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Re: [Xen-devel] [PATCH 2/2] tools: detect appropriate debug optimization level

On 3/30/16 11:00 AM, Ian Jackson wrote:
> Doug Goldstein writes ("Re: [PATCH 2/2] tools: detect appropriate debug 
> optimization level"):
>> On 3/8/16 9:38 AM, Wei Liu wrote:
>>> On Mon, Mar 07, 2016 at 08:23:40PM -0600, Doug Goldstein wrote:
>>>> The build should not use -O0 as that results in miscompilations. There
>>> This needs some (concrete) references. Is that a known issue in gcc? If
>>> so can you reference the bug number?
>> So its not really a bug in GCC but just the complete lack of
>> optimizations in play. inlines aren't inlined. dead code elimination
>> isn't run so things are much bigger. structures aren't padded the same way.
> My initial reaction is that I any actual problems are bugs either in
> the compiler or in Xen, which should be fixed.
> There should be nothing wrong with lack of inlining or dead code
> elimination.  If you can give an example of structure padding going
> wrong, please do.
> Ian.

Ok fine, I'm just confused why we're insisting on using -O0 over -Og?

From the gcc manual:

Optimize debugging experience. -Og enables optimizations that do not
interfere with debugging. It should be the optimization level of choice
for the standard edit-compile-debug cycle, offering a reasonable level
of optimization while maintaining fast compilation and a good debugging

Doug Goldstein

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