Automatically Harnessing Sparse Acceleration

Sparse linear algebra is central to many scientific programs, yet compilers fail to optimize it well. High-performance libraries are available, but adoption costs are significant. Moreover, libraries tie programs into vendor-specific software and hardware ecosystems, creating non-portable code. In this paper, we develop a new approach based on our specification Language for implementers of Linear Algebra Computations (LiLAC). Rather than requiring the application developer to (re)write every program for a given library, the burden is shifted to a one-off description by the library implementer. The LiLAC-enabled compiler uses this to insert appropriate library routines without source code changes. LiLAC provides automatic data marshaling, maintaining state between calls and minimizing data transfers. Appropriate places for library insertion are detected in compiler intermediate representation, independent of source languages. We evaluated on large-scale scientific applications written in FORTRAN; standard C/C++ and FORTRAN benchmarks; and C++ graph analytics kernels. Across heterogeneous platforms, applications and data sets we show speedups of 1.1$\times$ to over 10$\times$ without user intervention.Comment: Accepted to CC 202

Titanium hydroamination catalysts bearing a 2-aminopyrrolinato spectator ligand: monitoring the individual reaction steps

A series of new titanium half sandwich complexes, containing a 2-aminopyrrolinato ligand {NXylN}− as the ancillary ligand, have been prepared and are shown to be pre-catalysts for the hydroamination of alkynes. The coordination of {NXylN}− to titanium was achieved by reaction of [Cp*TiMe3] with the protioligand NXylNH giving [Cp*Ti(NXylN)(Me)2] (1). Upon reaction of complex 1 with an excess of tert-butylamine, the imido complex [Cp*Ti(NXylN)(NtBu)(NH2tBu)] (2) was formed. The latter provided the preparative entry to the synthesis of a range of N-aryl substituted imido complexes. Imido ligand exchange with 2,6-dimethylaniline, 2,4,6-trimethylaniline as well as 2,6-diisopropylaniline gave the corresponding arylimido complexes 3–5 in clean reactions. Reaction of the titanium imido complex [Cp*Ti(NXylN)(NtBu)(NH2tBu)] 2 with terminal arylacetylenes, such as phenylacetylene and tolylacetylene, led to C–H activation and the formation of alkynyl/amido complexes, whereas the arylimido complexes 3 and 5 cleanly underwent {2 + 2} cycloaddition, giving the azatitanacyclobutene derivatives. A single-crystal X-ray structure analysis of the azatitanacyclobutene [Cp*Ti(NXylN){κ2N(2,6-C6H3Me2)CTolCH}] (11) provided the first crystallographically characterized Markovnikov cycloaddition product of an imidotitanium complex with a terminal alkyne. The mechanistic aspects of the hydromanination of alkynes with the new Ti half sandwich complexes were studied and established a reversible {2 + 2} cycloaddition step and the cleavage of the metallacyclic intermediate as the rate determining step in the catalytic cycle. The titanium half sandwich imido complexes were found to be active catalysts for the inter- and intramolecular hydroamination of a broad range of alkynes and ω-aminoalkynes