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opt_expr: Fix #4590

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If all the (non-select) inputs of a `$_MUX{4,8,16}_` are undefined, replace it, just like we do for `$mux` and `$_MUX_`.
Add `tests/opt/opt_expr_mux_undef.ys` to verify this.

This doesn't do any const folding on the wide muxes, or shrinking to less wide muxes.  It only handles the case where all inputs are 'x and the mux can be completely removed.
This commit is contained in:
Krystine Sherwin 2025-04-04 12:25:31 +13:00
parent 63b3ce0c77
commit 406b400458
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2 changed files with 304 additions and 0 deletions
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14
passes/opt/opt_expr.cc
View file

@ -1573,6 +1573,20 @@ skip_identity:
}
}
if (mux_undef && cell->type.in(ID($_MUX4_), ID($_MUX8_), ID($_MUX16_))) {
int num_inputs = 4;
if (cell->type == ID($_MUX8_)) num_inputs = 8;
if (cell->type == ID($_MUX16_)) num_inputs = 16;
int undef_inputs = 0;
for (auto &conn : cell->connections())
if (!conn.first.in(ID::S, ID::T, ID::U, ID::V, ID::Y))
undef_inputs += conn.second.is_fully_undef();
if (undef_inputs == num_inputs) {
replace_cell(assign_map, module, cell, "mux_undef", ID::Y, cell->getPort(ID::A));
goto next_cell;
}
}
#define FOLD_1ARG_CELL(_t) \
if (cell->type == ID($##_t)) { \
RTLIL::SigSpec a = cell->getPort(ID::A); \

290
tests/opt/opt_expr_mux_undef.ys Normal file
View file

@ -0,0 +1,290 @@
read_rtlil <<EOT
module \uut
wire output 1 \out
wire input 2 width 16 \in
wire input 3 width 4 \sel
cell $_MUX16_ \mux
connect \A \in [0]
connect \B \in [1]
connect \C \in [2]
connect \D \in [3]
connect \E \in [4]
connect \F \in [5]
connect \G \in [6]
connect \H \in [7]
connect \I \in [8]
connect \J \in [9]
connect \K \in [10]
connect \L \in [11]
connect \M \in [12]
connect \N \in [13]
connect \O \in [14]
connect \P \in [15]
connect \S \sel [0]
connect \T \sel [1]
connect \U \sel [2]
connect \V \sel [3]
connect \Y \out
end
end
EOT
##########
# all undef
# no mux
# output undef
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
cell $mux \mux
parameter \WIDTH 1
connect \A 1'x
connect \B 1'x
connect \S 1'x
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$mux
select -assert-count 1 o:out %ci*
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
cell $_MUX_ \mux
connect \A 1'x
connect \B 1'x
connect \S 1'x
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX_
select -assert-count 1 o:out %ci*
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
cell $_MUX4_ \mux
connect \A 1'x
connect \B 1'x
connect \C 1'x
connect \D 1'x
connect \S 1'x
connect \T 1'x
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX4_
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
cell $_MUX8_ \mux
connect \A 1'x
connect \B 1'x
connect \C 1'x
connect \D 1'x
connect \E 1'x
connect \F 1'x
connect \G 1'x
connect \H 1'x
connect \S 1'x
connect \T 1'x
connect \U 1'x
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX8_
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
cell $_MUX16_ \mux
connect \A 1'x
connect \B 1'x
connect \C 1'x
connect \D 1'x
connect \E 1'x
connect \F 1'x
connect \G 1'x
connect \H 1'x
connect \I 1'x
connect \J 1'x
connect \K 1'x
connect \L 1'x
connect \M 1'x
connect \N 1'x
connect \O 1'x
connect \P 1'x
connect \S 1'x
connect \T 1'x
connect \U 1'x
connect \V 1'x
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX16_
##########
# a and b undef
# no mux
# output undef
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
wire input 3 \sel
cell $mux \mux
parameter \WIDTH 1
connect \A 1'x
connect \B 1'x
connect \S \sel
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$mux
select -assert-count 1 o:out %ci*
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
wire input 3 \sel
cell $_MUX_ \mux
connect \A 1'x
connect \B 1'x
connect \S \sel
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX_
select -assert-count 1 o:out %ci*
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
wire input 3 width 2 \sel
cell $_MUX4_ \mux
connect \A 1'x
connect \B 1'x
connect \C 1'x
connect \D 1'x
connect \S \sel [0]
connect \T \sel [1]
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX4_
select -assert-count 1 o:out %ci*
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
wire input 3 width 3 \sel
cell $_MUX8_ \mux
connect \A 1'x
connect \B 1'x
connect \C 1'x
connect \D 1'x
connect \E 1'x
connect \F 1'x
connect \G 1'x
connect \H 1'x
connect \S \sel [0]
connect \T \sel [1]
connect \U \sel [2]
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX8_
select -assert-count 1 o:out %ci*
##
design -reset
read_rtlil <<EOT
module \uut
wire output 1 \out
wire input 3 width 4 \sel
cell $_MUX16_ \mux
connect \A 1'x
connect \B 1'x
connect \C 1'x
connect \D 1'x
connect \E 1'x
connect \F 1'x
connect \G 1'x
connect \H 1'x
connect \I 1'x
connect \J 1'x
connect \K 1'x
connect \L 1'x
connect \M 1'x
connect \N 1'x
connect \O 1'x
connect \P 1'x
connect \S \sel [0]
connect \T \sel [1]
connect \U \sel [2]
connect \V \sel [3]
connect \Y \out
end
end
EOT
opt_expr -mux_undef
select -assert-none t:$_MUX16_
select -assert-count 1 o:out %ci*
##########