We saw mixed results from this on LNT, including some major regressions. For example, on x86_64, SingleSource/Benchmarks/Shootout-C++/hash2 regressed 18.5% at -O3 and over 20% at -Os.
Is this expected? > On 2016-Jul-11, at 15:02, Eric Fiselier via cfe-commits > <cfe-commits@lists.llvm.org> wrote: > > Author: ericwf > Date: Mon Jul 11 17:02:02 2016 > New Revision: 275114 > > URL: http://llvm.org/viewvc/llvm-project?rev=275114&view=rev > Log: > Don't compute modulus of hash if it is smaller than the bucket count. > > This cleans up a previous optimization attempt in hash, and results in > additional performance improvements over that previous attempt. Additionally > this new optimization does not hinder the power of 2 bucket count > optimization. > > Modified: > libcxx/trunk/include/__hash_table > > Modified: libcxx/trunk/include/__hash_table > URL: > http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__hash_table?rev=275114&r1=275113&r2=275114&view=diff > ============================================================================== > --- libcxx/trunk/include/__hash_table (original) > +++ libcxx/trunk/include/__hash_table Mon Jul 11 17:02:02 2016 > @@ -90,7 +90,8 @@ inline _LIBCPP_INLINE_VISIBILITY > size_t > __constrain_hash(size_t __h, size_t __bc) > { > - return !(__bc & (__bc - 1)) ? __h & (__bc - 1) : __h % __bc; > + return !(__bc & (__bc - 1)) ? __h & (__bc - 1) : > + (__h < __bc ? __h : __h % __bc); > } > > inline _LIBCPP_INLINE_VISIBILITY > @@ -2201,8 +2202,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc> > if (__nd != nullptr) > { > for (__nd = __nd->__next_; __nd != nullptr && > - (__hash == __nd->__hash_ > - || __constrain_hash(__nd->__hash_, __bc) == __chash); > + __constrain_hash(__nd->__hash_, __bc) == __chash; > __nd = > __nd->__next_) > { > if ((__nd->__hash_ == __hash) && key_eq()(__nd->__value_, > __k)) > @@ -2231,8 +2231,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc> > if (__nd != nullptr) > { > for (__nd = __nd->__next_; __nd != nullptr && > - (__hash == __nd->__hash_ > - || __constrain_hash(__nd->__hash_, __bc) == __chash); > + __constrain_hash(__nd->__hash_, __bc) == __chash; > __nd = > __nd->__next_) > { > if ((__nd->__hash_ == __hash) && key_eq()(__nd->__value_, > __k)) > > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
