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execute: Implement bypass from output of execute1 to input

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This enables back-to-back execution of integer instructions where
the first instruction writes a GPR and the second reads the same
GPR.  This is done with a set of multiplexers at the start of
execute1 which enable any of the three input operands to be taken
from the output of execute1 (i.e. r.e.write_data) rather than the
input from decode2 (i.e. e_in.read_data[123]).

This also requires changes to the hazard detection and handling.
Decode2 generates a signal indicating that the GPR being written
is available for bypass, which is true for instructions that are
executed in execute1 (rather than loadstore1/dcache).  The
gpr_hazard module stores this "bypassable" bit, and if the same
GPR needs to be read by a subsequent instruction, it outputs a
"use_bypass" signal rather than generating a stall.  The
use_bypass signal is then latched at the output of decode2 and
passed down to execute1 to control the input multiplexer.

At the moment there is no bypass on the inputs to loadstore1, but that
is OK because all load and store instructions are marked as
single-issue.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/134/head
Paul Mackerras 5 years ago
parent 0c714f1be6
commit b14d982011
6 changed files with 168 additions and 90 deletions
Show Stats Download Patch File Download Diff File

6
common.vhdl
Unescape Escape View File

@ -109,6 +109,9 @@ package common is
read_data1: std_ulogic_vector(63 downto 0);
read_data2: std_ulogic_vector(63 downto 0);
read_data3: std_ulogic_vector(63 downto 0);
bypass_data1: std_ulogic;
bypass_data2: std_ulogic;
bypass_data3: std_ulogic;
cr: std_ulogic_vector(31 downto 0);
xerc: xer_common_t;
lr: std_ulogic;
@ -126,7 +129,8 @@ package common is
data_len: std_ulogic_vector(3 downto 0);
end record;
constant Decode2ToExecute1Init : Decode2ToExecute1Type :=
(valid => '0', insn_type => OP_ILLEGAL, lr => '0', rc => '0', oe => '0', invert_a => '0',
(valid => '0', insn_type => OP_ILLEGAL, bypass_data1 => '0', bypass_data2 => '0', bypass_data3 => '0',
lr => '0', rc => '0', oe => '0', invert_a => '0',
invert_out => '0', input_carry => ZERO, output_carry => '0', input_cr => '0', output_cr => '0',
is_32bit => '0', is_signed => '0', xerc => xerc_init, others => (others => '0'));


19
control.vhdl
Unescape Escape View File

@ -21,6 +21,7 @@ entity control is

gpr_write_valid_in : in std_ulogic;
gpr_write_in : in gspr_index_t;
gpr_bypassable : in std_ulogic;

gpr_a_read_valid_in : in std_ulogic;
gpr_a_read_in : in gspr_index_t;
@ -36,7 +37,11 @@ entity control is

valid_out : out std_ulogic;
stall_out : out std_ulogic;
stopped_out : out std_ulogic
stopped_out : out std_ulogic;

gpr_bypass_a : out std_ulogic;
gpr_bypass_b : out std_ulogic;
gpr_bypass_c : out std_ulogic
);
end entity control;

@ -71,10 +76,12 @@ begin

gpr_write_valid_in => gpr_write_valid,
gpr_write_in => gpr_write_in,
bypass_avail => gpr_bypassable,
gpr_read_valid_in => gpr_a_read_valid_in,
gpr_read_in => gpr_a_read_in,

stall_out => stall_a_out
stall_out => stall_a_out,
use_bypass => gpr_bypass_a
);

gpr_hazard1: entity work.gpr_hazard
@ -87,10 +94,12 @@ begin

gpr_write_valid_in => gpr_write_valid,
gpr_write_in => gpr_write_in,
bypass_avail => gpr_bypassable,
gpr_read_valid_in => gpr_b_read_valid_in,
gpr_read_in => gpr_b_read_in,

stall_out => stall_b_out
stall_out => stall_b_out,
use_bypass => gpr_bypass_b
);

gpr_c_read_in_fmt <= "0" & gpr_c_read_in;
@ -105,10 +114,12 @@ begin

gpr_write_valid_in => gpr_write_valid,
gpr_write_in => gpr_write_in,
bypass_avail => gpr_bypassable,
gpr_read_valid_in => gpr_c_read_valid_in,
gpr_read_in => gpr_c_read_in_fmt,

stall_out => stall_c_out
stall_out => stall_c_out,
use_bypass => gpr_bypass_c
);

cr_hazard0: entity work.cr_hazard

9
core.vhdl
Unescape Escape View File

@ -9,7 +9,8 @@ use work.wishbone_types.all;
entity core is
generic (
SIM : boolean := false;
DISABLE_FLATTEN : boolean := false
DISABLE_FLATTEN : boolean := false;
EX1_BYPASS : boolean := true
);
port (
clk : in std_logic;
@ -176,6 +177,9 @@ begin
decode1_stall_in <= decode2_stall_out;

decode2_0: entity work.decode2
generic map (
EX1_BYPASS => EX1_BYPASS
)
port map (
clk => clk,
rst => core_rst,
@ -220,6 +224,9 @@ begin
);

execute1_0: entity work.execute1
generic map (
EX1_BYPASS => EX1_BYPASS
)
port map (
clk => clk,
rst => core_rst,

21
decode2.vhdl
Unescape Escape View File

@ -9,6 +9,9 @@ use work.helpers.all;
use work.insn_helpers.all;

entity decode2 is
generic (
EX1_BYPASS : boolean := true
);
port (
clk : in std_ulogic;
rst : in std_ulogic;
@ -184,15 +187,19 @@ architecture behaviour of decode2 is

signal gpr_write_valid : std_ulogic;
signal gpr_write : gspr_index_t;
signal gpr_bypassable : std_ulogic;

signal gpr_a_read_valid : std_ulogic;
signal gpr_a_read :gspr_index_t;
signal gpr_a_bypass : std_ulogic;

signal gpr_b_read_valid : std_ulogic;
signal gpr_b_read : gspr_index_t;
signal gpr_b_bypass : std_ulogic;

signal gpr_c_read_valid : std_ulogic;
signal gpr_c_read : gpr_index_t;
signal gpr_c_bypass : std_ulogic;

signal cr_write_valid : std_ulogic;
begin
@ -213,6 +220,7 @@ begin

gpr_write_valid_in => gpr_write_valid,
gpr_write_in => gpr_write,
gpr_bypassable => gpr_bypassable,

gpr_a_read_valid_in => gpr_a_read_valid,
gpr_a_read_in => gpr_a_read,
@ -228,7 +236,11 @@ begin

valid_out => control_valid_out,
stall_out => stall_out,
stopped_out => stopped_out
stopped_out => stopped_out,

gpr_bypass_a => gpr_a_bypass,
gpr_bypass_b => gpr_b_bypass,
gpr_bypass_c => gpr_c_bypass
);

decode2_0: process(clk)
@ -295,9 +307,12 @@ begin
v.e.insn_type := d_in.decode.insn_type;
v.e.read_reg1 := decoded_reg_a.reg;
v.e.read_data1 := decoded_reg_a.data;
v.e.bypass_data1 := gpr_a_bypass;
v.e.read_reg2 := decoded_reg_b.reg;
v.e.read_data2 := decoded_reg_b.data;
v.e.bypass_data2 := gpr_b_bypass;
v.e.read_data3 := decoded_reg_c.data;
v.e.bypass_data3 := gpr_c_bypass;
v.e.write_reg := decoded_reg_o.reg;
v.e.rc := decode_rc(d_in.decode.rc, d_in.insn);
if not (d_in.decode.insn_type = OP_MUL_H32 or d_in.decode.insn_type = OP_MUL_H64) then
@ -342,6 +357,10 @@ begin

gpr_write_valid <= decoded_reg_o.reg_valid;
gpr_write <= decoded_reg_o.reg;
gpr_bypassable <= '0';
if EX1_BYPASS and d_in.decode.unit = ALU then
gpr_bypassable <= '1';
end if;

gpr_a_read_valid <= decoded_reg_a.reg_valid;
gpr_a_read <= decoded_reg_a.reg;

135
execute1.vhdl
Unescape Escape View File

@ -11,6 +11,9 @@ use work.insn_helpers.all;
use work.ppc_fx_insns.all;

entity execute1 is
generic (
EX1_BYPASS : boolean := true
);
port (
clk : in std_ulogic;
rst : in std_ulogic;
@ -46,6 +49,8 @@ architecture behaviour of execute1 is

signal r, rin : reg_type;

signal a_in, b_in, c_in : std_ulogic_vector(63 downto 0);

signal ctrl: ctrl_t := (others => (others => '0'));
signal ctrl_tmp: ctrl_t := (others => (others => '0'));

@ -109,9 +114,9 @@ begin

rotator_0: entity work.rotator
port map (
rs => e_in.read_data3,
ra => e_in.read_data1,
shift => e_in.read_data2(6 downto 0),
rs => c_in,
ra => a_in,
shift => b_in(6 downto 0),
insn => e_in.insn,
is_32bit => e_in.is_32bit,
right_shift => right_shift,
@ -124,8 +129,8 @@ begin

logical_0: entity work.logical
port map (
rs => e_in.read_data3,
rb => e_in.read_data2,
rs => c_in,
rb => b_in,
op => e_in.insn_type,
invert_in => e_in.invert_a,
invert_out => e_in.invert_out,
@ -137,7 +142,7 @@ begin

countzero_0: entity work.zero_counter
port map (
rs => e_in.read_data3,
rs => c_in,
count_right => e_in.insn(10),
is_32bit => e_in.is_32bit,
result => countzero_result
@ -158,6 +163,10 @@ begin
d_out => divider_to_x
);

a_in <= r.e.write_data when EX1_BYPASS and e_in.bypass_data1 = '1' else e_in.read_data1;
b_in <= r.e.write_data when EX1_BYPASS and e_in.bypass_data2 = '1' else e_in.read_data2;
c_in <= r.e.write_data when EX1_BYPASS and e_in.bypass_data3 = '1' else e_in.read_data3;

execute1_0: process(clk)
begin
if rising_edge(clk) then
@ -256,21 +265,21 @@ begin

if e_in.is_32bit = '1' then
if e_in.is_signed = '1' then
x_to_multiply.data1 <= (others => e_in.read_data1(31));
x_to_multiply.data1(31 downto 0) <= e_in.read_data1(31 downto 0);
x_to_multiply.data2 <= (others => e_in.read_data2(31));
x_to_multiply.data2(31 downto 0) <= e_in.read_data2(31 downto 0);
x_to_multiply.data1 <= (others => a_in(31));
x_to_multiply.data1(31 downto 0) <= a_in(31 downto 0);
x_to_multiply.data2 <= (others => b_in(31));
x_to_multiply.data2(31 downto 0) <= b_in(31 downto 0);
else
x_to_multiply.data1 <= '0' & x"00000000" & e_in.read_data1(31 downto 0);
x_to_multiply.data2 <= '0' & x"00000000" & e_in.read_data2(31 downto 0);
x_to_multiply.data1 <= '0' & x"00000000" & a_in(31 downto 0);
x_to_multiply.data2 <= '0' & x"00000000" & b_in(31 downto 0);
end if;
else
if e_in.is_signed = '1' then
x_to_multiply.data1 <= e_in.read_data1(63) & e_in.read_data1;
x_to_multiply.data2 <= e_in.read_data2(63) & e_in.read_data2;
x_to_multiply.data1 <= a_in(63) & a_in;
x_to_multiply.data2 <= b_in(63) & b_in;
else
x_to_multiply.data1 <= '0' & e_in.read_data1;
x_to_multiply.data2 <= '0' & e_in.read_data2;
x_to_multiply.data1 <= '0' & a_in;
x_to_multiply.data2 <= '0' & b_in;
end if;
end if;

@ -279,23 +288,23 @@ begin
sign2 := '0';
if e_in.is_signed = '1' then
if e_in.is_32bit = '1' then
sign1 := e_in.read_data1(31);
sign2 := e_in.read_data2(31);
sign1 := a_in(31);
sign2 := b_in(31);
else
sign1 := e_in.read_data1(63);
sign2 := e_in.read_data2(63);
sign1 := a_in(63);
sign2 := b_in(63);
end if;
end if;
-- take absolute values
if sign1 = '0' then
abs1 := signed(e_in.read_data1);
abs1 := signed(a_in);
else
abs1 := - signed(e_in.read_data1);
abs1 := - signed(a_in);
end if;
if sign2 = '0' then
abs2 := signed(e_in.read_data2);
abs2 := signed(b_in);
else
abs2 := - signed(e_in.read_data2);
abs2 := - signed(b_in);
end if;

x_to_divider <= Execute1ToDividerInit;
@ -358,14 +367,14 @@ begin
-- Do nothing
when OP_ADD | OP_CMP =>
if e_in.invert_a = '0' then
a_inv := e_in.read_data1;
a_inv := a_in;
else
a_inv := not e_in.read_data1;
a_inv := not a_in;
end if;
result_with_carry := ppc_adde(a_inv, e_in.read_data2,
result_with_carry := ppc_adde(a_inv, b_in,
decode_input_carry(e_in.input_carry, v.e.xerc));
result := result_with_carry(63 downto 0);
carry_32 := result(32) xor a_inv(32) xor e_in.read_data2(32);
carry_32 := result(32) xor a_inv(32) xor b_in(32);
carry_64 := result_with_carry(64);
if e_in.insn_type = OP_ADD then
if e_in.output_carry = '1' then
@ -373,8 +382,8 @@ begin
end if;
if e_in.oe = '1' then
set_ov(v.e,
calc_ov(a_inv(63), e_in.read_data2(63), carry_64, result_with_carry(63)),
calc_ov(a_inv(31), e_in.read_data2(31), carry_32, result_with_carry(31)));
calc_ov(a_inv(63), b_in(63), carry_64, result_with_carry(63)),
calc_ov(a_inv(31), b_in(31), carry_32, result_with_carry(31)));
end if;
result_en := '1';
else
@ -385,20 +394,20 @@ begin
v.e.write_cr_enable := '1';
crnum := to_integer(unsigned(bf));
v.e.write_cr_mask := num_to_fxm(crnum);
zerolo := not (or (e_in.read_data1(31 downto 0) xor e_in.read_data2(31 downto 0)));
zerohi := not (or (e_in.read_data1(63 downto 32) xor e_in.read_data2(63 downto 32)));
zerolo := not (or (a_in(31 downto 0) xor b_in(31 downto 0)));
zerohi := not (or (a_in(63 downto 32) xor b_in(63 downto 32)));
if zerolo = '1' and (l = '0' or zerohi = '1') then
-- values are equal
newcrf := "001" & v.e.xerc.so;
else
if l = '1' then
-- 64-bit comparison
msb_a := e_in.read_data1(63);
msb_b := e_in.read_data2(63);
msb_a := a_in(63);
msb_b := b_in(63);
else
-- 32-bit comparison
msb_a := e_in.read_data1(31);
msb_b := e_in.read_data2(31);
msb_a := a_in(31);
msb_b := b_in(31);
end if;
if msb_a /= msb_b then
-- Subtraction might overflow, but
@ -424,25 +433,25 @@ begin
when OP_B =>
f_out.redirect <= '1';
if (insn_aa(e_in.insn)) then
f_out.redirect_nia <= std_ulogic_vector(signed(e_in.read_data2));
f_out.redirect_nia <= std_ulogic_vector(signed(b_in));
else
f_out.redirect_nia <= std_ulogic_vector(signed(e_in.nia) + signed(e_in.read_data2));
f_out.redirect_nia <= std_ulogic_vector(signed(e_in.nia) + signed(b_in));
end if;
when OP_BC =>
-- read_data1 is CTR
bo := insn_bo(e_in.insn);
bi := insn_bi(e_in.insn);
if bo(4-2) = '0' then
result := std_ulogic_vector(unsigned(e_in.read_data1) - 1);
result := std_ulogic_vector(unsigned(a_in) - 1);
result_en := '1';
v.e.write_reg := fast_spr_num(SPR_CTR);
end if;
if ppc_bc_taken(bo, bi, e_in.cr, e_in.read_data1) = 1 then
if ppc_bc_taken(bo, bi, e_in.cr, a_in) = 1 then
f_out.redirect <= '1';
if (insn_aa(e_in.insn)) then
f_out.redirect_nia <= std_ulogic_vector(signed(e_in.read_data2));
f_out.redirect_nia <= std_ulogic_vector(signed(b_in));
else
f_out.redirect_nia <= std_ulogic_vector(signed(e_in.nia) + signed(e_in.read_data2));
f_out.redirect_nia <= std_ulogic_vector(signed(e_in.nia) + signed(b_in));
end if;
end if;
when OP_BCREG =>
@ -451,40 +460,40 @@ begin
bo := insn_bo(e_in.insn);
bi := insn_bi(e_in.insn);
if bo(4-2) = '0' and e_in.insn(10) = '0' then
result := std_ulogic_vector(unsigned(e_in.read_data1) - 1);
result := std_ulogic_vector(unsigned(a_in) - 1);
result_en := '1';
v.e.write_reg := fast_spr_num(SPR_CTR);
end if;
if ppc_bc_taken(bo, bi, e_in.cr, e_in.read_data1) = 1 then
if ppc_bc_taken(bo, bi, e_in.cr, a_in) = 1 then
f_out.redirect <= '1';
f_out.redirect_nia <= e_in.read_data2(63 downto 2) & "00";
f_out.redirect_nia <= b_in(63 downto 2) & "00";
end if;
when OP_CMPB =>
result := ppc_cmpb(e_in.read_data3, e_in.read_data2);
result := ppc_cmpb(c_in, b_in);
result_en := '1';
when OP_CNTZ =>
result := countzero_result;
result_en := '1';
when OP_EXTS =>
-- note data_len is a 1-hot encoding
negative := (e_in.data_len(0) and e_in.read_data3(7)) or
(e_in.data_len(1) and e_in.read_data3(15)) or
(e_in.data_len(2) and e_in.read_data3(31));
negative := (e_in.data_len(0) and c_in(7)) or
(e_in.data_len(1) and c_in(15)) or
(e_in.data_len(2) and c_in(31));
result := (others => negative);
if e_in.data_len(2) = '1' then
result(31 downto 16) := e_in.read_data3(31 downto 16);
result(31 downto 16) := c_in(31 downto 16);
end if;
if e_in.data_len(2) = '1' or e_in.data_len(1) = '1' then
result(15 downto 8) := e_in.read_data3(15 downto 8);
result(15 downto 8) := c_in(15 downto 8);
end if;
result(7 downto 0) := e_in.read_data3(7 downto 0);
result(7 downto 0) := c_in(7 downto 0);
result_en := '1';
when OP_ISEL =>
crbit := to_integer(unsigned(insn_bc(e_in.insn)));
if e_in.cr(31-crbit) = '1' then
result := e_in.read_data1;
result := a_in;
else
result := e_in.read_data2;
result := b_in;
end if;
result_en := '1';
when OP_MCRF =>
@ -549,7 +558,7 @@ begin
end if;
when OP_MFSPR =>
if is_fast_spr(e_in.read_reg1) then
result := e_in.read_data1;
result := a_in;
if decode_spr_num(e_in.insn) = SPR_XER then
-- bits 0:31 and 35:43 are treated as reserved and return 0s when read using mfxer
result(63 downto 32) := (others => '0');
@ -596,19 +605,19 @@ begin
crnum := fxm_to_num(insn_fxm(e_in.insn));
v.e.write_cr_mask := num_to_fxm(crnum);
end if;
v.e.write_cr_data := e_in.read_data3(31 downto 0);
v.e.write_cr_data := c_in(31 downto 0);
when OP_MTSPR =>
report "MTSPR to SPR " & integer'image(decode_spr_num(e_in.insn)) &
"=" & to_hstring(e_in.read_data3);
"=" & to_hstring(c_in);
if is_fast_spr(e_in.write_reg) then
result := e_in.read_data3;
result := c_in;
result_en := '1';
if decode_spr_num(e_in.insn) = SPR_XER then
v.e.xerc.so := e_in.read_data3(63-32);
v.e.xerc.ov := e_in.read_data3(63-33);
v.e.xerc.ca := e_in.read_data3(63-34);
v.e.xerc.ov32 := e_in.read_data3(63-44);
v.e.xerc.ca32 := e_in.read_data3(63-45);
v.e.xerc.so := c_in(63-32);
v.e.xerc.ov := c_in(63-33);
v.e.xerc.ca := c_in(63-34);
v.e.xerc.ov32 := c_in(63-44);
v.e.xerc.ca32 := c_in(63-45);
v.e.write_xerc_enable := '1';
end if;
else

50
gpr_hazard.vhdl
Unescape Escape View File

@ -12,18 +12,21 @@ entity gpr_hazard is

gpr_write_valid_in : in std_ulogic;
gpr_write_in : in std_ulogic_vector(5 downto 0);
bypass_avail : in std_ulogic;
gpr_read_valid_in : in std_ulogic;
gpr_read_in : in std_ulogic_vector(5 downto 0);

stall_out : out std_ulogic
stall_out : out std_ulogic;
use_bypass : out std_ulogic
);
end entity gpr_hazard;
architecture behaviour of gpr_hazard is
type pipeline_entry_type is record
valid : std_ulogic;
bypass : std_ulogic;
gpr : std_ulogic_vector(5 downto 0);
end record;
constant pipeline_entry_init : pipeline_entry_type := (valid => '0', gpr => (others => '0'));
constant pipeline_entry_init : pipeline_entry_type := (valid => '0', bypass => '0', gpr => (others => '0'));

type pipeline_t is array(0 to PIPELINE_DEPTH-1) of pipeline_entry_type;
constant pipeline_t_init : pipeline_t := (others => pipeline_entry_init);
@ -33,10 +36,8 @@ begin
gpr_hazard0: process(clk)
begin
if rising_edge(clk) then
if stall_in = '0' then
r <= rin;
end if;
end if;
end process;

gpr_hazard1: process(all)
@ -45,22 +46,49 @@ begin
v := r;

stall_out <= '0';
loop_0: for i in 0 to PIPELINE_DEPTH-1 loop
if ((r(i).valid = gpr_read_valid_in) and r(i).gpr = gpr_read_in) then
use_bypass <= '0';
if gpr_read_valid_in = '1' then
if r(0).valid = '1' and r(0).gpr = gpr_read_in then
if r(0).bypass = '1' and stall_in = '0' then
use_bypass <= '1';
else
stall_out <= '1';
end if;
end if;
loop_0: for i in 1 to PIPELINE_DEPTH-1 loop
if r(i).valid = '1' and r(i).gpr = gpr_read_in then
if r(i).bypass = '1' then
use_bypass <= '1';
else
stall_out <= '1';
end if;
end if;
end loop;
end if;

if stall_in = '0' then
v(0).valid := gpr_write_valid_in;
v(0).bypass := bypass_avail;
v(0).gpr := gpr_write_in;
loop_1: for i in 0 to PIPELINE_DEPTH-2 loop
loop_1: for i in 1 to PIPELINE_DEPTH-1 loop
-- propagate to next slot
v(i+1) := r(i);
v(i).valid := r(i-1).valid;
v(i).bypass := r(i-1).bypass;
v(i).gpr := r(i-1).gpr;
end loop;

-- asynchronous output
if gpr_read_valid_in = '0' then
stall_out <= '0';
else
-- stage 0 stalled, so stage 1 becomes empty
loop_1b: for i in 1 to PIPELINE_DEPTH-1 loop
-- propagate to next slot
if i = 1 then
v(i).valid := '0';
else
v(i).valid := r(i-1).valid;
v(i).bypass := r(i-1).bypass;
v(i).gpr := r(i-1).gpr;
end if;
end loop;
end if;

-- update registers

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