, 32, 64 -bytes loops for string length >= 72. Code is also
  *          affected by SoftwarePrefetchHintDistance flag value.
  *          Test class can also accept "-fullmode" parameter
  *          with maxLength paramter after it. Then it will iterate through all
  *          string length values up to maxLength parameter (inclusive). It takes
  *          a lot of time but is useful for development.
- * @run main/othervm -XX:SoftwarePrefetchHintDistance=192 compiler.intrinsics.string.TestStringCompareToSameLength 2 5 10 13 17 20 25 71 72 73 88 90 192 193 208 209
- * @run main/othervm -XX:SoftwarePrefetchHintDistance=16 compiler.intrinsics.string.TestStringCompareToSameLength 2 5 10 13 17 20 25 71 72 73 88 90
- * @run main/othervm -XX:SoftwarePrefetchHintDistance=-1 compiler.intrinsics.string.TestStringCompareToSameLength 2 5 10 13 17 20 25 71 72 73 88 90
+ * @run main/othervm -XX:SoftwarePrefetchHintDistance=192 compiler.intrinsics.string.TestStringCompareToSameLength 2 5 10 13 17 20 25 35 36 37 71 72 73 88 90 192 193 208 209
+ * @run main/othervm -XX:SoftwarePrefetchHintDistance=16 compiler.intrinsics.string.TestStringCompareToSameLength 2 5 10 13 17 20 25 35 36 37 71 72 73 88 90
+ * @run main/othervm -XX:SoftwarePrefetchHintDistance=-1 compiler.intrinsics.string.TestStringCompareToSameLength 2 5 10 13 17 20 25 35 36 37 71 72 73 88 90
  */
 
 package compiler.intrinsics.string;