[PATCH] Quick look-up for block in loop

[Hal Finkel]

Wan,

Do you think that it would be worthwhile to cache the DenseSet once constructed?

Also, in LCSSA, we currently keep a cache of the sorted loop blocks array, solely for the purpose of this function:

    /// inLoop - returns true if the given block is within the current loop
    bool inLoop(BasicBlock *B) const {
      return std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), B);
    }

With this new, more-efficient, functionality in LoopInfo, especially if we cache the resulting set, I think that it would make sense to remove this inLoop implementation from LCSSA and let it call the regular contains(BB) function.

Finally, when you post patches to llvm-reviews, please generate them with -U999999 so that we can see the full context in the web interface.

Thanks,
Hal

----- Original Message -----
> Hi atrick,
> 
> In LoopInfo.cpp and LoopInfoImpl.h, it is frequently to judge a
> specified block is in a loop or not, eg. getExitBlocks();
> 
> Currently the implementation is like this:
> a. Copy all blocks into a vector and sort it, then use binary search
> to look up it.
> b. Construct SmallPtrSet to implement quick search, when the set is
> small, it is same as the linear search in vector.
> 
> These two ways are proven very inefficient, it causes 2~4%
> performance penalty of llc for the cases with many loops; such as
> 458.sjeng, 429.mcf, 456.hmmer in CPUSpec2006.
> 
> This patch implement quick_contains() to look up a block in loop:
> 1. when the block size is small, look up the block vector directly to
> avoid construction of any other data container.
> 2. otherwise construct DenseSet to implement quick look-up.
> 
> This patch could introduce 2~3% compilation time improvement in llc
> for the benchmark with many loops.
> 
> http://llvm-reviews.chandlerc.com/D2014
> 
> Files:
>   include/llvm/Analysis/LoopInfo.h
>   include/llvm/Analysis/LoopInfoImpl.h
>   lib/Analysis/LoopInfo.cpp
> 
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> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory