22% degradation seen in embench:matmult-int

[Visda.Vokhshoori@microchip.com]

Embench is used for benchmarking on embedded devices.
This one project matmult-int has a function Multiply.  It’s a matrix multiplication for 20 x 20 matrix.
The device is a ATSAME70Q21B which is Cortex-M7
The compiler is arm branch based on GCC version 13
We are compiling with O3 which has loop-interchange pass on by default.

When we compile with -fno-loop-interchange we get all 22% back plus 5% speed up.

When we do the loop interchange on the one loop nest that get interchanged it is slightly (.7%) faster.

Has anyone else seen large degradation as a result of loop interchange?

Thanks