llvm dev - Jun 2010 - [LLVMdev] build errors while cross compiling llvm-gcc for ARM

> But I wanted to say is using these binutils I have built a llvm compiler
for
> our ARM target.
That's correct. Mostly because gcc is using pre-UAL ARM assembler syntax
and LLVM switched fully to UAL one. Also, UAL is needed for correct Thumb-2
support, etc. So, in short: gcc is generating some subset of ARM assembler
and thus gas is bug-free. LLVM generates somehow different subset and this
uncovered many bugs inside gas :)
> Now our libraries which are either compiled with native ARM or with this
> llvm compiler gives same performance numbers. However this only llvm
> compiler if compared with x86 compiler gives huge performance gain.
You mean that llvm-generated code is faster on x86, but not on ARM compared
to the vendor compiler / gcc, right?

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

exactly

On Mon, Jun 28, 2010 at 2:11 PM, Anton Korobeynikov <anton at
korobeynikov.info
> wrote:
> > But I wanted to say is using these binutils I have built a llvm
compiler
> for
> > our ARM target.
> That's correct. Mostly because gcc is using pre-UAL ARM assembler
syntax
> and LLVM switched fully to UAL one. Also, UAL is needed for correct Thumb-2
> support, etc. So, in short: gcc is generating some subset of ARM assembler
> and thus gas is bug-free. LLVM generates somehow different subset and this
> uncovered many bugs inside gas :)
>
> > Now our libraries which are either compiled with native ARM or with
this
> > llvm compiler gives same performance numbers. However this only llvm
> > compiler if compared with x86 compiler gives huge performance gain.
> You mean that llvm-generated code is faster on x86, but not on ARM compared
> to the vendor compiler / gcc, right?
>
> --
>  With best regards, Anton Korobeynikov
> Faculty of Mathematics and Mechanics, Saint Petersburg State University
>
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> exactly
Well, in general, there is no connection between the performance on
x86 and on ARM.
You can try to profile your code and find what causes the speedup on
x86 and figure out the slowdowns on ARM.

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University