[PATCH] [Review Request] Numbering SDNode to discard SmallPtrSet in selection DAG

[Wan, Xiaofei]

Thanks for your review.

1. SmallBitVector can meet what FlagVector can after some minor changes, but for the convenience of review, I don't want to change it since it is a common container which is used by most people, I will change to use SmallBitVector instead of FlagVector.

2. SmallBitVector is usually O(1), but the overhead to construct this set is hot, the insert_impl is very hot.



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-----Original Message-----
From: Benjamin Kramer [mailto:benny.kra at gmail.com]
Sent: Friday, July 12, 2013 6:04 PM
To: resistor at mac.com; Wan, Xiaofei
Cc: llvm-commits at cs.uiuc.edu; benny.kra at gmail.com
Subject: Re: [PATCH] [Review Request] Numbering SDNode to discard SmallPtrSet in selection DAG





  Some high level comments:



  - SmallPtrSet is usually O(1) but falls back to linear search when it's small. SmallPtrSet<64> is way too large, have you benchmarked with the small capacity lowered to 8 or 16? This of course adds malloc overhead in more cases but we might get away with it.



  If the above fails:

  - I really don't see the point of FlagVector. Why not just use a SmallVector (or SmallBitVector as we're only storing bools) and resize appropriately when it's used. In any case, the class does not belong in SmallVector.h.



http://llvm-reviews.chandlerc.com/D1129
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