Low overhead speculative selection of hot traces in a caching dynamic translator

Abstract

A method and apparatus for selecting hot traces for translation and/or optimization is described in the context of a caching dynamic translator. The code cache stores hot traces. Profiling is done at locations that satisfy a start-of-trace condition, e.g., the targets of backward taken branches. A hot target of a backward taken branch is speculatively identified as the beginning of a hot trace, without the need to profile the blocks that make up the trace. The extent of the speculatively selected hot trace is determined by an end-of-trace condition, such as a backward taken branch or a number of interpreted or native instructions. The interpreter is augmented with a mode in which it emits native instructions that are cached. A trace is cached by identifying a hot start of a trace and then continuing interpretation while storing the emitted native instruction stream until an end-of-trace condition is met.