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The paper Why Programmer-specified Aliasing is a Bad Idea[0] evaluated the effectiveness of restrict in 2004. They found that adding optimal restrict annotation
by tjalfi 5y ago
The paper Why Programmer-specified Aliasing is a Bad Idea[0] evaluated the effectiveness of restrict in 2004. They found that adding optimal restrict annotations provided only a minor performance improvement, on average less than 1% across the SPEC2000 benchmarks.
[0] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.94.140&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.94....
- dralley 5y agoHow much of this is because nobody puts effort into these optimizations? The Rust compiler has repeatedly found critical bugs in LLVM's restrict / noalias support, bugs that would impact C / C++ as well if any real-world C / C++ programs actually used it. If compilers produce straight-up broken code in these situations, I can only imagine they're not putting a lot of effort into these optimization strategies.
- tjalfi 5y ago> How much of this is because nobody puts effort into these optimizations? restrict is rare in C and C++ but common in Fortran; array parameters in Fortran aren't allowed to alias. Intel and IBM both have great Fortran compilers so I would expect their C and C++ compilers to have good support for restrict.