llvm dev - Mar 2016 - RelWithDebInfo vs Release optimization level?

Hi all,

These two cmake configuration are using different optimization levels (O2 vs
O3). What is the rational for that? I know that O1 is "supposingly"
more friendly for debugging, but I don't think we make such claim for O2 vs
O3, are we?

I'd expect RelWithDebInfo to be what the name says, i.e. Release +
debug-information.


-- 
Mehdi

I also assumed they were the same, and I have been using them
that way.  I agree they should match.
> On 2016-Mar-15, at 15:20, Mehdi Amini via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi all,
> 
> These two cmake configuration are using different optimization levels (O2
vs O3). What is the rational for that? I know that O1 is "supposingly"
more friendly for debugging, but I don't think we make such claim for O2 vs
O3, are we?
> 
> I'd expect RelWithDebInfo to be what the name says, i.e. Release +
debug-information.
> 
> 
> -- 
> Mehdi
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

The default values for the optimization level are provided by CMake. My stab in
the dark here is that the difference originates as a behavior matching Visual
Studio. Historically VS lowered optimization to -O2 if you built with debug info
because the -O3 builds were basically undebugable.

Changing this default in our CMake configurations might be tricky and error
prone because there isn't a good way to know that the variable isn't set
by the user. This is basically the perennial CMake cache invalidation problem.

-Chris
> On Mar 15, 2016, at 4:44 PM, Duncan P. N. Exon Smith via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 
> I also assumed they were the same, and I have been using them
> that way.  I agree they should match.
> 
>> On 2016-Mar-15, at 15:20, Mehdi Amini via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
>> 
>> Hi all,
>> 
>> These two cmake configuration are using different optimization levels
(O2 vs O3). What is the rational for that? I know that O1 is
"supposingly" more friendly for debugging, but I don't think we
make such claim for O2 vs O3, are we?
>> 
>> I'd expect RelWithDebInfo to be what the name says, i.e. Release +
debug-information.
>> 
>> 
>> -- 
>> Mehdi
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev