Compiler analysis for trace-level speculative multithreaded architectures

Trace-level speculative multithreaded processors exploit trace-level speculation by means of two threads working cooperatively. One thread, called the speculative thread, executes instructions ahead of the other by speculating on the result of several traces. The other thread executes speculated traces and verifies the speculation made by the first thread. In this paper, we propose a static program analysis for identifying candidate traces to be speculated. This approach identifies large regions of code whose live-output values may be successfully predicted. We present several heuristics to determine the best opportunities for dynamic speculation, based on compiler analysis and program profiling information. Simulation results show that the proposed trace recognition techniques achieve on average a speed-up close to 38% for a collection of SPEC2000 benchmarks.Peer ReviewedPostprint (published version

Trace-level reuse

Trace-level reuse is based on the observation that some traces (dynamic sequences of instructions) are frequently repeated during the execution of a program, and in many cases, the instructions that make up such traces have the same source operand values. The execution of such traces will obviously produce the same outcome and thus, their execution can be skipped if the processor records the outcome of previous executions. This paper presents an analysis of the performance potential of trace-level reuse and discusses a preliminary realistic implementation. Like instruction-level reuse, trace-level reuse can improve performance by decreasing resource contention and the latency of some instructions. However, we show that trace-level reuse is more effective than instruction-level reuse because the former can avoid fetching the instructions of reused traces. This has two important benefits: it reduces the fetch bandwidth requirements, and it increases the effective instruction window size since these instructions do not occupy window entries. Moreover, trace-level reuse can compute all at once the result of a chain of dependent instructions, which may allow the processor to avoid the serialization caused by data dependences and thus, to potentially exceed the dataflow limit.Peer ReviewedPostprint (published version

Proving Safety with Trace Automata and Bounded Model Checking

Loop under-approximation is a technique that enriches C programs with additional branches that represent the effect of a (limited) range of loop iterations. While this technique can speed up the detection of bugs significantly, it introduces redundant execution traces which may complicate the verification of the program. This holds particularly true for verification tools based on Bounded Model Checking, which incorporate simplistic heuristics to determine whether all feasible iterations of a loop have been considered. We present a technique that uses \emph{trace automata} to eliminate redundant executions after performing loop acceleration. The method reduces the diameter of the program under analysis, which is in certain cases sufficient to allow a safety proof using Bounded Model Checking. Our transformation is precise---it does not introduce false positives, nor does it mask any errors. We have implemented the analysis as a source-to-source transformation, and present experimental results showing the applicability of the technique

Test Case Purification for Improving Fault Localization

Finding and fixing bugs are time-consuming activities in software development. Spectrum-based fault localization aims to identify the faulty position in source code based on the execution trace of test cases. Failing test cases and their assertions form test oracles for the failing behavior of the system under analysis. In this paper, we propose a novel concept of spectrum driven test case purification for improving fault localization. The goal of test case purification is to separate existing test cases into small fractions (called purified test cases) and to enhance the test oracles to further localize faults. Combining with an original fault localization technique (e.g., Tarantula), test case purification results in better ranking the program statements. Our experiments on 1800 faults in six open-source Java programs show that test case purification can effectively improve existing fault localization techniques

Source code patches from dynamic analysis

Dynamic analysis can identify improvements to programs that cannot feasibly be identified by static analysis; concurrency improvements are a motivating example. However, mapping these dynamic-analysis-based improvements back to patch-like source-code changes is non-trivial. We describe a system, Scopda, for generating source-code patches for improvements identified by execution-trace-based dynamic analysis. Scopda uses a graph-based static program representation (abstract program graph, APG), containing inter-procedural control flow and local data flow information, to analyse and transform static source-code. We demonstrate Scopda's ability to generate sensible source code patches for Java programs, though it is fundamentally language agnostic.The first author was funded by the Engineering and Physical Sciences Research Council (EPSRC), the Cambridge Trusts, and the University of Cambridge Department of Computer Science and Technology

Evaluation of Naa Laboratory Results in Inter-comparison on Determination of Trace Elements in Food and Environmental Samples

Inter-comparison program is a good tool for improving quality and to enhance the accuracy and precision of theanalytical techniques. By participating in this program, laboratories could demonstrate their capability andensuring the quality of analysis results generated by analytical laboratories. The Neutron Activation Analysis(NAA) laboratory at National Nuclear Energy Agency of Indonesia (BATAN), Nuclear Technology Center forMaterials and Radiometry-PTNBR laboratory participated in inter-comparison tests organized by NAA workinggroup. Inter-comparison BATAN 2009 was the third inter-laboratory analysis test within that project. Theparticipating laboratories were asked to analyze for trace elements using neutron activation analysis as theprimary technique. Three materials were distributed to the participants representing foodstuff, and environmentalmaterial samples. Samples were irradiated in rabbit facility of G.A. Siwabessy reactor with neutron flux ~ 1013n.cm-2.s-1, and counted with HPGe detector of gamma spectrometry. Several trace elements in these sampleswere detected. The accuracy and precision evaluation based on International Atomic Energy Agency (IAEA)criteria was applied. In this paper the PTNBR NAA laboratory results is evaluated