[cfe-dev] Big slowdown introduced in r92348

Douglas Gregor dgregor at apple.com
Tue Jan 12 10:27:46 CST 2010


On Jan 12, 2010, at 2:41 AM, Abramo Bagnara wrote:

> Il 12/01/2010 00:40, Douglas Gregor ha scritto:
>> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20100111/026231.html
>> 
>> 
>> On Jan 11, 2010, at 9:16 AM, Abramo Bagnara wrote:
>> 
>>> 
>>> Using as usual the big gcc.c source from
>>> 
>>> http://people.csail.mit.edu/smcc/projects/single-file-programs/
>>> 
>>> $ time ~/llvm_opt/Release/bin/clang -w -fsyntax-only gcc.c
>>> 
>>> real    0m3.792s
>>> user    0m3.472s
>>> sys    0m0.319s
>>> $ time ~/llvm_opt/Release/bin/clang -w -fsyntax-only gcc.c
>>> 
>>> real    0m13.384s
>>> user    0m13.046s
>>> sys    0m0.335s
>>> 
>>> Using bisection I've found the culprit in commit r92348.
>>> 
>>> Why a modify to Sema::LookupTemplateName could impact a non C++ program
>>> is beyond my comprehension, but perhaps the name of function is
>>> misleading I don't know...
>> 
>> This should be fixed in r93207, here:
>> 
>>    http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20100111/026231.html
>> 
>> 
>> I can't check your particular example on my system (since I don't have
>> all of the headers that gcc.c relies on), but the change improved
>> performance on Cocoa.h. Actually, since this change eliminates a bunch
>> of extra name lookup, r93207 may even be faster than r92347 was.
> 
> I've just tested it and now it's fast as before for gcc.c (not faster).

Okay, good.

> However I leave to you the evaluation about whether the slowdown
> introduced by r92348 is appropriate or not for C++ programs.

I'll look into that, too. Thanks.

	- Doug




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