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mul2dsp: normalize operand order

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Move the operand commute that puts the wider operand on A ahead of the
min-width checks. Checking the min-widths first made an asymmetric rule
(DSP_A_MINWIDTH != DSP_B_MINWIDTH) match only products that already had the
wider operand on A; a product in the other order was rejected before the
normalization.
This commit is contained in:
Johan Olby 2026-07-15 16:21:07 +02:00
parent 9914b6fa25
commit 63457de80e
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GPG key ID: 099308365347DFA9
2 changed files with 46 additions and 12 deletions
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26
techlibs/common/mul2dsp.v
View file

@ -68,6 +68,20 @@ module _80_mul (A, B, Y);
generate
if (0) begin end
// Normalize operand order (wider operand on A) to simplify asymmetric
// rules (DSP_A_MINWIDTH != DSP_B_MINWIDTH) below.
else if (_TECHMAP_CELLTYPE_ == "$mul" && A_WIDTH < B_WIDTH)
\$mul #(
.A_SIGNED(B_SIGNED),
.B_SIGNED(A_SIGNED),
.A_WIDTH(B_WIDTH),
.B_WIDTH(A_WIDTH),
.Y_WIDTH(Y_WIDTH)
) _TECHMAP_REPLACE_ (
.A(B),
.B(A),
.Y(Y)
);
`ifdef DSP_A_MINWIDTH
else if (A_WIDTH < `DSP_A_MINWIDTH)
wire _TECHMAP_FAIL_ = 1;
@ -94,18 +108,6 @@ module _80_mul (A, B, Y);
.Y(Y)
);
`endif
else if (_TECHMAP_CELLTYPE_ == "$mul" && A_WIDTH < B_WIDTH)
\$mul #(
.A_SIGNED(B_SIGNED),
.B_SIGNED(A_SIGNED),
.A_WIDTH(B_WIDTH),
.B_WIDTH(A_WIDTH),
.Y_WIDTH(Y_WIDTH)
) _TECHMAP_REPLACE_ (
.A(B),
.B(A),
.Y(Y)
);
else begin
wire [1023:0] _TECHMAP_DO_ = "proc; clean";

32
tests/techmap/mul2dsp_asymmetric.ys Normal file
View file

@ -0,0 +1,32 @@
# Test operand-order normalization: a 4x13 product with an asymmetric rule
# (A_MIN=10, B_MIN=4) fails in this order (A=4 < A_MIN) but maps to one DSP
# cell once the wide operand is normalized onto A.
read_verilog <<EOF
module top(a, b, y);
input signed [3:0] a;
input signed [12:0] b;
output signed [16:0] y;
assign y = a * b;
endmodule
EOF
read_verilog -lib <<EOF
module \$__MUL18X18 (A, B, Y);
parameter A_SIGNED = 0;
parameter B_SIGNED = 0;
parameter A_WIDTH = 18;
parameter B_WIDTH = 18;
parameter Y_WIDTH = 36;
input [A_WIDTH-1:0] A;
input [B_WIDTH-1:0] B;
output [Y_WIDTH-1:0] Y;
endmodule
EOF
hierarchy -top top
proc
techmap -map +/mul2dsp.v -D DSP_A_MAXWIDTH=18 -D DSP_B_MAXWIDTH=18 -D DSP_A_MINWIDTH=10 -D DSP_B_MINWIDTH=4 -D DSP_NAME=\$__MUL18X18
select -module top
select -assert-count 1 t:\$__MUL18X18