Invalid optimization of or-reduce with undef bits

OPEN: last verified in Quartus 17.0

Consider the following test case:

module issue_031(a, y);
  input [2:0] a;
  output [2:0] y;
  assign y = { &{a,1'bx}, |{a,1'bx}, ^{a,1'bx} };

Quartus 15.0 sets y to constant 3'b000. But for y[1] only '1' is a valid constant value.

Crosscheck: Vivado 2015.1, XSim 2015.1, Modelsim 10.3d, Icarus Verilog (git 02ee387), and Verilator (git e5af46d) all agree on the correct behavior.

2015-05-15 Reported via Altera mySupport (SR #11146970)
2017-07-01 Still broken in Quartus II 17.0

← Back to VlogHammer Project Page