Vivado hangs forever on modulo with undefined (X) value

OPEN: last verified in Vivado 2018.3

Consider the following test case:

module issue_059(a, y);
    input [2:0] a;
    output [3:0] y;
    assign y = a % 1'bx;

Vivado simply hangs forever trying to synthesize this design.

Vivado produces a "CRITICAL WARNING: [Synth 8-5821] Potential divide by zero" message when modulo (%) is replaced with divide (/). But when Vivado is run with set_msg_config -id {Synth 8-5821} -new_severity {WARNING} then the case using division also hangs forever.

2019-01-15 Initial description of bug.

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