What does it mean by "loop is parallelizable"

Accelerated Computing HPC Compilers Legacy PGI Compilers
1

When compiled the program,
the compiler would indicate somewhere “loop is parallelizable”.

What does it mean ? Does it mean the compiler detect this loop
as parallelizable and parallelize it automatically or just detect it but not parallelize it ?

Also, if I declare “routine seq” in ahead of a function and leave
all the function code unmodified, I guess all the loops inside the function
would not be parallelized by the compiler automatically, is it correct ?

Thanks.

2

Loop is parallelizable means that it could be executed in parallel threads
safely - it is a comment on the independency of each iteration.

-Mconcur

will auto-parallelize those loops that are safe to run in parallel threads.

You can also use OpenACC to designate areas that will run parallel,
whether or not the compiler determines the region is ‘safe’ to auto
parallelize.

dave