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Merge pull request #4971 from Anhijkt/pow-optimization

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opt_expr: optimize pow of 2 cells
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George Rennie 2025-04-03 14:34:36 +02:00 • committed by GitHub
commit 63b3ce0c77
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31
passes/opt/opt_expr.cc
View file

@ -1690,7 +1690,38 @@ skip_identity:
else if (inA == inB)
ACTION_DO(ID::Y, cell->getPort(ID::A));
}
if (cell->type == ID($pow) && cell->getPort(ID::A).is_fully_const() && !cell->parameters[ID::B_SIGNED].as_bool()) {
SigSpec sig_a = assign_map(cell->getPort(ID::A));
SigSpec sig_y = assign_map(cell->getPort(ID::Y));
int y_size = GetSize(sig_y);
int bit_idx;
const auto onehot = sig_a.is_onehot(&bit_idx);
if (onehot) {
if (bit_idx == 1) {
log_debug("Replacing pow cell `%s' in module `%s' with left-shift\n",
cell->name.c_str(), module->name.c_str());
cell->type = ID($shl);
cell->parameters[ID::A_WIDTH] = 1;
cell->setPort(ID::A, Const(State::S1, 1));
}
else {
log_debug("Replacing pow cell `%s' in module `%s' with multiply and left-shift\n",
cell->name.c_str(), module->name.c_str());
cell->type = ID($mul);
cell->parameters[ID::A_SIGNED] = 0;
cell->setPort(ID::A, Const(bit_idx, cell->parameters[ID::A_WIDTH].as_int()));
SigSpec y_wire = module->addWire(NEW_ID, y_size);
cell->setPort(ID::Y, y_wire);
module->addShl(NEW_ID, Const(State::S1, 1), y_wire, sig_y);
}
did_something = true;
goto next_cell;
}
}
if (!keepdc && cell->type == ID($mul))
{
bool a_signed = cell->parameters[ID::A_SIGNED].as_bool();

89
tests/opt/opt_pow.ys Normal file
View file

@ -0,0 +1,89 @@
# Default power of two
design -reset
read_rtlil << EOT
autoidx 3
attribute \cells_not_processed 1
attribute \src "<stdin>:1.1-3.10"
module \top
attribute \src "<stdin>:2.17-2.20"
wire width 32 $add$<stdin>:2$1_Y
attribute \src "<stdin>:2.12-2.21"
wire width 32 signed $pow$<stdin>:2$2_Y
attribute \src "<stdin>:1.29-1.30"
wire width 15 input 1 \a
attribute \src "<stdin>:1.51-1.52"
wire width 32 output 2 \b
attribute \src "<stdin>:2.17-2.20"
cell $add $add$<stdin>:2$1
parameter \A_SIGNED 0
parameter \A_WIDTH 15
parameter \B_SIGNED 0
parameter \B_WIDTH 32
parameter \Y_WIDTH 32
connect \A \a
connect \B 2
connect \Y $add$<stdin>:2$1_Y
end
attribute \src "<stdin>:2.12-2.21"
cell $pow $pow$<stdin>:2$2
parameter \A_SIGNED 0
parameter \A_WIDTH 32
parameter \B_SIGNED 0
parameter \B_WIDTH 32
parameter \Y_WIDTH 32
connect \A 2
connect \B $add$<stdin>:2$1_Y
connect \Y $pow$<stdin>:2$2_Y
end
connect \b $pow$<stdin>:2$2_Y
end
EOT
select -assert-count 1 t:$pow
select -assert-none t:$shl
opt_expr
select -assert-none t:$pow
select -assert-count 1 t:$shl
read_verilog << EOT
module ref(input wire [14:0] a, output wire [31:0] b);
assign b = 1 << (a+2);
endmodule
EOT
equiv_make top ref equiv
select -assert-any -module equiv t:$equiv
equiv_induct
equiv_status -assert
# Other power of 2 value
design -reset
read_verilog <<EOT
module top(input wire [14:0] a, output wire [31:0] b);
assign b = 128**(a+2);
endmodule
EOT
# Check the cell counts have changed correctly
select -assert-count 1 t:$pow
select -assert-none t:$shl
select -assert-none t:$mul
opt_expr
select -assert-none t:$pow
select -assert-count 1 t:$shl
select -assert-count 1 t:$mul
read_verilog <<EOT
module ref(input wire [14:0] a, output wire [31:0] b);
assign b = 1 << (7 * (a+2));
endmodule
EOT
equiv_make top ref equiv
select -assert-any -module equiv t:$equiv
equiv_induct
equiv_status -assert