[cfe-commits] [patch] Qualifiers refactor

[Douglas Gregor]

On Sep 25, 2009, at 6:50 PM, Chris Lattner wrote:

> On Sep 24, 2009, at 8:58 AM, Douglas Gregor wrote:
> On Sep 23, 2009, at 2:04 AM, John McCall wrote:
>>> The attached patch refactors how qualifiers are represented in  
>>> clang.
>>>
>>> Currently, QualType uses the bottom three bits of a type pointer to
>>> represent the const, volatile, and restrict qualifiers.  Extended
>>> qualifiers are represented using an ExtQualType object, which is an
>>> ordinary node in the type hierarchy --- except that it isn't.  Most
>>> common operations on types have to explicitly check for these
>>> special qualifier nodes and handle them differently.
>>
>> ... except that most common operations end up forgetting that
>> ExtQualType exists. One of the big benefits of this change is that  
>> all
>> of the qualifiers are kept together, so it's easier to reason about
>> them as a whole. Plus, ExtQualType didn't fit well into the type
>> system; this does.
>
> I also really like this change.  However, 4% is a really big  
> slowdown.  Where is the time going?

It looks like it's spread out; nothing specific floated upward in the  
Shark trace. My (bleak) hypothesis is that we''re getting death-by-a- 
thousand-cuts from QualType::getTypePtr(), which is ubiquitous and now  
has a branch.

	- Doug