[C++] [Parquet] Use std::count in parquet ColumnReader #39398
Description
Describe the enhancement requested
I've found that for-loop here
arrow/cpp/src/parquet/column_reader.cc
Lines 1055 to 1073 in 7c3480e
transforms into
0xc0c2f0 <ReadLevels()+96> inc %rdx
0xc0c2f3 <ReadLevels()+99> cmp %rax,%rdx
0xc0c2f6 <ReadLevels()+102> jge 0xc0c30c <ReadLevels()+124>
0xc0c2f8 <ReadLevels()+104> cmp %cx,(%r14,%rdx,2)
0xc0c2fd <ReadLevels()+109> jne 0xc0c2f0 <ReadLevels()+96>
0xc0c2ff <ReadLevels()+111> incq 0x0(%rbp)
0xc0c303 <ReadLevels()+115> mov (%rbx),%rax
0xc0c306 <ReadLevels()+118> jmp 0xc0c2f0 <ReadLevels()+96>
That means that it uses iteration element by element and changes reference with incq
I think that the reason is that values_to_read and num_def_levels are not set as restrict. So the compiler can not optimize this to a more efficient way(for example using simd)
On my flamegraph this part showed ~10% of time spent
Component(s)
C++, Parquet