Low Level Virtual Machine Compiler Research Articles

REDUCER: Elimination of Repetitive Codes for Accelerated Iterative Compilation

Low Level Virtual Machine (LLVM) is a widely adopted open source compiler providing numerous optimization opportunities. The discovery of the best optimization sequence in this large space is done via iterative compilation, which incurs substantial overheads, especially for big data applications operating on high volume and variety datasets. The large search space is mostly comprised of identical codes generated via different optimizations. However, no mechanism is implemented inside the LLVM compiler to suppress the redundant testings. In this regard, this paper proposes REDUCER for eliminating the identical code executions by performing Intermediate Representation (IR) level comparisons. REDUCER has been tested using the well-accepted MiCOMP technique in LLVM 3.8 and 9.0 compiler, with embedded (cBench) and big data workloads. In comparison to MiCOMP 19.5 k experiments, REDUCER lowers the experiment count up to 327, i.e. 98 %, and on average to 4 375, i.e. 77 %, for cBench (LLVM-3.8). Similarly, for LLVM-9.0 the reductions are up to 1 931, i.e. 90 %, and on average 5 863, i.e. 69.9 %. Due to the significant experiment reduction, for embedded workloads, the iterative compilation is up to 58.6× and on average 4.1× faster with REDUCER (LLVM-3.8) than MiCOMP, whereas, with REDUCER (LLVM-9.0) the compilation is up to 8.5× and on average 2.9× faster. Moreover, REDUCER is found to be scalable and efficient for big data workloads where the iterative compilation is reduced to few days, as code is compared one time only for a single application tested on multiple datasets.

A dynamic approach to detecting, eliminating and fixing memory leaks

This paper presents a dynamic approach to detecting, eliminating and fixing memory leaks. With our approach, a program to be analyzed is instrumented before its execution. Dynamic symbolic execution is employed so as to expose memory leaks occurring in all execution paths. During the program execution, information about each allocated memory area is updated when corresponding statements are executed. Based on this information, a back-end leak checker records the changes of variables pointing to each memory area, detects memory leaks and deallocates leaked memory areas. After the program execution, a fixed program containing deallocation statements is generated. We have implemented our approach in a tool called DEF_LEAK based on Low Level Virtual Machine compiler infrastructure. Experiments show that DEF_LEAK can detect more leaks than the existing dynamic detection tools for programs with user inputs. Moreover, DEF_LEAK is more effective for helping programmers understand and fix memory leaks than other detection tools.

Описание подхода к разработке обфусцирующего компилятора

Nowadays protecting intellectual property rights for created software is very important because of many competing companies and ubiquitous piracy. The powerful technique for this protection is to obfuscate program code. This paper describes an approach for developing an obfuscation tool based on a compiler infrastructure. Using the compiler infrastructure is beneficial as during compilation we have the complete information about the compiled program for free and we do not need to solve problems like correct disassembling, new target support etc. We have formulated the efficiency criteria for an obfuscating technique: an obfuscation transformation should obfuscate both control flow and data flow simultaneously. The main feature of the described approach is using the set of transformations, which mask the various aspects of the obfuscated application. Together, this set provides the strong protection against the static analysis. Opaque predicates insertions, flattening and increasing indirection transformation are the most efficient transformations. Also we have formulated the compiler infrastructure requirements that need to hold for successfully implementing an obfuscating compiler using this infrastructure. The essential requirements are complied with LLVM (low level virtual machine) compiler infrastructure.