llvm dev - Dec 2009 - [LLVMdev] detailed comparison of generated code size for LLVM and other compilers

> You'll probably need to  some digging to make sure the defaults are
exactly
> comparable.  Are SSE and/or MMX used?  This affects floating point codegen 
> quite a bit.  Are the target CPUs the same?
Good point.  Would "generic i686" be a reasonable choice?  Does that
even
mean anything these days?

Anyway-- I'd appreciate some guidance on what you folks would find most 
interesting and useful.  Then I can do some homework and figure out how to 
get the rest of the compilers to assume an equivalent ISA.

Thanks,

John

On Dec 14, 2009, at 1:49 PM, John Regehr wrote:
>> You'll probably need to  some digging to make sure the defaults are
>> exactly
>> comparable.  Are SSE and/or MMX used?  This affects floating point  
>> codegen
>> quite a bit.  Are the target CPUs the same?
>
> Good point.  Would "generic i686" be a reasonable choice?  Does
that
> even
> mean anything these days?
>
> Anyway-- I'd appreciate some guidance on what you folks would find  
> most
> interesting and useful.  Then I can do some homework and figure out  
> how to
> get the rest of the compilers to assume an equivalent ISA.
I'd recommend targeting (with both -march and -mtune) a simple and  
commonly available CPU type like "core2" or "pentium4".  ICC
should
have both of these and gcc/llvm definitely do.

-Chris

2009/12/14 Chris Lattner <clattner at apple.com>:
> I'd recommend targeting (with both -march and -mtune) a simple and
> commonly available CPU type like "core2" or "pentium4".
 ICC should
> have both of these and gcc/llvm definitely do.
While I would say that, to be fair, the comparison should be made with
the same options (-O3 only or something of the sort), ICC is specific
for Intel and GCC is highly tuned to, which is not the case of LLVM.
Still, if the target is specified, I'd assume we should enable all
tested and proven (AFAP) optimizations to that particular platform by
default.

So, my question is: are those optimizations turned off by default
because they're experimental?

--renato

http://systemcall.org/

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