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Re: [PATCH] PR63300 'const volatile' sometimes stripped in debug info.


On 09/24/2014 01:05 PM, Mark Wielaard wrote:
On Wed, 2014-09-24 at 10:47 -0400, Jason Merrill wrote:
On 09/23/2014 06:53 PM, Mark Wielaard wrote:
And for the default case (gcc doesn't
create type sections by default) the optimization is useful.

I'm skeptical.  These DIEs are very small, and I wouldn't expect a hole
in the qualifier space like this to come up that often.

But if you don't take the optimization (re-use an existing sub-qualified
type when you have a type with multiple qualifiers) then you might have
to pessimize (o, there is already such a sub-qualified type, but I have
to first create a different sub-qualified type because the order will
come out "wrong"). So you might end up with extra type DIEs then.

Yes, but I think the net effect of this is very small.

Anyway. I don't think this should hold up this specific bug fix. The
issue with type units vs qualified type DIEs has been there in all
previous versions of GCC (and only when using non-default flags). It
really comes from DWARF not specifying anything about the ordering of
type modifier tags.

But GCC has been consistent about the ordering, and I would prefer not to change that; I would expect it to hurt dwz compression as well as type units.

Jason


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