On the platform specificity of STM instrumentation mechanisms

Supporting atomic blocks (e.g., Transactional Memory (TM)) can have far-reaching effects on language design and implementation. While much is known about the language-level semantics of TM and the performance of algorithms for implementing TM, little is known about how platform characteristics affect the manner in which a compiler should instrument code to achieve efficient transactional behavior. We explore the interaction between compiler instrumentation and the performance of transactions. Through evaluation on ARM/Android, SPARC/Solaris, IA32/Linux and IA32/MacOS, we show that the compiler must consider the platform when determining which analyses, transformations, and optimizations to perform. Implementation issues include how TM library code is reached, how per-thread TM metadata is stored and accessed, and how a library switches between modes of operation. We also show that different platforms favor different TM algorithms, through the introduction of a new TM algorithm for the ARM processor. Our findings will affect compiler and TM library designers: to achieve peak performance for transactions, the compiler must perform platform-dependent analysis, transformation, and optimization, and the interface to the TM library must differ according to platform.