<tt>bugpoint</tt>
<h3>SYNOPSIS</h3>
-<tt>bugpoint [options] [input llvm ll/bc files] [LLVM passes] --args <program arguments>...</tt>
+<tt>bugpoint [options] [input LLVM ll/bc files] [LLVM passes] --args <program arguments>...</tt>
<img src="../Debugging.gif" width=444 height=314 align=right>
<h3>DESCRIPTION</h3>
-The <tt>bugpoint</tt> tool is a generally useful tool for narrowing down
-problems in LLVM tools and passes.<p>
-
-<tt>bugpoint</tt> reads the specified list of .bc or .ll files specified on the
-command-line and links them together. It then runs the specified LLVM passes on
-the resultant bytecode file. If any of the passes crash, or if they produce an
-LLVM module which is not verifiable, bugpoint enters "crash debugging mode".
-Otherwise, <tt>bugpoint</tt> tries to run the resultant program with a code
-generator. If the code generated program does not match the reference output,
-it enters "miscompilation debugging mode". If the <tt>-mode</tt> option is
-specified, <tt>bugpoint</tt> enters "code generator debugging mode".
-
-<h4>Crash debugging mode</h4>
-
-If a pass crashes, bugpoint will try to narrow down the list of passes and the
-code to a more manageable amount. Using a sophisticated binary-search algorithm,
-<tt>bugpoint</tt> pares down the list of passes to a minimum set.
-[unfinished]
-
-<h4>Miscompilation debugging mode</h4>
-
-TODO
-
-<h4>Code generator debugging mode</h4>
-
-TODO
-
+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 invalid native
+code generation. 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 a lot of 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. :-) <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,
+<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 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>
+
+Otherwise, <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 crashes, <tt>bugpoint</tt> will try as hard as it can to
+reduce the list of passes and the size of the test program. First,
+<tt>bugpoint</tt> figures out which combination of passes triggers the bug. This
+is useful when debugging a problem exposed by <tt>gccas</tt>, for example,
+because it runs over 25 optimizations.<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> or
+<tt><a href="analyze.html">analyze</a></tt>.<p>
+
+<a name="codegendebug">
+<h4>Code generator debugger</h4>
+
+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>
+
+If you are using the code generator debugger and get an error message that
+says "Non-instruction
+is using an external function!", try using the <tt>-run-llc</tt> option instead
+of the <tt>-run-jit</tt> option. This is due to an unimplemented feature in the
+code generator debugger.<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 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 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.
+
+</ol>
<h3>OPTIONS</h3>
<ul>
- <li><tt>-args <arguments></tt>
- <br>
- All arguments specified after <tt>-args</tt> are passed into the
- executed program when the program must be executed.
+ <li><tt>-additional-so <library.so></tt><br>
+ Load <tt><library.so></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>-disable-{adce,dce,final-cleanup,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>
- <li><tt>-disable-(adce,dce,final-cleanup,simplifycfg)</tt>
- <br>
- <tt>bugpoint</tt> uses several passes internally for cleanup routines to
- reduce the size of the program. If you're trying to find a bug in out
- of these passes, <tt>bugpoint</tt> may crash. These options tell
- <tt>bugpoint</tt> not use the specified passes.
- <p>
-
- <li> <tt>-help</tt>
- <br>
- Print a summary of command line options.
- <p>
-
- <li> <tt>-input <filename></tt>
- <br>
- Specify the contents of <stdin> when the program must be executed.
- <p>
-
- <li> <tt>-load <plugin.so></tt>
- <br>
- Load the dynamic object plugin.so. This object should register new
+ <a name="opt_load"><li> <tt>-load <plugin.so></tt><br>
+ Load the dynamic object <tt><plugin.so></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>opt -load <plugin.so> -help</tt>
- <p>
-
- <li> <tt>-mode=(compile|codegen)</tt>
- <br>
- Specify whether <tt>bugpoint</tt> should operate in compilation
- debugging mode (detecting miscompilations and optimizer crashes), or in
- code generator debugging mode.
- <p>
-
- <li> <tt>-output <filename></tt>
- <br>
- Specify a reference output for the <stdout> file stream.
- <p>
-
- <li> <tt>-run-(lli|jit|llc|cbe)</tt>
- <br>
- Specify which code generator <tt>bugpoint</tt> should use to run the
- program with.
+ <tt>bugpoint -load <plugin.so> -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>
+
+ <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>
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="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>.
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projects / oota-llvm.git / blobdiff