id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
13180	Loop vectorisation using boost multi_array	Nicolas Barrier <nicolas.barrier@…>	Ronald Garcia	"Dear all

I am trying to optimize a huge code that uses boost multi-arrays. And when I compile the code with the ''-qopt-report=2 -qopt-report-phase=vec'' options, I notice in the compilation report that most loops are not vectorized.

I thus made a simple program to understand why, and I noticed that a loop that uses C array is vectorized, while the same loop using boost multi array is not (see test_vector.cpp) (see attached .cpp file). I get the following message:

{{{
LOOP BEGIN at test_vector.cpp(29,5)
   remark #15520: loop was not vectorized: loop with multiple exits cannot be vectorized unless it meets search loop idiom criteria
LOOP END
}}}

A way to overcome this would be to use the data pointer in combination with the {{{#pragma ivdep}}} statement, but this becomes complicated when working on multimensional arrays.

I thus would like to know if I am doing something wrong (for instance in the boost array initialisation), and if there is a way to fix this?

I am using the icpc compiler, version 16.0.4, with boost library version 1.65. The program is compiled as follows:

{{{
icpc -Ilibs/cpp/boost_1_65_0/ -O3 -qopt-report=2 -qopt-report-phase=vec test_vector.cpp
}}}

Thanks a lot

Nicolas Barrier"	Support Requests	new	To Be Determined	multi_array	Boost 1.65.0	Optimization