Add proper reports to bugs

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+# Vivado 2018.3 synthesis crash
+
+[ [Vivado forum 981136](https://forums.xilinx.com/t5/Synthesis/Vivado-2018-3-synthesis-crash/td-p/981136) ]
+
+Vivado 2018.3 crashes with the following Verilog code.
+
+```verilog
+module top  (y, clk, wire0);
+   output y;
+   input  clk;
+   input [1:0] wire0;
+   reg [1:0]   reg1 = 0, reg0 = 0, reg2 = 0,
+               reg3 = 0, reg4 = 0;
+   reg signed [1:0] reg5 = 0;
+   wire [1:0]       wire1;
+   assign y = reg1;
+   assign wire1 = reg4;
+   always @(posedge clk)
+     if (reg4)
+       begin
+          if (wire0)
+            reg3 <= 1;
+          reg2 <= 1;
+       end
+   always @(posedge clk)
+     if (reg3) begin
+        reg5 <= reg2[0:0];
+        if (reg0)
+          reg1 <= reg5;
+        if (reg2[0:0])
+          reg0 <= 1;
+     end
+endmodule
+```
+
+It results in the error shown below.
+
+```
+****** Vivado v2018.3 (64-bit)
+  **** SW Build 2405991 on Thu Dec  6 23:36:41 MST 2018
+  **** IP Build 2404404 on Fri Dec  7 01:43:56 MST 2018
+    ** Copyright 1986-2018 Xilinx, Inc. All Rights Reserved.
+
+source vivado_top.tcl
+# set_msg_config -id {Synth 8-5821} -new_severity {WARNING}
+# read_verilog rtl.v
+# synth_design -part xc7k70t -top top
+Command: synth_design -part xc7k70t -top top
+Starting synth_design
+Attempting to get a license for feature 'Synthesis' and/or device 'xc7k70t'
+INFO: [Common 17-349] Got license for feature 'Synthesis' and/or device 'xc7k70t'
+INFO: Launching helper process for spawning children vivado processes
+INFO: Helper process launched with PID 10415
+---------------------------------------------------------------------------------
+Starting Synthesize : Time (s): cpu = 00:00:02 ; elapsed = 00:00:02 . Memory (MB): peak = 1349.855 ; gain = 0.000 ; free physical = 1545 ; free virtual = 5134
+---------------------------------------------------------------------------------
+INFO: [Synth 8-6157] synthesizing module 'top' [/home/user/project/rtl.v:1]
+Abnormal program termination (11)
+Please check '/home/user/project/hs_err_pid10402.log' for details
+```