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Always say "the test program", part 2.

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Refer to the various "modules" of bugpoint as "debuggers", not
 "debugging modes" or "modules". I think this is more evocative of
 how they typically act, and it's shorter.
Add a note about how a linker bug can crash bugpoint early.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@9257 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Brian Gaeke 2003-10-19 17:30:36 +00:00
parent 129e7a88b0
commit 6ff3310c49
1 changed files with 36 additions and 30 deletions
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@ -36,15 +36,15 @@ 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="automaticmodeselection">
<h4>Automatic Mode Selection</h4>
<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 a malformed LLVM module,
<tt>bugpoint</tt> enters <a href="#crashdebug">crash debugging mode</a>.<p>
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
@ -53,18 +53,18 @@ is assumed to generate good code) to generate a reference output. Once
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 enters
<a href="#codegendebug">code generator debugging mode</a>.<p>
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
<a href="#miscompilationdebug">miscompilation debugging mode</a>. Otherwise,
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 debugging mode</h4>
<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,
@ -72,8 +72,9 @@ reduce the list of passes and the size of the test program. First,
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 module, to reduce the
size of the test program. Usually it is able to reduce a test program
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
@ -85,36 +86,37 @@ 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 debugging mode</h4>
<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 LLVM program and partitions it into two pieces: one piece
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 (the "test" [to be compiled with the code generator] and
"safe" [to be compiled with the C backend] modules), and instructions for
reproducing the problem. This module assume the C backend produces good
code.<p>
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 this mode and get an error message that says "Non-instruction
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 debugging mode.<p>
code generator debugger.<p>
<a name="miscompilationdebug">
<h4>Miscompilation debugging mode</h4>
<h4>Miscompilation debugger</h4>
The miscompilation debugging mode works similarly to the code generator
debugging mode. It works by splitting the program into two pieces, running the
optimizations specified on one piece, relinking the program, then executing it.
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 program which is
being miscompiled. This module assumes that the selected code generator is
working properly.<p>
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>
@ -123,14 +125,14 @@ working properly.<p>
non-obvious ways. Here are some hints and tips:<p>
<ol>
<li>In code generator and miscompilation debugging modes, <tt>bugpoint</tt> only
<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 code generator and miscompilation debugging modes, debugging will go
<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.
@ -147,9 +149,13 @@ non-obvious ways. Here are some hints and tips:<p>
<br>to get a copy of <tt>bugpoint</tt>'s output in the file
<tt>bugpoint.log</tt>, as well as on your terminal.<p>
<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>