8334554: RISC-V: verify & fix perf of string comparison

Reviewed-by: rehn, luhenry, fyang

Author: Hamlin Li

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp

@@ -2326,12 +2326,13 @@ void C2_MacroAssembler::expand_bits_l_v(Register dst, Register src, Register mas
 }
 
 void C2_MacroAssembler::element_compare(Register a1, Register a2, Register result, Register cnt, Register tmp1, Register tmp2,
-                                        VectorRegister vr1, VectorRegister vr2, VectorRegister vrs, bool islatin, Label &DONE) {
+                                        VectorRegister vr1, VectorRegister vr2, VectorRegister vrs, bool islatin, Label &DONE,
+                                        Assembler::LMUL lmul) {
   Label loop;
   Assembler::SEW sew = islatin ? Assembler::e8 : Assembler::e16;
 
   bind(loop);
-  vsetvli(tmp1, cnt, sew, Assembler::m2);
+  vsetvli(tmp1, cnt, sew, lmul);
   vlex_v(vr1, a1, sew);
   vlex_v(vr2, a2, sew);
   vmsne_vv(vrs, vr1, vr2);
@@ -2357,7 +2358,7 @@ void C2_MacroAssembler::string_equals_v(Register a1, Register a2, Register resul
 
   mv(result, false);
 
-  element_compare(a1, a2, result, cnt, tmp1, tmp2, v2, v4, v2, true, DONE);
+  element_compare(a1, a2, result, cnt, tmp1, tmp2, v2, v4, v2, true, DONE, Assembler::m2);
 
   bind(DONE);
   BLOCK_COMMENT("} string_equals_v");
@@ -2410,7 +2411,7 @@ void C2_MacroAssembler::arrays_equals_v(Register a1, Register a2, Register resul
   la(a1, Address(a1, base_offset));
   la(a2, Address(a2, base_offset));
 
-  element_compare(a1, a2, result, cnt1, tmp1, tmp2, v2, v4, v2, elem_size == 1, DONE);
+  element_compare(a1, a2, result, cnt1, tmp1, tmp2, v2, v4, v2, elem_size == 1, DONE, Assembler::m2);
 
   bind(DONE);
 
@@ -2445,8 +2446,18 @@ void C2_MacroAssembler::string_compare_v(Register str1, Register str2, Register
   mv(cnt2, cnt1);
   bind(L);
 
+  // We focus on the optimization of small sized string.
+  // Please check below document for string size distribution statistics.
+  // https://cr.openjdk.org/~shade/density/string-density-report.pdf
   if (str1_isL == str2_isL) { // LL or UU
-    element_compare(str1, str2, zr, cnt2, tmp1, tmp2, v2, v4, v2, encLL, DIFFERENCE);
+    // Below construction of v regs and lmul is based on test on 2 different boards,
+    // vlen == 128 and vlen == 256 respectively.
+    if (!encLL && MaxVectorSize == 16) { // UU
+      element_compare(str1, str2, zr, cnt2, tmp1, tmp2, v4, v8, v4, encLL, DIFFERENCE, Assembler::m4);
+    } else { // UU + MaxVectorSize or LL
+      element_compare(str1, str2, zr, cnt2, tmp1, tmp2, v2, v4, v2, encLL, DIFFERENCE, Assembler::m2);
+    }
+
     j(DONE);
   } else { // LU or UL
     Register strL = encLU ? str1 : str2;

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.hpp

@@ -37,7 +37,7 @@
                        Register tmp1, Register tmp2,
                        VectorRegister vr1, VectorRegister vr2,
                        VectorRegister vrs,
-                       bool is_latin, Label& DONE);
+                       bool is_latin, Label& DONE, Assembler::LMUL lmul);
 
   void compress_bits_v(Register dst, Register src, Register mask, bool is_long);
   void expand_bits_v(Register dst, Register src, Register mask, bool is_long);

src/hotspot/cpu/riscv/riscv_v.ad

@@ -3605,14 +3605,37 @@ instruct varray_equalsC(iRegP_R11 ary1, iRegP_R12 ary2, iRegI_R10 result,
   ins_pipe(pipe_class_memory);
 %}
 
+instruct vstring_compareU_128b(iRegP_R11 str1, iRegI_R12 cnt1, iRegP_R13 str2, iRegI_R14 cnt2,
+                          iRegI_R10 result, vReg_V4 v4, vReg_V5 v5, vReg_V6 v6, vReg_V7 v7,
+                          vReg_V8 v8, vReg_V9 v9, vReg_V10 v10, vReg_V11 v11,
+                          iRegP_R28 tmp1, iRegL_R29 tmp2)
+%{
+  predicate(UseRVV && ((StrCompNode *)n)->encoding() == StrIntrinsicNode::UU &&
+            MaxVectorSize == 16);
+  match(Set result (StrComp (Binary str1 cnt1) (Binary str2 cnt2)));
+  effect(KILL tmp1, KILL tmp2, USE_KILL str1, USE_KILL str2, USE_KILL cnt1, USE_KILL cnt2,
+        TEMP v4, TEMP v5, TEMP v6, TEMP v7, TEMP v8, TEMP v9, TEMP v10, TEMP v11);
+
+  format %{ "String Compare $str1, $cnt1, $str2, $cnt2 -> $result\t#@string_compareU" %}
+  ins_encode %{
+    // Count is in 8-bit bytes; non-Compact chars are 16 bits.
+    __ string_compare_v($str1$$Register, $str2$$Register,
+                        $cnt1$$Register, $cnt2$$Register, $result$$Register,
+                        $tmp1$$Register, $tmp2$$Register,
+                        StrIntrinsicNode::UU);
+  %}
+  ins_pipe(pipe_class_memory);
+%}
+
 instruct vstring_compareU(iRegP_R11 str1, iRegI_R12 cnt1, iRegP_R13 str2, iRegI_R14 cnt2,
                           iRegI_R10 result, vReg_V2 v2, vReg_V3 v3, vReg_V4 v4, vReg_V5 v5,
                           iRegP_R28 tmp1, iRegL_R29 tmp2)
 %{
-  predicate(UseRVV && ((StrCompNode *)n)->encoding() == StrIntrinsicNode::UU);
+  predicate(UseRVV && ((StrCompNode *)n)->encoding() == StrIntrinsicNode::UU &&
+            MaxVectorSize > 16);
   match(Set result (StrComp (Binary str1 cnt1) (Binary str2 cnt2)));
   effect(KILL tmp1, KILL tmp2, USE_KILL str1, USE_KILL str2, USE_KILL cnt1, USE_KILL cnt2,
-         TEMP v2, TEMP v3, TEMP v4, TEMP v5);
+        TEMP v2, TEMP v3, TEMP v4, TEMP v5);
 
   format %{ "String Compare $str1, $cnt1, $str2, $cnt2 -> $result\t#@string_compareU" %}
   ins_encode %{
@@ -3624,14 +3647,15 @@ instruct vstring_compareU(iRegP_R11 str1, iRegI_R12 cnt1, iRegP_R13 str2, iRegI_
   %}
   ins_pipe(pipe_class_memory);
 %}
+
 instruct vstring_compareL(iRegP_R11 str1, iRegI_R12 cnt1, iRegP_R13 str2, iRegI_R14 cnt2,
                           iRegI_R10 result, vReg_V2 v2, vReg_V3 v3, vReg_V4 v4, vReg_V5 v5,
                           iRegP_R28 tmp1, iRegL_R29 tmp2)
 %{
   predicate(UseRVV && ((StrCompNode *)n)->encoding() == StrIntrinsicNode::LL);
   match(Set result (StrComp (Binary str1 cnt1) (Binary str2 cnt2)));
   effect(KILL tmp1, KILL tmp2, USE_KILL str1, USE_KILL str2, USE_KILL cnt1, USE_KILL cnt2,
-         TEMP v2, TEMP v3, TEMP v4, TEMP v5);
+        TEMP v2, TEMP v3, TEMP v4, TEMP v5);
 
   format %{ "String Compare $str1, $cnt1, $str2, $cnt2 -> $result\t#@string_compareL" %}
   ins_encode %{