More Work items - More Resource usage?

I have explained this multiple times in different threads, so I will just post some of the existing discussions:

What about BRAM blocks when my thread uses private memory? Would the private memory allocated for one item gets reused? What happens when I use attributes like SIMD and CU? For eg:- In the case of GEMM example, doubling the SIMD attribute doubles the BRAM usage. I can understand that doubling of BRAM blocks with increasing CU attribute but why would SIMD attribute increase BRAM. Is it because of the local memory replication? Is there any attribute to set a limit for the replication of local memory?

Private memory is generally implemented using registers and does not use Block RAMs. Large local memory buffers are implemented using Block RAMs. CU increases Block RAM usage with the CU factor since it replicates the whole pipeline. The effect of SIMD is not straightforward. If accesses to your local buffer are coalesced under the presence of SIMD, which means the number of ports to that buffer does not change, then replication factor stays the same and Block RAM utilization hardly changes. If, however, such accesses are not consecutive and cannot be coalesced, then using SIMD which increase the number of ports by the SIMD factor and can significantly increase the replication factor. Block RAM replication factor depends on the number of barriers in the kernel, number of accesses to the buffer, and number of work-groups the compiler decides to run simultaneously. The latter cannot be directly controlled by the user. Some attributes are provides to control banking and number of ports for local memory buffers. You can find the details in "Intel FPGA SDK for OpenCL Best Practices Guide, Section 7.5 - Optimizing Accesses to Local Memory by Controlling the Memory Replication Factor".

Number of work groups running simultaneously depends on the compiler? Is it not the number of compute units?