Dangerous Optimizations in C and C++ Programming Languages
summary
Compilers increasingly treat undefined behavior (UB) as a license for aggressive optimization, claiming wins from constant folding, loop‑invariant hoisting and induction‑variable rewrites but sometimes removing bounds checks or turning a finite loop into an infinite one. Concrete examples include the pointer+len overflow optimization that eliminates a bounds test at -O2 and GCC’s shifting diagnostics/flags (strict‑overflow deprecated in GCC 8). Practical mitigations shown are sanitizers (UBSan/ASan), auditing generated assembly, and a forthcoming TS6010 pointer provenance specification. Slides and code links are on the ACCU site.
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