Icarus confused about signed/unsigned in strange ?: example

[cliffordwolf]

The following module should set the output to constant 0, because the 4'b0 makes the whole expression unsigned.

module issue_032(y);
  wire signed [3:0] a = -5;
  wire signed [3:0] b =  0;
  output y;
  assign y = (1 ? a : 4'b0) < (1 ? b : b); 
  initial #1 $display("%b", y);
endmodule

But Icarus Verilog (git 3e41a93) assigns 1 instead. Interestingly the bug goes away if the (1 ? b : b) is replaced by b.

[martinwhitaker]

I've pushed a fix for this to the git master branch. The compiler was correctly determining that the expression was unsigned, but losing this information during optimisation of the ternary expressions.