Add proper reports to bugs

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+# Yosys aborts with exception in peephole optimizers pass
+
+[ [Issue 993](https://github.com/YosysHQ/yosys/issues/993) ]
+
+Yosys aborts with a `vector::_M_range_check` exception in the peephole optimizers pass (`PEEPOPT pass`). This happens with the verilog code below, which I have reduced as much as possible into an MCVE.
+
+```verilog
+module top(y, clk, wire1);
+   output wire [1:0] y;
+   input wire        clk;
+   input wire [1:0]  wire1;
+   reg [1:0]         reg1 = 0;
+   reg [1:0]         reg2 = 0;
+   always @(posedge clk) begin
+      reg1 <= wire1 == 1;
+   end
+   always @(posedge clk) begin
+      reg2 <= 1 >> reg1[1:1];
+   end
+   assign y = reg2;
+endmodule
+```
+
+## Steps to reproduce the issue
+
+Yosys version that this was tested with: `Yosys 0.8+411 (git sha1 70d0f389, clang 8.0.0 -fPIC -Os)`, which is the current master.
+
+The following command was used to synthesise the design:
+
+```
+yosys -p 'read -formal rtl.v; synth; write_verilog rtl_yosys.v'
+```
+
+## Expected behavior
+
+Synthesis without any exceptions.
+
+```
+=== top ===
+
+   Number of wires:                  4
+   Number of wire bits:              8
+   Number of public wires:           4
+   Number of public wire bits:       8
+   Number of memories:               0
+   Number of memory bits:            0
+   Number of processes:              0
+   Number of cells:                  1
+     $_ORNOT_                        1
+
+2.27. Executing CHECK pass (checking for obvious problems).
+checking module top..
+found and reported 0 problems.
+
+3. Executing Verilog backend.
+Dumping module `\top'.
+```
+
+## Actual behavior
+
+Yosys aborts with a `vector::_M_range_check` exception.
+
+```
+2.7. Executing WREDUCE pass (reducing word size of cells).
+Removed top 1 bits (of 2) from port B of cell top.$eq$rtl.v:7$2 ($eq).
+Removed cell top.$eq$rtl.v:7$2 ($eq).
+Removed top 30 bits (of 32) from port A of cell top.$shr$rtl.v:10$4 ($shr).
+
+2.8. Executing PEEPOPT pass (run peephole optimizers).
+terminate called after throwing an instance of 'std::out_of_range'
+  what():  vector::_M_range_check: __n (which is 18446744073709551615) >= this->size() (which is 0)
+zsh: abort (core dumped)  yosys -p 'read -formal rtl.v; synth; write_verilog rtl_yosys.v'
+```