[all-commits] [llvm/llvm-project] ea5262: [flang][runtime] Use dumber but faster check for l...

[Peter Klausler via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: ea5262ffc95a767cb5a4b0ea6f04857e4aa00c46
      https://github.com/llvm/llvm-project/commit/ea5262ffc95a767cb5a4b0ea6f04857e4aa00c46
  Author: Peter Klausler <pklausler at nvidia.com>
  Date:   2025-09-23 (Tue, 23 Sep 2025)

  Changed paths:
    M flang-rt/include/flang-rt/runtime/io-stmt.h
    M flang-rt/lib/runtime/io-stmt.cpp

  Log Message:
  -----------
  [flang][runtime] Use dumber but faster check for list-directed repeti… (#159867)

…tion

When scanning list-directed input for nulls and repetition counts, the
current library depends on having each record be prescanned for the
presence of asterisk characters. It turns out that the overhead of
calling memchr(...,'*',...) on each record doesn't pay off, especially
on systems without SIMD-vectorized memchr implementations -- even on
those, it's faster (about 10%) to just scan ahead for asterisks when
decimal digits are encountered. Only when an asterisk is present, which
is not common, should we then bother to convert the digits to their
integer value.



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications