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8358179: Performance regression in Math.cbrt #25962

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8358179: Performance regression in Math.cbrt #25962

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4eaca6b
Check for special values first in x86_64 cbrt intrinsic
missa-prime Jun 24, 2025
59201ed
Make absolute mask memory constant 16 byte aligned for compatibility …
missa-prime Jun 24, 2025
615169d
Ensure ABS_MASK is a 128-bit memory sized location and only use equal…
missa-prime Jun 27, 2025
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53 changes: 14 additions & 39 deletions src/hotspot/cpu/x86/stubGenerator_x86_64_cbrt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,12 @@
//
/******************************************************************************/

/* Represents 0x7FFFFFFFFFFFFFFF double precision in lower 64 bits*/
ATTRIBUTE_ALIGNED(16) static const juint _ABS_MASK[] =
{
4294967295, 2147483647, 0, 0
};

ATTRIBUTE_ALIGNED(4) static const juint _SIG_MASK[] =
{
0, 1032192
Expand Down Expand Up @@ -188,10 +194,10 @@ address StubGenerator::generate_libmCbrt() {
StubCodeMark mark(this, stub_id);
address start = __ pc();

Label L_2TAG_PACKET_0_0_1, L_2TAG_PACKET_1_0_1, L_2TAG_PACKET_2_0_1, L_2TAG_PACKET_3_0_1;
Label L_2TAG_PACKET_4_0_1, L_2TAG_PACKET_5_0_1, L_2TAG_PACKET_6_0_1;
Label L_2TAG_PACKET_0_0_1, L_2TAG_PACKET_1_0_1, L_2TAG_PACKET_2_0_1;
Label B1_1, B1_2, B1_4;

address ABS_MASK = (address)_ABS_MASK;
address SIG_MASK = (address)_SIG_MASK;
address EXP_MASK = (address)_EXP_MASK;
address EXP_MSK2 = (address)_EXP_MSK2;
Expand All @@ -208,8 +214,12 @@ address StubGenerator::generate_libmCbrt() {
__ enter(); // required for proper stackwalking of RuntimeStub frame

__ bind(B1_1);
__ subq(rsp, 24);
__ movsd(Address(rsp), xmm0);
__ ucomisd(xmm0, ExternalAddress(ZERON), r11 /*rscratch*/);
__ jcc(Assembler::equal, L_2TAG_PACKET_1_0_1); // Branch only if x is +/- zero or NaN
__ movq(xmm1, xmm0);
__ andpd(xmm1, ExternalAddress(ABS_MASK), r11 /*rscratch*/);
__ ucomisd(xmm1, ExternalAddress(INF), r11 /*rscratch*/);
__ jcc(Assembler::equal, B1_4); // Branch only if x is +/- INF

__ bind(B1_2);
__ movq(xmm7, xmm0);
Expand All @@ -228,8 +238,6 @@ address StubGenerator::generate_libmCbrt() {
__ andl(rdx, rax);
__ cmpl(rdx, 0);
__ jcc(Assembler::equal, L_2TAG_PACKET_0_0_1); // Branch only if |x| is denormalized
__ cmpl(rdx, 524032);
__ jcc(Assembler::equal, L_2TAG_PACKET_1_0_1); // Branch only if |x| is INF or NaN
__ shrl(rdx, 8);
__ shrq(r9, 8);
__ andpd(xmm2, xmm0);
Expand Down Expand Up @@ -297,8 +305,6 @@ address StubGenerator::generate_libmCbrt() {
__ andl(rdx, rax);
__ shrl(rdx, 8);
__ shrq(r9, 8);
__ cmpl(rdx, 0);
__ jcc(Assembler::equal, L_2TAG_PACKET_3_0_1); // Branch only if |x| is zero
__ andpd(xmm2, xmm0);
__ andpd(xmm0, xmm5);
__ orpd(xmm3, xmm2);
Expand All @@ -322,41 +328,10 @@ address StubGenerator::generate_libmCbrt() {
__ psllq(xmm7, 52);
__ jmp(L_2TAG_PACKET_2_0_1);

__ bind(L_2TAG_PACKET_3_0_1);
__ cmpq(r9, 0);
__ jcc(Assembler::notEqual, L_2TAG_PACKET_4_0_1); // Branch only if x is negative zero
__ xorpd(xmm0, xmm0);
__ jmp(B1_4);

__ bind(L_2TAG_PACKET_4_0_1);
__ movsd(xmm0, ExternalAddress(ZERON), r11 /*rscratch*/);
__ jmp(B1_4);

__ bind(L_2TAG_PACKET_1_0_1);
__ movl(rax, Address(rsp, 4));
__ movl(rdx, Address(rsp));
__ movl(rcx, rax);
__ andl(rcx, 2147483647);
__ cmpl(rcx, 2146435072);
__ jcc(Assembler::above, L_2TAG_PACKET_5_0_1); // Branch only if |x| is NaN
__ cmpl(rdx, 0);
__ jcc(Assembler::notEqual, L_2TAG_PACKET_5_0_1); // Branch only if |x| is NaN
__ cmpl(rax, 2146435072);
__ jcc(Assembler::notEqual, L_2TAG_PACKET_6_0_1); // Branch only if x is negative INF
__ movsd(xmm0, ExternalAddress(INF), r11 /*rscratch*/);
__ jmp(B1_4);

__ bind(L_2TAG_PACKET_6_0_1);
__ movsd(xmm0, ExternalAddress(NEG_INF), r11 /*rscratch*/);
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@mur47x111 mur47x111 Jul 2, 2025

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note that NEG_INF is now unused

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@missa-prime missa-prime Jul 2, 2025

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Got it - thanks.

__ jmp(B1_4);

__ bind(L_2TAG_PACKET_5_0_1);
__ movsd(xmm0, Address(rsp));
__ addsd(xmm0, xmm0);
__ movq(Address(rsp, 8), xmm0);

__ bind(B1_4);
__ addq(rsp, 24);
__ leave(); // required for proper stackwalking of RuntimeStub frame
__ ret(0);

Expand Down