[LLVMdev] Packages

[Reid Spencer]

On Sun, 2003-11-16 at 10:44, Chris Lattner wrote:

> > 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).

Okay.

> 
> 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?

Well, the answer depends on whether the individual modules are
separately loadable or not. Suppose the
resulting bytecode file gets JIT loaded into a running program. Is it
all or nothing? What if the calling program
new it needed a specific module from the larger optimized "package"? Can
the original modules, now 
combined into the one .bc file, get loaded individually? 

For example, using Java, suppose I wanted to use java.util.zip.CRC32 to
compute a checksum in a program.
That class (module) is delivered to me as a java.util.zip "package".
That is, it is the result of running llvm-link
to produce a single bytecode file that includes all the classes with
java.util.zip prefix. But (for some mysterious 
reason) the java.util.zip/CRC32 class was not compiled/linked/optimized
into my program; its just referenced 
from it.  At runtime, the JIT needs to locate this module and
compile/link it into my program. Now, if the 
CRC32 class (module) is part of a java.util.zip package (i.e. the output
of llvm-link), what happens?
Is the entire package loaded providing more than my program needs? Is
the runtime linker smart enough to 
locate the CRC32 module in the optimized package output? Is it smart
enough to load only the one module 
needed? Does the notion of module inside a module even exist?

P.S. Bug 114 (-Wold-style-cast) has a patch ready.

Reid
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