[cfe-dev] Clang Slow to Optimize Dead Store Elimination

[Philip Reames]

On 01/13/2015 10:09 AM, Chris Jung wrote:
> I have an Objective-C file that’s about 6000 lines long, which is 
> nearly all a NSArray of 550 items, each of which is a NSDictionary 
> with NSString/NSString and NSString/NSNumber key value pairs in 
> literal syntax. This code takes about 0.4s to compile if optimizations 
> are turned off. It takes about 8 minutes to compile if -O1 is turned 
> on. It takes about 13 minutes to compile if "-fobjc-arc" option is 
> given with -O1. The time-report indicates that Dead Store Elimination 
> optimization is taking the majority of the time. Is it worth logging a 
> bug or is that working as intended? 
Please file a bug (with a reproducer).  DSE really shouldn't be anywhere 
near that slow.

p.s. If you happen to have a performance profile handy, I'd be curious 
to know where the slowdown was.

Philip

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