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8346475: RISC-V: Small improvement for MacroAssembler::ctzc_bit #22800

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8346475: RISC-V: Small improvement for MacroAssembler::ctzc_bit #22800

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8346475: RISC-V: Small improvement for MacroAssembler::ctzc_bit
RealFYang Dec 18, 2024
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RealFYang Dec 18, 2024
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RealFYang Dec 18, 2024
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6 changes: 4 additions & 2 deletions src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -787,7 +787,8 @@ void C2_MacroAssembler::string_indexof_char(Register str1, Register cnt1,
j(NOMATCH);

bind(HIT);
ctzc_bit(trailing_char, match_mask, isL, ch1, result);
// count bits of trailing zero chars
ctzc_bits(trailing_char, match_mask, isL, ch1, result);
srli(trailing_char, trailing_char, 3);
addi(cnt1, cnt1, 8);
ble(cnt1, trailing_char, NOMATCH);
Expand Down Expand Up @@ -1536,7 +1537,8 @@ void C2_MacroAssembler::string_compare(Register str1, Register str2,
// compute their difference.
bind(DIFFERENCE);
xorr(tmp3, tmp1, tmp2);
ctzc_bit(result, tmp3, isLL); // count zero from lsb to msb
// count bits of trailing zero chars
ctzc_bits(result, tmp3, isLL);
srl(tmp1, tmp1, result);
srl(tmp2, tmp2, result);
if (isLL) {
Expand Down
22 changes: 10 additions & 12 deletions src/hotspot/cpu/riscv/macroAssembler_riscv.cpp
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Expand Up @@ -5395,28 +5395,26 @@ void MacroAssembler::multiply_to_len(Register x, Register xlen, Register y, Regi
}
#endif

// Count bits of trailing zero chars from lsb to msb until first non-zero element.
// For LL case, one byte for one element, so shift 8 bits once, and for other case,
// shift 16 bits once.
void MacroAssembler::ctzc_bit(Register Rd, Register Rs, bool isLL, Register tmp1, Register tmp2) {
// Count bits of trailing zero chars from lsb to msb until first non-zero
// char seen. For the LL case, shift 8 bits once as there is only one byte
// per each char. For other cases, shift 16 bits once.
void MacroAssembler::ctzc_bits(Register Rd, Register Rs, bool isLL,
Register tmp1, Register tmp2) {
int step = isLL ? 8 : 16;
if (UseZbb) {
assert_different_registers(Rd, Rs, tmp1);
int step = isLL ? 8 : 16;
ctz(Rd, Rs);
andi(tmp1, Rd, step - 1);
sub(Rd, Rd, tmp1);
andi(Rd, Rd, -step);
return;
}

assert_different_registers(Rd, Rs, tmp1, tmp2);
assert_different_registers(Rd, tmp1, tmp2);
Label Loop;
int step = isLL ? 8 : 16;
mv(Rd, -step);
mv(tmp2, Rs);
mv(Rd, -step);

bind(Loop);
addi(Rd, Rd, step);
andi(tmp1, tmp2, ((1 << step) - 1));
zext(tmp1, tmp2, step);
srli(tmp2, tmp2, step);
beqz(tmp1, Loop);
}
Expand Down
3 changes: 2 additions & 1 deletion src/hotspot/cpu/riscv/macroAssembler_riscv.hpp
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Expand Up @@ -1362,7 +1362,8 @@ class MacroAssembler: public Assembler {
void inflate_lo32(Register Rd, Register Rs, Register tmp1 = t0, Register tmp2 = t1);
void inflate_hi32(Register Rd, Register Rs, Register tmp1 = t0, Register tmp2 = t1);

void ctzc_bit(Register Rd, Register Rs, bool isLL = false, Register tmp1 = t0, Register tmp2 = t1);
void ctzc_bits(Register Rd, Register Rs, bool isLL = false,
Register tmp1 = t0, Register tmp2 = t1);

void zero_words(Register base, uint64_t cnt);
address zero_words(Register ptr, Register cnt);
Expand Down
21 changes: 14 additions & 7 deletions src/hotspot/cpu/riscv/stubGenerator_riscv.cpp
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Expand Up @@ -2568,7 +2568,8 @@ class StubGenerator: public StubCodeGenerator {
// Find the first different characters in the longwords and
// compute their difference.
__ bind(CALCULATE_DIFFERENCE);
__ ctzc_bit(tmp4, tmp3);
// count bits of trailing zero chars
__ ctzc_bits(tmp4, tmp3);
__ srl(tmp1, tmp1, tmp4);
__ srl(tmp2, tmp2, tmp4);
__ zext(tmp1, tmp1, 16);
Expand Down Expand Up @@ -2703,7 +2704,8 @@ class StubGenerator: public StubCodeGenerator {
// Find the first different characters in the longwords and
// compute their difference.
__ bind(DIFF2);
__ ctzc_bit(tmp3, tmp4, isLL); // count zero from lsb to msb
// count bits of trailing zero chars
__ ctzc_bits(tmp3, tmp4, isLL);
__ srl(tmp5, tmp5, tmp3);
__ srl(cnt1, cnt1, tmp3);
if (isLL) {
Expand All @@ -2716,7 +2718,8 @@ class StubGenerator: public StubCodeGenerator {
__ sub(result, tmp5, cnt1);
__ j(LENGTH_DIFF);
__ bind(DIFF);
__ ctzc_bit(tmp3, tmp4, isLL); // count zero from lsb to msb
// count bits of trailing zero chars
__ ctzc_bits(tmp3, tmp4, isLL);
__ srl(tmp1, tmp1, tmp3);
__ srl(tmp2, tmp2, tmp3);
if (isLL) {
Expand Down Expand Up @@ -2862,7 +2865,8 @@ class StubGenerator: public StubCodeGenerator {
__ beqz(match_mask, NOMATCH);

__ bind(L_SMALL_HAS_ZERO_LOOP);
__ ctzc_bit(trailing_zeros, match_mask, haystack_isL, ch2, tmp); // count trailing zeros
// count bits of trailing zero chars
__ ctzc_bits(trailing_zeros, match_mask, haystack_isL, ch2, tmp);
__ addi(trailing_zeros, trailing_zeros, haystack_isL ? 7 : 15);
__ mv(ch2, wordSize / haystack_chr_size);
__ ble(needle_len, ch2, L_SMALL_CMP_LOOP_LAST_CMP2);
Expand All @@ -2881,7 +2885,8 @@ class StubGenerator: public StubCodeGenerator {

__ bind(L_SMALL_CMP_LOOP_NOMATCH);
__ beqz(match_mask, NOMATCH);
__ ctzc_bit(trailing_zeros, match_mask, haystack_isL, tmp, ch2);
// count bits of trailing zero chars
__ ctzc_bits(trailing_zeros, match_mask, haystack_isL, tmp, ch2);
__ addi(trailing_zeros, trailing_zeros, haystack_isL ? 7 : 15);
__ add(result, result, 1);
__ add(haystack, haystack, haystack_chr_size);
Expand All @@ -2900,7 +2905,8 @@ class StubGenerator: public StubCodeGenerator {

__ align(OptoLoopAlignment);
__ bind(L_HAS_ZERO);
__ ctzc_bit(trailing_zeros, match_mask, haystack_isL, tmp, ch2);
// count bits of trailing zero chars
__ ctzc_bits(trailing_zeros, match_mask, haystack_isL, tmp, ch2);
__ addi(trailing_zeros, trailing_zeros, haystack_isL ? 7 : 15);
__ slli(needle_len, needle_len, BitsPerByte * wordSize / 2);
__ orr(haystack_len, haystack_len, needle_len); // restore needle_len(32bits)
Expand Down Expand Up @@ -2929,7 +2935,8 @@ class StubGenerator: public StubCodeGenerator {

__ bind(L_CMP_LOOP_NOMATCH);
__ beqz(match_mask, L_HAS_ZERO_LOOP_NOMATCH);
__ ctzc_bit(trailing_zeros, match_mask, haystack_isL, needle_len, ch2); // find next "first" char index
// count bits of trailing zero chars
__ ctzc_bits(trailing_zeros, match_mask, haystack_isL, needle_len, ch2);
__ addi(trailing_zeros, trailing_zeros, haystack_isL ? 7 : 15);
__ add(haystack, haystack, haystack_chr_size);
__ j(L_HAS_ZERO_LOOP);
Expand Down