Bambu shift and and bug

Reported	Fixed
Issue	X

The following C code should output 0x100 as b is just shifted to the right by 8. However, in bambu it outputs 0.

./bug.c

static int b = 0x10000;
static volatile short a = 0;

int result() {
  a++;
  b = (b >> 8) & 0x100;
  return b;
}

We can then generate two different files to run the bug with gcc and bambu respectively.

./main_gcc.c

#include "./bug.c"
#include <stdio.h>

int main () {
    int res = result();
    printf("checksum = %08X\n", res);
    return 0;
}

./main_bambu.c

#include "./bug.c"

int main () { return result(); }

For bambu we also need a test bench in verilog to execute the code:

./tb.v

module testbench;
   reg clock, reset, start_port;
   wire done_port;
   wire [31:0] return_port;

   main m(.clock(clock), .reset(reset), .start_port(start_port), .done_port(done_port), .return_port(return_port));

   always #10 clock = ~clock;

   initial begin
      clock = 0;
      reset = 0;
      start_port = 0;
      @(posedge clock) reset = 0;
      @(posedge clock) reset = 1; start_port = 1;
      @(posedge clock) start_port = 0;
   end

   always @(posedge clock)
     if (done_port) begin
        $display("checksum = %h", return_port);
        $finish;
     end

endmodule

Finally, to reproduce the bug, one can run the following commands.

gcc main_gcc.c -o main_gcc
./main_gcc | tee out.gold.txt

checksum = 00000100

bambu main_bambu.c >bambu.log 2>&1
iverilog top.v tb.v -o main_bambu
./main_bambu | tee out.bambu.txt

checksum = 00000000