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+<html>
+<title>LLVM: bugpoint tool</title>
+
+<body bgcolor=white>
+
+<center><h1>LLVM: <tt>bugpoint</tt> tool</h1></center>
+<HR>
+
+<h3>NAME</h3>
+<tt>bugpoint</tt>
+
+<h3>SYNOPSIS</h3>
+<tt>bugpoint [options] [input LLVM ll/bc files] [LLVM passes] --args <program arguments>...</tt>
+
+<img src="../img/Debugging.gif" width=444 height=314 align=right>
+<h3>DESCRIPTION</h3>
+
+The <tt>bugpoint</tt> tool narrows down the source of
+problems in LLVM tools and passes. It can be used to debug three types of
+failures: optimizer crashes, miscompilations by optimizers, or bad native
+code generation (including problems in the static and JIT compilers). It aims
+to reduce large test cases to small, useful ones. For example,
+if <tt><a href="gccas.html">gccas</a></tt> crashes while optimizing a file, it
+will identify the optimization (or combination of optimizations) that causes the
+crash, and reduce the file down to a small example which triggers the crash.<p>
+
+<a name="designphilosophy">
+<h4>Design Philosophy</h4>
+
+<tt>bugpoint</tt> is designed to be a useful tool without requiring any
+hooks into the LLVM infrastructure at all. It works with any and all LLVM
+passes and code generators, and does not need to "know" how they work. Because
+of this, it may appear to do stupid things or miss obvious
+simplifications. <tt>bugpoint</tt> is also designed to trade off programmer
+time for computer time in the compiler-debugging process; consequently, it may
+take a long period of (unattended) time to reduce a test case, but we feel it
+is still worth it. Note that <tt>bugpoint</tt> is generally very quick unless
+debugging a miscompilation where each test of the program (which requires
+executing it) takes a long time.<p>
+
+<a name="automaticdebuggerselection">
+<h4>Automatic Debugger Selection</h4>
+
+<tt>bugpoint</tt> reads each <tt>.bc</tt> or <tt>.ll</tt> file
+specified on the command line and links them together into a single module,
+called the test program. If any LLVM passes are
+specified on the command line, it runs these passes on the test program. If
+any of the passes crash, or if they produce malformed output (which causes the
+verifier to abort),
+<tt>bugpoint</tt> starts the <a href="#crashdebug">crash debugger</a>.<p>
+
+Otherwise, if the <a href="#opt_output"><tt>-output</tt></a> option was not
+specified, <tt>bugpoint</tt> runs the test program with the C backend (which is
+assumed to generate good code) to generate a reference output. Once
+<tt>bugpoint</tt> has a reference output for the test program, it tries
+executing it with the <a href="#opt_run-">selected</a> code generator. If the
+selected code generator crashes, <tt>bugpoint</tt> starts the <a
+href="#crashdebug">crash debugger</a> on the code generator. Otherwise, if the
+resulting output differs from the reference output, it assumes the difference
+resulted from a code generator failure, and starts the <a
+href="#codegendebug">code generator debugger</a>.<p>
+
+Finally, if the output of the selected code generator matches the reference
+output, <tt>bugpoint</tt> runs the test program after all of the LLVM passes
+have been applied to it. If its output differs from the reference output, it
+assumes the difference resulted from a failure in one of the LLVM passes, and
+enters the <a href="#miscompilationdebug">miscompilation
+debugger</a>. Otherwise, there is no problem <tt>bugpoint</tt> can debug.<p>
+
+<a name="crashdebug">
+<h4>Crash debugger</h4>
+
+If an optimizer or code generator crashes, <tt>bugpoint</tt> will try as hard as
+it can to reduce the list of passes (for optimizer crashes) and the size of the
+test program. First, <tt>bugpoint</tt> figures out which combination of
+optimizer passes triggers the bug. This is useful when debugging a problem
+exposed by <tt>gccas</tt>, for example, because it runs over 38 passes.<p>
+
+Next, <tt>bugpoint</tt> tries removing functions from the test program, to
+reduce its size. Usually it is able to reduce a test program to a single
+function, when debugging intraprocedural optimizations. Once the number of
+functions has been reduced, it attempts to delete various edges in the control
+flow graph, to reduce the size of the function as much as possible. Finally,
+<tt>bugpoint</tt> deletes any individual LLVM instructions whose absence does
+not eliminate the failure. At the end, <tt>bugpoint</tt> should tell you what
+passes crash, give you a bytecode file, and give you instructions on how to
+reproduce the failure with <tt><a href="opt.html">opt</a></tt>, <tt><a
+href="analyze.html">analyze</a></tt>, or <tt><a href="llc.html">llc</a></tt>.<p>
+
+<a name="codegendebug">
+<h4>Code generator debugger</h4>
+
+<p>The code generator debugger attempts to narrow down the amount of code that
+is being miscompiled by the <a href="#opt_run-">selected</a> code generator. To
+do this, it takes the test program and partitions it into two pieces: one piece
+which it compiles with the C backend (into a shared object), and one piece which
+it runs with either the JIT or the static LLC compiler. It uses several
+techniques to reduce the amount of code pushed through the LLVM code generator,
+to reduce the potential scope of the problem. After it is finished, it emits
+two bytecode files (called "test" [to be compiled with the code generator] and
+"safe" [to be compiled with the C backend], respectively), and instructions for
+reproducing the problem. The code generator debugger assumes that the C backend
+produces good code.</p>
+
+<a name="miscompilationdebug">
+<h4>Miscompilation debugger</h4>
+
+The miscompilation debugger works similarly to the code generator
+debugger. It works by splitting the test program into two pieces, running the
+optimizations specified on one piece, linking the two pieces back together,
+and then executing the result.
+It attempts to narrow down the list of passes to the one (or few) which are
+causing the miscompilation, then reduce the portion of the test program which is
+being miscompiled. The miscompilation debugger assumes that the selected
+code generator is working properly.<p>
+
+<a name="bugpoint notes">
+<h4>Advice for using <tt>bugpoint</tt></h4>
+
+<tt>bugpoint</tt> can be a remarkably useful tool, but it sometimes works in
+non-obvious ways. Here are some hints and tips:<p>
+
+<ol>
+<li>In the code generator and miscompilation debuggers, <tt>bugpoint</tt> only
+ works with programs that have deterministic output. Thus, if the program
+ outputs <tt>argv[0]</tt>, the date, time, or any other "random" data, <tt>bugpoint</tt> may
+ misinterpret differences in these data, when output, as the result of a
+ miscompilation. Programs should be temporarily modified to disable
+ outputs that are likely to vary from run to run.
+
+<li>In the code generator and miscompilation debuggers, debugging will go
+ faster if you manually modify the program or its inputs to reduce the
+ runtime, but still exhibit the problem.
+
+<li><tt>bugpoint</tt> is extremely useful when working on a new optimization:
+ it helps track down regressions quickly. To avoid having to relink
+ <tt>bugpoint</tt> every time you change your optimization however, have
+ <tt>bugpoint</tt> dynamically load your optimization with the <a
+ href="#opt_load"><tt>-load</tt></a> option.
+
+<li><tt>bugpoint</tt> can generate a lot of output and run for a long period of
+ time. It is often useful to capture the output of the program to file. For
+ example, in the C shell, you can type:<br>
+ <tt>bugpoint ..... |& tee bugpoint.log</tt>
+ <br>to get a copy of <tt>bugpoint</tt>'s output in the file
+ <tt>bugpoint.log</tt>, as well as on your terminal.
+
+<li><tt>bugpoint</tt> cannot debug problems with the LLVM linker. If
+ <tt>bugpoint</tt> crashes before you see its "All input ok" message,
+ you might try <tt>llvm-link -v</tt> on the same set of input files. If
+ that also crashes, you may be experiencing a linker bug.
+
+<li>If your program is <b>supposed</b> to crash, <tt>bugpoint</tt> will be
+ confused. One way to deal with this is to cause bugpoint to ignore the exit
+ code from your program, by giving it the <tt>-check-exit-code=false</tt>
+ option.
+
+</ol>
+
+<h3>OPTIONS</h3>
+
+<ul>
+ <li><tt>-additional-so <library></tt><br>
+ Load <tt><library></tt> into the test program whenever it is run.
+ This is useful if you are debugging programs which depend on non-LLVM
+ libraries (such as the X or curses libraries) to run.<p>
+
+ <li><tt>-args <program args></tt><br>
+ Pass all arguments specified after <tt>-args</tt> to the
+ test program whenever it runs. Note that if any of
+ the <tt><program args></tt> start with a '-', you should use:
+ <p>
+ <tt>bugpoint <bugpoint args> -args -- <program args></tt>
+ <p>
+ The "<tt>--</tt>" right after the <tt>-args</tt> option tells
+ <tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
+ part of the <tt>-args</tt> option, not as options to <tt>bugpoint</tt>
+ itself.<p>
+
+ <li><tt>-tool-args <tool args></tt><br>
+ Pass all arguments specified after <tt>-tool-args</tt> to the
+ LLVM tool under test (llc, lli, etc.) whenever it runs.
+ You should use this option in the following way:
+ <p>
+ <tt>bugpoint <bugpoint args> -tool-args -- <tool args></tt>
+ <p>
+ The "<tt>--</tt>" right after the <tt>-tool-args</tt> option tells
+ <tt>bugpoint</tt> to consider any options starting with <tt>-</tt> to be
+ part of the <tt>-tool-args</tt> option, not as options to
+ <tt>bugpoint</tt> itself. (See <tt>-args</tt>, above.)<p>
+
+ <li><tt>-check-exit-code={true,false}</tt><br>
+ Assume a non-zero exit code or core dump from the test program is
+ a failure. Defaults to true.<p>
+
+ <li><tt>-disable-{dce,simplifycfg}</tt><br>
+ Do not run the specified passes to clean up and reduce the size of the
+ test program. By default, <tt>bugpoint</tt> uses these passes internally
+ when attempting to reduce test programs. If you're trying to find
+ a bug in one of these passes, <tt>bugpoint</tt> may crash.<p>
+
+ <li> <tt>-help</tt><br>
+ Print a summary of command line options.<p>
+
+ <a name="opt_input"><li><tt>-input <filename></tt><br>
+ Open <tt><filename></tt> and redirect the standard input of the
+ test program, whenever it runs, to come from that file.
+ <p>
+
+ <a name="opt_load"><li> <tt>-load <plugin></tt><br>
+ Load the dynamic object <tt><plugin></tt> into <tt>bugpoint</tt>
+ itself. This object should register new
+ optimization passes. Once loaded, the object will add new command line
+ options to enable various optimizations. To see the new complete list
+ of optimizations, use the -help and -load options together:
+ <p>
+ <tt>bugpoint -load <plugin> -help</tt>
+ <p>
+
+ <a name="opt_output"><li><tt>-output <filename></tt><br>
+ Whenever the test program produces output on its standard output
+ stream, it should match the contents of <tt><filename></tt>
+ (the "reference output"). If you do not use this option,
+ <tt>bugpoint</tt> will attempt to generate a reference output by
+ compiling the program with the C backend and running it.<p>
+
+ <li><tt>-profile-info-file <filename></tt><br>
+ Profile file loaded by -profile-loader.<p>
+
+ <a name="opt_run-"><li><tt>-run-{int,jit,llc,cbe}</tt><br>
+ Whenever the test program is compiled, <tt>bugpoint</tt> should generate
+ code for it using the specified code generator. These options allow
+ you to choose the interpreter, the JIT compiler, the static native
+ code compiler, or the C backend, respectively.<p>
+</ul>
+
+<h3>EXIT STATUS</h3>
+
+If <tt>bugpoint</tt> succeeds in finding a problem, it will exit with 0.
+Otherwise, if an error occurs, it will exit with a non-zero value.
+
+<h3>SEE ALSO</h3>
+<a href="opt.html"><tt>opt</tt></a>,
+<a href="analyze.html"><tt>analyze</tt></a>
+
+<HR>
+Maintained by the <a href="http://llvm.cs.uiuc.edu">LLVM Team</a>.
+</body>
+</html>
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