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On Sun, 2003-11-16 at 10:44, Chris Lattner wrote:
<BLOCKQUOTE TYPE=CITE>
<PRE><FONT COLOR="#301fe4"><I>> In other words, I'd like to take a set of bytecode files, optimize them
> together even though they don't form a complete program, and then write
> out the new (optimized) bytecode files. It would be preferable to write
> them out to a single archive rather than to individual bytecode files
> again. Can this be done in LLVM today? If not, what would it take to
> implement?
I'm not sure exactly what you want, but we do already have a form of this.
If you use the low-level llvm-link program (or gccld --link-as-library),
it will take all of the .bc files specified, link them together into a
_single_ bytecode file, and write that out (gccld performs IPO on the
result).</I></FONT></PRE>
</BLOCKQUOTE>
Okay.
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<PRE><FONT COLOR="#301fe4"><I>
Is this what you mean? Is there any reason to keep the .bc files distinct
like a ".a" file, or is it ok for your purposes to link them together into
a single unit, like a ".so" file?</I></FONT></PRE>
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Well, the answer depends on whether the individual modules are separately loadable or not. Suppose the<BR>
resulting bytecode file gets JIT loaded into a running program. Is it all or nothing? What if the calling program<BR>
new it needed a specific module from the larger optimized "package"? Can the original modules, now <BR>
combined into the one .bc file, get loaded individually? <BR>
<BR>
For example, using Java, suppose I wanted to use java.util.zip.CRC32 to compute a checksum in a program.<BR>
That class (module) is delivered to me as a java.util.zip "package". That is, it is the result of running llvm-link<BR>
to produce a single bytecode file that includes all the classes with java.util.zip prefix. But (for some mysterious <BR>
reason) the java.util.zip/CRC32 class was not compiled/linked/optimized into my program; its just referenced <BR>
from it. At runtime, the JIT needs to locate this module and compile/link it into my program. Now, if the <BR>
CRC32 class (module) is part of a java.util.zip package (i.e. the output of llvm-link), what happens?<BR>
Is the entire package loaded providing more than my program needs? Is the runtime linker smart enough to <BR>
locate the CRC32 module in the optimized package output? Is it smart enough to load only the one module <BR>
needed? Does the notion of module inside a module even exist?<BR>
<BR>
P.S. Bug 114 (-Wold-style-cast) has a patch ready.<BR>
<BR>
Reid
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