Program Reconditioning: Avoiding Undefined Behaviour When Finding and Reducing Compiler Bugs

We introduce program reconditioning, a method for allowing generation and differential testing to be used find miscompilation bugs, test-case reduction simplify bug-triggering programs, even when (a) the programming language of interest features undefined behaviour (UB) (b) no tools exist detect avoid this UB. present two based on our reconditioning idea: GLSLsmith OpenGL Shading Language (GLSL), widely-used graphics programming, WGSLsmith WebGPU (WGSL), new web-based rendering. GLSL many UBs, but unlike languages such as C C++ them automatically. While WGSL specification very limited UB, early implementations do exhibit reasons initial implementation simplicity, making it challenging test quickly eliminate unrelated bugs. Thanks we show that allow applied compilers first time, despite unavailability UB detection techniques these languages. Through large campaign, have found 24 33 bugs in compilers, respectively. experiments showing is disabled, compiler leads high rate programs appear trigger actually just feature also novel approach managing floating-point roundoff error using implemented both WGSL.