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<title>Writing an LLVM Pass</title>
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LEVEL = ../../..
# Name of the library to build
-LIBRARYNAME = hello
+LIBRARYNAME = Hello
-# Build a dynamically loadable shared object
+# Build a dynamically linkable shared object
SHARED_LIBRARY = 1
+# Make the shared library become a loadable module so the tools can
+# dlopen/dlsym on the resulting library.
+LOADABLE_MODULE
+
# Include the makefile implementation stuff
include $(LEVEL)/Makefile.common
</pre>
<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
directory are to be compiled and linked together into a
-<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
-the <tt>opt</tt> or <tt>analyze</tt> tools. If your operating system uses a
-suffix other than .so (such as windows or Mac OS/X), the appropriate extension
-will be used.</p>
+<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
+the <tt>opt</tt> or <tt>analyze</tt> tools via their <tt>-load</tt> options.
+If your operating system uses a suffix other than .so (such as windows or
+Mac OS/X), the appropriate extension will be used.</p>
<p>Now that we have the build scripts set up, we just need to write the code for
the pass itself.</p>
<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
command in the local directory and you should get a new
-"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
+"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
contained in an anonymous namespace: this reflects the fact that passes are self
contained units that do not need external interfaces (although they can have
them) to be useful.</p>
work):</p>
<pre>
-$ opt -load ../../../lib/Debug/libhello.so -hello < hello.bc > /dev/null
+$ opt -load ../../../Debug/lib/Hello.so -hello < hello.bc > /dev/null
Hello: __main
Hello: puts
Hello: main
<tt>opt</tt> with the <tt>--help</tt> option:</p>
<pre>
-$ opt -load ../../../lib/Debug/libhello.so --help
+$ opt -load ../../../Debug/lib/Hello.so --help
OVERVIEW: llvm .bc -> .bc modular optimizer
USAGE: opt [options] <input bytecode>
example:</p>
<pre>
-$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes < hello.bc > /dev/null
+$ opt -load ../../../Debug/lib/Hello.so -hello -time-passes < hello.bc > /dev/null
Hello: __main
Hello: puts
Hello: main
Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
<pre>
-$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
+$ opt -load ../../../Debug/lib/Hello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
Module Pass Manager
Function Pass Manager
Dominator Set Construction
World</a> pass in between the two passes:</p>
<pre>
-$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
Module Pass Manager
Function Pass Manager
Dominator Set Construction
<p>Now when we run our pass, we get this output:</p>
<pre>
-$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
Pass Arguments: -gcse -hello -licm
Module Pass Manager
Function Pass Manager