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Compiler-specific Features
If the intention is to multiply a matrix that is not a multiple of four in size, for example
an n * n matrix, #pragma unroll (m) might be used instead, where m is some value such
that n is an integral multiple of m.
See also
• --diag_warning=optimizations on page 2-31
• -Onum on page 2-66
• -Otime on page 2-69
• --[no_]vectorize on page 2-91
• #pragma unroll_completely
• Optimizing loops on page 4-4 in the Compiler User Guide.
4.6.22 #pragma unroll_completely
This pragma instructs the compiler to completely unroll a loop. It has an effect only if
the compiler can determine the number of iterations the loop has.
Note
Both vectorized and non vectorized loops can be unrolled using #pragma
unroll_completely. That is, #pragma unroll_completely applies to both --no_vectorize
and --vectorize.
Usage
When compiling at -O3 -Otime, the compiler automatically unrolls loops where it is
beneficial to do so. You can use this pragma to request that the compiler completely
unroll a loop that has not automatically been unrolled completely.
Note
Use this #pragma only when you have evidence, for example from
--diag_warning=optimizations, that the compiler is not unrolling loops optimally by
itself.
Restrictions
#pragma unroll_completely can only be used immediately before a for loop, a while
loop, or a do ... while loop.
Using #pragma unroll_completely on an outer loop can prevent vectorization. On the
other hand, using #pragma unroll_completely on an inner loop might help in some cases.
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