[LLVMdev] Some understanding of LLVM vs gCC vs Intel C++ Compilers

David Greene dag at cray.com
Tue Jun 16 15:05:48 PDT 2009

On Tuesday 16 June 2009 09:49, Dan Gohman wrote:
> Trying to capture a notion of overall compiler optimization
> in a representative set of benchmarks is a hard problem.
> If you're interested in performance, it's best to measure it
> on the applications you're interested in.
> You should be suspicious of any one-dimensional analysis
> of compiler optimization, especially if it's presented by
> someone with an interest in a particular compiler.

That's exactly right.

I have seen codes where even minor tweaks to a register allocation spilling 
heuristic can have a 10-20% performance impact on X86.  Compiler 
transformations are often very sensitive to particular pieaces of code.

It's impossible to declare one compiler "better" than another because it's 
likely the design goals of the compilers are quite different.

The great advantage of LLVM/Clang, in my mind, is its clean design and
relatively shallow learning curve.  It's not only a smart business decision
to use the code because of its utilitarian value, it's smart from an
employee training perspective as well.

All IMHO, nothing I say here is an official Cray position, blah, blah, 
blah.  :)


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