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core: Make popcnt* take two cycles

Browse Source 
This moves the calculation of the result for popcnt* into the
countbits unit, renamed from countzero, so that we can take two cycles
to get the result.  The motivation for this is that the popcnt*
calculation was showing up as a critical path.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
fpu-constant
Paul Mackerras 2 years ago committed by Anton Blanchard
parent 6ff3b2499c
commit 2491aa7fc5
8 changed files with 153 additions and 120 deletions
Show Stats Download Patch File Download Diff File

2
Makefile
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@ -60,7 +60,7 @@ core_files = decode_types.vhdl common.vhdl wishbone_types.vhdl fetch1.vhdl \
decode1.vhdl helpers.vhdl insn_helpers.vhdl \
control.vhdl decode2.vhdl register_file.vhdl \
cr_file.vhdl crhelpers.vhdl ppc_fx_insns.vhdl rotator.vhdl \
logical.vhdl countzero.vhdl multiply.vhdl divider.vhdl execute1.vhdl \
logical.vhdl countbits.vhdl multiply.vhdl divider.vhdl execute1.vhdl \
loadstore1.vhdl mmu.vhdl dcache.vhdl writeback.vhdl core_debug.vhdl \
core.vhdl fpu.vhdl pmu.vhdl


130
countbits.vhdl
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@ -0,0 +1,130 @@
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;
use work.helpers.all;

entity bit_counter is
port (
clk : in std_logic;
rs : in std_ulogic_vector(63 downto 0);
count_right : in std_ulogic;
do_popcnt : in std_ulogic;
is_32bit : in std_ulogic;
datalen : in std_ulogic_vector(3 downto 0);
result : out std_ulogic_vector(63 downto 0)
);
end entity bit_counter;

architecture behaviour of bit_counter is
-- signals for count-leading/trailing-zeroes
signal inp : std_ulogic_vector(63 downto 0);
signal sum : std_ulogic_vector(64 downto 0);
signal msb_r : std_ulogic;
signal onehot : std_ulogic_vector(63 downto 0);
signal onehot_r : std_ulogic_vector(63 downto 0);
signal bitnum : std_ulogic_vector(5 downto 0);
signal cntz : std_ulogic_vector(63 downto 0);

-- signals for popcnt
signal dlen_r : std_ulogic_vector(3 downto 0);
signal pcnt_r : std_ulogic;
subtype twobit is unsigned(1 downto 0);
type twobit32 is array(0 to 31) of twobit;
signal pc2 : twobit32;
subtype threebit is unsigned(2 downto 0);
type threebit16 is array(0 to 15) of threebit;
signal pc4 : threebit16;
subtype fourbit is unsigned(3 downto 0);
type fourbit8 is array(0 to 7) of fourbit;
signal pc8 : fourbit8;
signal pc8_r : fourbit8;
subtype sixbit is unsigned(5 downto 0);
type sixbit2 is array(0 to 1) of sixbit;
signal pc32 : sixbit2;
signal popcnt : std_ulogic_vector(63 downto 0);

begin
countzero_r: process(clk)
begin
if rising_edge(clk) then
msb_r <= sum(64);
onehot_r <= onehot;
end if;
end process;

countzero: process(all)
begin
if is_32bit = '0' then
if count_right = '0' then
inp <= bit_reverse(rs);
else
inp <= rs;
end if;
else
inp(63 downto 32) <= x"FFFFFFFF";
if count_right = '0' then
inp(31 downto 0) <= bit_reverse(rs(31 downto 0));
else
inp(31 downto 0) <= rs(31 downto 0);
end if;
end if;

sum <= std_ulogic_vector(unsigned('0' & not inp) + 1);
onehot <= sum(63 downto 0) and inp;

-- The following occurs after a clock edge
bitnum <= bit_number(onehot_r);

cntz <= 57x"0" & msb_r & bitnum;
end process;

popcnt_r: process(clk)
begin
if rising_edge(clk) then
for i in 0 to 7 loop
pc8_r(i) <= pc8(i);
end loop;
dlen_r <= datalen;
pcnt_r <= do_popcnt;
end if;
end process;

popcnt_a: process(all)
begin
for i in 0 to 31 loop
pc2(i) <= unsigned("0" & rs(i * 2 downto i * 2)) + unsigned("0" & rs(i * 2 + 1 downto i * 2 + 1));
end loop;
for i in 0 to 15 loop
pc4(i) <= ('0' & pc2(i * 2)) + ('0' & pc2(i * 2 + 1));
end loop;
for i in 0 to 7 loop
pc8(i) <= ('0' & pc4(i * 2)) + ('0' & pc4(i * 2 + 1));
end loop;

-- after a clock edge
for i in 0 to 1 loop
pc32(i) <= ("00" & pc8_r(i * 4)) + ("00" & pc8_r(i * 4 + 1)) +
("00" & pc8_r(i * 4 + 2)) + ("00" & pc8_r(i * 4 + 3));
end loop;
popcnt <= (others => '0');
if dlen_r(3 downto 2) = "00" then
-- popcntb
for i in 0 to 7 loop
popcnt(i * 8 + 3 downto i * 8) <= std_ulogic_vector(pc8_r(i));
end loop;
elsif dlen_r(3) = '0' then
-- popcntw
for i in 0 to 1 loop
popcnt(i * 32 + 5 downto i * 32) <= std_ulogic_vector(pc32(i));
end loop;
else
popcnt(6 downto 0) <= std_ulogic_vector(('0' & pc32(0)) + ('0' & pc32(1)));
end if;
end process;

result <= cntz when pcnt_r = '0' else popcnt;

end behaviour;

12
countzero_tb.vhdl → countbits_tb.vhdl
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@ -11,11 +11,11 @@ use work.common.all;
library osvvm;
use osvvm.RandomPkg.all;

entity countzero_tb is
entity countbits_tb is
generic (runner_cfg : string := runner_cfg_default);
end countzero_tb;
end countbits_tb;

architecture behave of countzero_tb is
architecture behave of countbits_tb is
constant clk_period: time := 10 ns;
signal rs: std_ulogic_vector(63 downto 0);
signal is_32bit, count_right: std_ulogic := '0';
@ -23,13 +23,15 @@ architecture behave of countzero_tb is
signal clk: std_ulogic;

begin
zerocounter_0: entity work.zero_counter
bitcounter_0: entity work.bit_counter
port map (
clk => clk,
rs => rs,
result => res,
count_right => count_right,
is_32bit => is_32bit
is_32bit => is_32bit,
do_popcnt => '0',
datalen => "0000"
);

clk_process: process

60
countzero.vhdl
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@ -1,60 +0,0 @@
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;
use work.helpers.all;

entity zero_counter is
port (
clk : in std_logic;
rs : in std_ulogic_vector(63 downto 0);
count_right : in std_ulogic;
is_32bit : in std_ulogic;
result : out std_ulogic_vector(63 downto 0)
);
end entity zero_counter;

architecture behaviour of zero_counter is
signal inp : std_ulogic_vector(63 downto 0);
signal sum : std_ulogic_vector(64 downto 0);
signal msb_r : std_ulogic;
signal onehot : std_ulogic_vector(63 downto 0);
signal onehot_r : std_ulogic_vector(63 downto 0);
signal bitnum : std_ulogic_vector(5 downto 0);

begin
countzero_r: process(clk)
begin
if rising_edge(clk) then
msb_r <= sum(64);
onehot_r <= onehot;
end if;
end process;

countzero: process(all)
begin
if is_32bit = '0' then
if count_right = '0' then
inp <= bit_reverse(rs);
else
inp <= rs;
end if;
else
inp(63 downto 32) <= x"FFFFFFFF";
if count_right = '0' then
inp(31 downto 0) <= bit_reverse(rs(31 downto 0));
else
inp(31 downto 0) <= rs(31 downto 0);
end if;
end if;

sum <= std_ulogic_vector(unsigned('0' & not inp) + 1);
onehot <= sum(63 downto 0) and inp;

-- The following occurs after a clock edge
bitnum <= bit_number(onehot_r);

result <= x"00000000000000" & "0" & msb_r & bitnum;
end process;
end behaviour;

4
decode2.vhdl
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@ -215,7 +215,6 @@ architecture behaviour of decode2 is
OP_AND => "001", -- logical_result
OP_OR => "001",
OP_XOR => "001",
OP_POPCNT => "001",
OP_PRTY => "001",
OP_CMPB => "001",
OP_EXTS => "001",
@ -234,7 +233,8 @@ architecture behaviour of decode2 is
OP_DIV => "011",
OP_DIVE => "011",
OP_MOD => "011",
OP_CNTZ => "100", -- countzero_result
OP_CNTZ => "100", -- countbits_result
OP_POPCNT => "100",
OP_MFSPR => "101", -- spr_result
OP_B => "110", -- next_nia
OP_BC => "110",

19
execute1.vhdl
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@ -106,7 +106,8 @@ architecture behaviour of execute1 is
signal rotator_result: std_ulogic_vector(63 downto 0);
signal rotator_carry: std_ulogic;
signal logical_result: std_ulogic_vector(63 downto 0);
signal countzero_result: std_ulogic_vector(63 downto 0);
signal do_popcnt: std_ulogic;
signal countbits_result: std_ulogic_vector(63 downto 0);
signal alu_result: std_ulogic_vector(63 downto 0);
signal adder_result: std_ulogic_vector(63 downto 0);
signal misc_result: std_ulogic_vector(63 downto 0);
@ -284,13 +285,15 @@ begin
datalen => e_in.data_len
);

countzero_0: entity work.zero_counter
countbits_0: entity work.bit_counter
port map (
clk => clk,
rs => c_in,
count_right => e_in.insn(10),
is_32bit => e_in.is_32bit,
result => countzero_result
do_popcnt => do_popcnt,
datalen => e_in.data_len,
result => countbits_result
);

multiply_0: entity work.multiply
@ -391,7 +394,7 @@ begin
logical_result when "001",
rotator_result when "010",
muldiv_result when "011",
countzero_result when "100",
countbits_result when "100",
spr_result when "101",
next_nia when "110",
misc_result when others;
@ -813,6 +816,8 @@ begin
rot_clear_right <= '1' when e_in.insn_type = OP_RLC or e_in.insn_type = OP_RLCR else '0';
rot_sign_ext <= '1' when e_in.insn_type = OP_EXTSWSLI else '0';

do_popcnt <= '1' when e_in.insn_type = OP_POPCNT else '0';

illegal := '0';
if r.intr_pending = '1' then
v.e.srr1 := r.e.srr1;
@ -963,7 +968,7 @@ begin
when OP_ADDG6S =>
when OP_CMPRB =>
when OP_CMPEQB =>
when OP_AND | OP_OR | OP_XOR | OP_POPCNT | OP_PRTY | OP_CMPB | OP_EXTS |
when OP_AND | OP_OR | OP_XOR | OP_PRTY | OP_CMPB | OP_EXTS |
OP_BPERM | OP_BCD =>

when OP_B =>
@ -1025,7 +1030,7 @@ begin
end if;
do_trace := '0';

when OP_CNTZ =>
when OP_CNTZ | OP_POPCNT =>
v.e.valid := '0';
v.cntz_in_progress := '1';
v.busy := '1';
@ -1220,7 +1225,7 @@ begin
-- valid_in = 0. Hence they don't happen in the same cycle as any of
-- the cases above which depend on valid_in = 1.
if r.cntz_in_progress = '1' then
-- cnt[lt]z always takes two cycles
-- cnt[lt]z and popcnt* always take two cycles
v.e.valid := '1';
elsif r.mul_in_progress = '1' or r.div_in_progress = '1' then
if (r.mul_in_progress = '1' and multiply_to_x.valid = '1') or

44
logical.vhdl
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@ -20,20 +20,7 @@ end entity logical;

architecture behaviour of logical is

subtype twobit is unsigned(1 downto 0);
type twobit32 is array(0 to 31) of twobit;
signal pc2 : twobit32;
subtype threebit is unsigned(2 downto 0);
type threebit16 is array(0 to 15) of threebit;
signal pc4 : threebit16;
subtype fourbit is unsigned(3 downto 0);
type fourbit8 is array(0 to 7) of fourbit;
signal pc8 : fourbit8;
subtype sixbit is unsigned(5 downto 0);
type sixbit2 is array(0 to 1) of sixbit;
signal pc32 : sixbit2;
signal par0, par1 : std_ulogic;
signal popcnt : std_ulogic_vector(63 downto 0);
signal parity : std_ulogic_vector(63 downto 0);
signal permute : std_ulogic_vector(7 downto 0);

@ -109,35 +96,6 @@ begin
variable negative : std_ulogic;
variable j : integer;
begin
-- population counts
for i in 0 to 31 loop
pc2(i) <= unsigned("0" & rs(i * 2 downto i * 2)) + unsigned("0" & rs(i * 2 + 1 downto i * 2 + 1));
end loop;
for i in 0 to 15 loop
pc4(i) <= ('0' & pc2(i * 2)) + ('0' & pc2(i * 2 + 1));
end loop;
for i in 0 to 7 loop
pc8(i) <= ('0' & pc4(i * 2)) + ('0' & pc4(i * 2 + 1));
end loop;
for i in 0 to 1 loop
pc32(i) <= ("00" & pc8(i * 4)) + ("00" & pc8(i * 4 + 1)) +
("00" & pc8(i * 4 + 2)) + ("00" & pc8(i * 4 + 3));
end loop;
popcnt <= (others => '0');
if datalen(3 downto 2) = "00" then
-- popcntb
for i in 0 to 7 loop
popcnt(i * 8 + 3 downto i * 8) <= std_ulogic_vector(pc8(i));
end loop;
elsif datalen(3) = '0' then
-- popcntw
for i in 0 to 1 loop
popcnt(i * 32 + 5 downto i * 32) <= std_ulogic_vector(pc32(i));
end loop;
else
popcnt(6 downto 0) <= std_ulogic_vector(('0' & pc32(0)) + ('0' & pc32(1)));
end if;

-- parity calculations
par0 <= rs(0) xor rs(8) xor rs(16) xor rs(24);
par1 <= rs(32) xor rs(40) xor rs(48) xor rs(56);
@ -178,8 +136,6 @@ begin
tmp := not tmp;
end if;

when OP_POPCNT =>
tmp := popcnt;
when OP_PRTY =>
tmp := parity;
when OP_CMPB =>

2
microwatt.core
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@ -18,7 +18,7 @@ filesets:
- ppc_fx_insns.vhdl
- sim_console.vhdl
- logical.vhdl
- countzero.vhdl
- countbits.vhdl
- control.vhdl
- execute1.vhdl
- fpu.vhdl

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