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dfflegalize: Add special support for const-D latches.

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Those can be created by `opt_dff` when optimizing `$adff` with const
clock, or with D == Q.  Make dfflegalize do the opposite transform
when such dlatches would be otherwise unimplementable.
This commit is contained in:
Marcelina Kościelnicka 2020-07-06 22:52:05 +02:00
parent 000fd08198
commit e9c2c1b717
2 changed files with 71 additions and 0 deletions
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18
passes/techmap/dfflegalize.cc
View file

@ -659,6 +659,24 @@ flip_dqisr:;
// This init value is not supported at all...
if (supported_dlatch & flip_initmask(initmask))
goto flip_dqi;
if ((sig_d == State::S0 && (supported_adff0 & initmask)) ||
(sig_d == State::S1 && (supported_adff1 & initmask)) ||
(sig_d == State::S0 && (supported_adff1 & flip_initmask(initmask))) ||
(sig_d == State::S1 && (supported_adff0 & flip_initmask(initmask)))
) {
// Special case: const-D dlatch can be converted into adff with const clock.
ff_type = (sig_d == State::S0) ? FF_ADFF0 : FF_ADFF1;
if (ff_neg & NEG_E) {
ff_neg &= ~NEG_E;
ff_neg |= NEG_R;
}
sig_r = sig_e;
sig_d = State::Sx;
sig_c = State::S1;
continue;
}
if (!supported_dlatch)
reason = "dlatch are not supported";
else

53
tests/techmap/dfflegalize_dlatch_const.ys Normal file
View file

@ -0,0 +1,53 @@
read_verilog -icells <<EOT
module dlatch(input E, D, (* init = 8'hf0 *) output [7:0] Q);
$_DLATCH_P_ ff0 (.E(E), .D(1'b0), .Q(Q[0]));
$_DLATCH_N_ ff1 (.E(E), .D(1'b0), .Q(Q[1]));
$_DLATCH_P_ ff2 (.E(E), .D(1'b1), .Q(Q[2]));
$_DLATCH_N_ ff3 (.E(E), .D(1'b1), .Q(Q[3]));
$_DLATCH_P_ ff4 (.E(E), .D(1'b0), .Q(Q[4]));
$_DLATCH_N_ ff5 (.E(E), .D(1'b0), .Q(Q[5]));
$_DLATCH_P_ ff6 (.E(E), .D(1'b1), .Q(Q[6]));
$_DLATCH_N_ ff7 (.E(E), .D(1'b1), .Q(Q[7]));
endmodule
EOT
design -save orig
equiv_opt -assert -multiclock -map +/simcells.v dfflegalize -cell $_DFF_PP0_ 01
equiv_opt -assert -multiclock -map +/simcells.v dfflegalize -cell $_DFF_PP?_ 0
equiv_opt -assert -multiclock -map +/simcells.v dfflegalize -cell $_DFFSRE_PPPP_ 0
equiv_opt -assert -multiclock -map +/simcells.v dfflegalize -cell $_DFFSRE_PPPP_ 1
# Convert everything to ADFFs.
design -load orig
dfflegalize -cell $_DFF_PP0_ 01
select -assert-count 12 t:$_NOT_
select -assert-count 8 t:$_DFF_PP0_
select -assert-none t:$_DFF_PP0_ t:$_NOT_ %% %n t:* %i
design -load orig
dfflegalize -cell $_DFF_PP?_ 0
select -assert-count 12 t:$_NOT_
select -assert-count 4 t:$_DFF_PP0_
select -assert-count 4 t:$_DFF_PP1_
select -assert-none t:$_DFF_PP0_ t:$_DFF_PP1_ t:$_NOT_ %% %n t:* %i
# Convert everything to DFFSREs.
design -load orig
dfflegalize -cell $_DFFSRE_PPPP_ 0
select -assert-count 12 t:$_NOT_
select -assert-count 8 t:$_DFFSRE_PPPP_
select -assert-none t:$_DFFSRE_PPPP_ t:$_NOT_ %% %n t:* %i
design -load orig
dfflegalize -cell $_DFFSRE_PPPP_ 1
select -assert-count 12 t:$_NOT_
select -assert-count 8 t:$_DFFSRE_PPPP_
select -assert-none t:$_DFFSRE_PPPP_ t:$_NOT_ %% %n t:* %i