Write an IR visitor

Rakefile

@@ -49,20 +49,26 @@ task test: BINARY do
       .new(test)
       .sub_ext('.txt')
       .sub(/^build\/[[:alpha:]]+\//, 'tests/expectations/')
-      .read
-      .to_i
+      .to_path
 
     puts "Running #{test}"
     if test.include? '/riscv/'
-      system('/opt/riscv/bin/spike',
-        '/opt/riscv/riscv32-unknown-elf/bin/pk', test,
-        { out: '/dev/null' })
+      spike = [
+        '/opt/riscv/bin/spike',
+        '/opt/riscv/riscv32-unknown-elf/bin/pk',
+        test
+      ]
+      diff = ['diff', '-Nur', '--color', expected, '-']
+      tail = ['tail', '-n', '1']
+
+      last_stdout, wait_threads = Open3.pipeline_r spike, tail, diff
     else
       raise 'Unsupported test platform'
     end
-    actual = $?.exitstatus
+    print last_stdout.read
+    last_stdout.close
 
-    fail "#{test}: Expected #{expected}, got #{actual}" unless expected == actual
+    fail unless wait_threads.last.value.exitstatus.zero?
   end
 end