[LLVMdev] a question about LLCO

[Reid Spencer]

Hi Terry,

I'm not part of that project but I'll take a stab at answering your
question. Vikram Adve is probably the person to answer.

The point of Lifelong Code Optimization is to continuously optimize the
code during its lifetime, even while it is running. By profiling the
code, it is possible to discover the program's hot spots and intensely
optimize those portions of the program. Since we're talking about pretty
intense optimization here, we're generally not talking about interpreted
or dynamically linked software. The overhead of dynamically linking a
library can be very large and it thwarts some of the goals of LLCO. When
the *whole* program is represented in LLVM, it is possible to apply
optimizations that you couldn't do otherwise. If portions of the program
are dynamically loaded then these optimizations are not available. For
example, if you have the entire program to ponder, it would allow you to
remove dead globals variables or functions. These things might become
dead via inlining or other code rearrangement. 

Reid.

On Sun, 2005-05-22 at 13:49 +0800, hua lei wrote:
> Hi everybody,
>   
>   Recently, I found the Lifelong Code Optimization project on the
> website. And I have a question here, would you please explain it for
> me?
> 
>   In the home page of the project, it is said that the Goal of the
> project is to enable mordern programs to be optimized at link time
> with all static binary code. Here I wonder, why the library code must
> be static, i.e. why a dynamically linked program is not considered?
> Since most of our daily used programs are dynamically linked.
>  
>   Thanks a lot.
> 
> Best wishes
> terry
> 
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