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Merge pull request #5886 from YosysHQ/nella/fix-signedness-5745

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Fix  `chparam` values are unsigned when using read_verilog frontend
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nella 2026-06-18 16:50:22 +00:00 • committed by GitHub
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# Issue #5745: chparam values are unsigned when using read_verilog frontend
#
# When chparam overrides a parameter value, the signed attribute is lost,
# causing signed comparisons to silently use unsigned logic.
#
# m = -32 (signed 9-bit), p2 = 11. Correct signed semantics: -32 < 11, so k = 1.
# Bug: chparam strips the signed attribute from p2. The $lt cell gets A_SIGNED=0,
# B_SIGNED=0, so the comparison treats m as unsigned (480 > 11), giving k = 0.
read_verilog <<EOT
module mod #(parameter p2=11) (output k);
wire signed [8:0] m = -32;
assign k = m < p2;
endmodule
EOT
chparam -set p2 11
hierarchy -top mod
sat -prove k 1 -verify