[flang-rt] Simplify INDEX with len-1 SUBSTRING. #137889
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The len-1 case is noticeably slower than gfortran's straightforward implementation https://github.com/gcc-mirror/gcc/blob/075611b646e5554ae02b2622061ea1614bf16ead/libgfortran/intrinsics/string_intrinsics_inc.c#L253 This change speeds up a simple microkernel by 37% on icelake.
klausler
reviewed
Apr 29, 2025
flang-rt/lib/runtime/character.cpp
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| if (wantLen == 1) { | ||
| // Trivial case for single character lookup. | ||
| // We can use simple forward search. | ||
| CHAR ch = want[0]; |
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This could just become a call to std::memchr() for KIND==1.
For other kinds, please add braced initialization to the two declarations here.
klausler
approved these changes
Apr 30, 2025
flang-rt/lib/runtime/character.cpp
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| // We can use simple forward search. | ||
| CHAR ch{want[0]}; | ||
| if constexpr (std::is_same_v<CHAR, char>) { | ||
| auto pos{reinterpret_cast<const CHAR *>( |
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Save a line with if (auto pos{}) { ...
IanWood1
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May 6, 2025
The len-1 case is noticeably slower than gfortran's straightforward implementation https://github.com/gcc-mirror/gcc/blob/075611b646e5554ae02b2622061ea1614bf16ead/libgfortran/intrinsics/string_intrinsics_inc.c#L253 This change speeds up a simple microkernel by 37% on icelake.
GeorgeARM
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May 7, 2025
The len-1 case is noticeably slower than gfortran's straightforward implementation https://github.com/gcc-mirror/gcc/blob/075611b646e5554ae02b2622061ea1614bf16ead/libgfortran/intrinsics/string_intrinsics_inc.c#L253 This change speeds up a simple microkernel by 37% on icelake.
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The len-1 case is noticeably slower than gfortran's straightforward
implementation https://github.com/gcc-mirror/gcc/blob/075611b646e5554ae02b2622061ea1614bf16ead/libgfortran/intrinsics/string_intrinsics_inc.c#L253
This change speeds up a simple microkernel by 37% on icelake.