Performance with C++

as written in Numeric / Math / Linear Algebra, calculation with denormals or non-numbers slows down performance - even when not signalled.
it might be interesting to abort a calculation, e.g. a matrix/vector multiplication, with first occurence of NaN - or with one of the other conditions ..

Ofek Shilon held the talk Optimization Remarks - Helping the Compiler to Generate Better Code at CppCon 2022. Here his PDF slides. Here also slides of a sligthly older talk on the same topic: https://www.slideshare.net/ofekshilon/optview2-c-on-sea-2022

references from his slides:

• llvm-opt-report
  • https://reviews.llvm.org/D25262
  • https://github.com/llvm/llvm-project/tree/main/llvm/tools/llvm-opt-report
  • https://llvm.org/docs/Remarks.html
  • debian package llvm-14-tools
  • clang compiler switch -fsave-optimization-record
• opt-viewer / optview2
  • https://github.com/llvm/llvm-project/tree/main/llvm/tools/opt-viewer (origin)
  • https://github.com/OfekShilon/optview2 produces much better output
  • opt-viewer.py –output-dir <htmls folder> –source-dir <repo> <yamls folder>
• Clobbered by store
  • use compiler specific keyword __restrict or HEDLEY_RESTRICT
    • https://github.com/nemequ/Hedley
• Clobbered by call or load
  • function attribute __attribute__((const)) or HEDLEY_CONST
    • const functions are not using any saved/global state; thus free of side-effects
    • compiler can remove repeated invokations
    • const is stronger than pure
  • function attribute __attribute__((pure)) or HEDLEY_PURE
    • see https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html for pure and const
    • hedley doc is much easier to understand / discriminate:
      • https://nemequ.github.io/hedley/api-reference.html#HEDLEY_PURE
      • https://nemequ.github.io/hedley/api-reference.html#HEDLEY_CONST
  • function parameter attribute __attribute__((noescape)) or HEDLEY_NO_ESCAPE
    • see https://clang.llvm.org/docs/AttributeReference.html#noescape
• Talk Compiler-assisted performance analysis of Adam Nemet
  • https://www.youtube.com/watch?v=qq0q1hfzidg

• Denis Bakhalov - EasyPerf!
  • https://easyperf.net/
• Johnny’s Software Lab
  • https://johnnysswlab.com/