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Merge pull request #771 from whitequark/techmap_cmp2lut

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cmp2lut: new techmap pass
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Clifford Wolf 2019-01-02 15:43:10 +01:00 • committed by GitHub
commit 00330c741a
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5 changed files with 139 additions and 3 deletions
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2
techlibs/common/Makefile.inc
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@ -26,5 +26,5 @@ $(eval $(call add_share_file,share,techlibs/common/pmux2mux.v))
$(eval $(call add_share_file,share,techlibs/common/adff2dff.v))
$(eval $(call add_share_file,share,techlibs/common/dff2ff.v))
$(eval $(call add_share_file,share,techlibs/common/gate2lut.v))
$(eval $(call add_share_file,share,techlibs/common/cmp2lut.v))
$(eval $(call add_share_file,share,techlibs/common/cells.lib))

105
techlibs/common/cmp2lut.v Normal file
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@ -0,0 +1,105 @@
// Certain arithmetic operations between a signal of width n and a constant can be directly mapped
// to a single k-LUT (where n <= k). This is preferable to normal alumacc techmapping process
// because for many targets, arithmetic techmapping creates hard logic (such as carry cells) which often
// cannot be optimized further.
//
// TODO: Currently, only comparisons with 1-bit output are mapped. Potentially, all arithmetic cells
// with n <= k inputs should be techmapped in this way, because this shortens the critical path
// from n to 1 by avoiding carry chains.
(* techmap_celltype = "$eq $ne $lt $le $gt $ge" *)
module _90_lut_cmp_ (A, B, Y);
parameter A_SIGNED = 0;
parameter B_SIGNED = 0;
parameter A_WIDTH = 0;
parameter B_WIDTH = 0;
parameter Y_WIDTH = 0;
input [A_WIDTH-1:0] A;
input [B_WIDTH-1:0] B;
output [Y_WIDTH-1:0] Y;
parameter _TECHMAP_CELLTYPE_ = "";
parameter _TECHMAP_CONSTMSK_A_ = 0;
parameter _TECHMAP_CONSTVAL_A_ = 0;
parameter _TECHMAP_CONSTMSK_B_ = 0;
parameter _TECHMAP_CONSTVAL_B_ = 0;
function automatic integer gen_lut;
input integer width;
input integer operation;
input integer swap;
input integer sign;
input integer operand;
integer n, i_var, i_cst, lhs, rhs, o_bit;
begin
gen_lut = width'b0;
for (n = 0; n < (1 << width); n++) begin
if (sign)
i_var = n[width-1:0];
else
i_var = n;
i_cst = operand;
if (swap) begin
lhs = i_cst;
rhs = i_var;
end else begin
lhs = i_var;
rhs = i_cst;
end
if (operation == 0)
o_bit = (lhs < rhs);
if (operation == 1)
o_bit = (lhs <= rhs);
if (operation == 2)
o_bit = (lhs > rhs);
if (operation == 3)
o_bit = (lhs >= rhs);
if (operation == 4)
o_bit = (lhs == rhs);
if (operation == 5)
o_bit = (lhs != rhs);
gen_lut = gen_lut | (o_bit << n);
end
end
endfunction
generate
if (_TECHMAP_CELLTYPE_ == "$lt")
localparam operation = 0;
if (_TECHMAP_CELLTYPE_ == "$le")
localparam operation = 1;
if (_TECHMAP_CELLTYPE_ == "$gt")
localparam operation = 2;
if (_TECHMAP_CELLTYPE_ == "$ge")
localparam operation = 3;
if (_TECHMAP_CELLTYPE_ == "$eq")
localparam operation = 4;
if (_TECHMAP_CELLTYPE_ == "$ne")
localparam operation = 5;
if (A_WIDTH > `LUT_WIDTH || B_WIDTH > `LUT_WIDTH || Y_WIDTH != 1)
wire _TECHMAP_FAIL_ = 1;
else if (&_TECHMAP_CONSTMSK_B_)
\$lut #(
.WIDTH(A_WIDTH),
.LUT({ gen_lut(A_WIDTH, operation, 0, A_SIGNED && B_SIGNED, _TECHMAP_CONSTVAL_B_) })
) _TECHMAP_REPLACE_ (
.A(A),
.Y(Y)
);
else if (&_TECHMAP_CONSTMSK_A_)
\$lut #(
.WIDTH(B_WIDTH),
.LUT({ gen_lut(B_WIDTH, operation, 1, A_SIGNED && B_SIGNED, _TECHMAP_CONSTVAL_A_) })
) _TECHMAP_REPLACE_ (
.A(B),
.Y(Y)
);
else
wire _TECHMAP_FAIL_ = 1;
endgenerate
endmodule