Symbolic crosschecking of floating-point and SIMD code

We present an effective technique for crosschecking an IEEE 754 floating-point program and its SIMD-vectorized version, implemented in KLEE-FP, an extension to the KLEE symbolic execution tool that supports symbolic reasoning on the equivalence between floating-point values. The key insight behind our approach is that floatingpoint values are only reliably equal if they are essentially built by the same operations. As a result, our technique works by lowering the Intel Streaming SIMD Extension (SSE) instruction set to primitive integer and floating-point operations, and then using an algorithm based on symbolic expression matching augmented with canonicalization rules. Under symbolic execution, we have to verify equivalence along every feasible control-flow path. We reduce the branching factor of this process by aggressively merging conditionals, if-converting branches into select operations via an aggressive phi-node folding transformation. We applied KLEE-FP to OpenCV, a popula...

• Type: Journal
• Year: 2011
• Where: EUROSYS
• Authors: Peter Collingbourne, Cristian Cadar, Paul H. J. Kelly
• Keywords: Computer Vision Library, EUROSYS 2011, Execution Tool, Software Engineering, Symbolic Execution