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

>> There are probably other differing defaults besides frame pointers. 
Stack
>> protectors, perhaps.
>
> Yes, that's another good example,
Ok-- I assume I should just add '-fno-stack-protector' to the llvm-gcc
and
clang command lines?  I had totally missed that something like this was 
turned on by default.

I'll re-run everything with this change, with frame pointers omitted, and 
dropping testcases that contain uses of uninititalized locals and post 
here again when that's done.

Thanks for the feedback,

John

On Dec 14, 2009, at 12:23 PM, John Regehr wrote:
>>> There are probably other differing defaults besides frame  
>>> pointers.  Stack
>>> protectors, perhaps.
>>
>> Yes, that's another good example,
>
> Ok-- I assume I should just add '-fno-stack-protector' to the llvm-
> gcc and
> clang command lines?  I had totally missed that something like this  
> was
> turned on by default.
>
> I'll re-run everything with this change, with frame pointers  
> omitted, and
> dropping testcases that contain uses of uninititalized locals and post
> here again when that's done.
Sounds great, thanks John!

-Chris

On Dec 14, 2009, at 12:23 PMPST, John Regehr wrote:
>>> There are probably other differing defaults besides frame  
>>> pointers.  Stack
>>> protectors, perhaps.
>>
>> Yes, that's another good example,
>
> Ok-- I assume I should just add '-fno-stack-protector' to the llvm-
> gcc and
> clang command lines?  I had totally missed that something like this  
> was
> turned on by default.
Yes.
> I'll re-run everything with this change, with frame pointers  
> omitted, and
> dropping testcases that contain uses of uninititalized locals and post
> here again when that's done.
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?

I think some useful information is going to come out of this, but  
there's some cruft to clear out first.

> 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

> 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?
I saw in some tests the difference of the size was caused by different
defaults for FP codegen - x87 math or sse2.

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