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...M, Vedant Kumar via llvm-dev <llvm-dev at lists.llvm.org> wrote: > >> On Apr 24, 2017, at 5:37 PM, Scott Smith via llvm-dev <llvm-dev at lists.llvm.org> wrote: >> >> I've been working on improving the startup performance of lldb, and ran into an issue with llvm::HashString. It works a character at a time, which creates a long dependency chain in the processor. On the other hand, the function is very short, which probably works well for short identifiers. >> >> I don't know how the mix of identifier length seen by lldb compares with that seen by l...

I've been working on improving the startup performance of lldb, and ran into an issue with llvm::HashString. It works a character at a time, which creates a long dependency chain in the processor. On the other hand, the function is very short, which probably works well for short identifiers. I don't know how the mix of identifier length seen by lldb compares with that seen by llvm/clang; I imag...

...for Clang's > identifier maps (via StringMap) and so I'd like to see some measurements > that ensure that these performance improvements translate over to Clang (or > at least don't regress). > > If Clang doesn't regress and xxHash is measurably better for other > HashString workloads, then I don't see a reason not to switch to it. > > -- Sean Silva > > On Mon, Apr 24, 2017 at 5:37 PM, Scott Smith via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> I've been working on improving the startup performance of lldb, and ran >...

...gRef StrVal) { addImpl(StrVal.data(), StrVal.size()); } I'm contradicting my stance above about not caring about the implementation :), but is MurmurHash a good hash for string data? The Bernstein hash function works really well and is much cheaper to compute than Murmur. It is used by HashString (and thus by StringMap). // Add a possibly unaligned sequence of bytes. void addImpl(const char *I, size_t Length) { This should probably be moved out of line to avoid code bloat. Overall, the design of the class is making sense to me! Thanks for tackling this! -Chris -------------- n...

...rVal.data(), StrVal.size()); > } > > I'm contradicting my stance above about not caring about the > implementation :), but is MurmurHash a good hash for string data? > The Bernstein hash function works really well and is much cheaper to > compute than Murmur. It is used by HashString (and thus by StringMap). > > So, MurmurHash is intended for blocks of arbitrary binary data, which may contain character data, integers, or whatever - it's designed to do such a thorough job of mixing the bits that it really doesn't matter what data types you feed it. You are corre...

On Mon, Feb 13, 2012 at 1:22 AM, Jay Foad <jay.foad at gmail.com> wrote: > On 13 February 2012 00:59, Talin <viridia at gmail.com> wrote: > > Here's my latest version of Hashing.h, which I propose to add to > llvm/ADT. > > Comments welcome and encouraged. > > > /// Adapted from MurmurHash2 by Austin Appleby > > Just out of curiosity, why not

...addImpl(StrVal.data(), StrVal.size()); > } > > I'm contradicting my stance above about not caring about the implementation :), but is MurmurHash a good hash for string data? The Bernstein hash function works really well and is much cheaper to compute than Murmur. It is used by HashString (and thus by StringMap). > > So, MurmurHash is intended for blocks of arbitrary binary data, which may contain character data, integers, or whatever - it's designed to do such a thorough job of mixing the bits that it really doesn't matter what data types you feed it. You are corr...

On Mon, Mar 16, 2015 at 11:00 PM, David Blaikie <dblaikie at gmail.com> wrote: > > > On Mon, Mar 16, 2015 at 10:52 PM, Davide Italiano <davide at freebsd.org> > wrote: >> >> On Mon, Mar 16, 2015 at 1:54 AM, Davide Italiano <davide at freebsd.org> >> wrote: >> > >> > Shankar's parallel for per-se didn't introduce any

In the midst of making TableGen Inits unique, I've run into some very odd DenseMap behavior. I converted the TernOpInit to use a factory method that uses a DenseMap to unique objects. I have defined a DenseMapInfo for std::string that uses HashString from StringExtras.h. const TernOpInit *TernOpInit::get(TernaryOp opc, const Init *lhs, const Init *mhs, const Init *rhs, RecTy *Type) { #define WORKS #ifdef WORKS typedef std::pair< std::pair< std::pair<std...

...wrote: > > >/ I'm contradicting my stance above about not caring about the > />/ implementation :), but is MurmurHash a good hash for string data? > />/ The Bernstein hash function works really well and is much cheaper to > />/ compute than Murmur. It is used by HashString (and thus by StringMap). > / > > If you want a good string hashing function, CityHash is by a fair margin > the best one out there. Look at the comparison done by Craig, Howard, and > several others when discussing what hashing function to use for libc++. > > The only downsi...

...t, or are you just guessing from the length of the code? The benchmarks I've seen say the opposite: http://code.google.com/p/smhasher/wiki/MurmurHash3#Bulk_speed_test,_hashing_an_8-byte-aligned_256k_block and http://code.google.com/p/cityhash/source/browse/trunk/README. > It > is used by HashString (and thus by StringMap). > >   // Add a possibly unaligned sequence of bytes. >   void addImpl(const char *I, size_t Length) { > > This should probably be moved out of line to avoid code bloat. > > Overall, the design of the class is making sense to me!  Thanks for tackling...

...()); >> } >> >> I'm contradicting my stance above about not caring about the >> implementation :), but is MurmurHash a good hash for string data? >> The Bernstein hash function works really well and is much cheaper to >> compute than Murmur. It is used by HashString (and thus by StringMap). >> >> So, MurmurHash is intended for blocks of arbitrary binary data, which may > contain character data, integers, or whatever - it's designed to do such a > thorough job of mixing the bits that it really doesn't matter what data > types you...