Compile multi-architecture code using Agner's Vector Class Library

Question

How can I create a library that will dynamically switch between SSE, AVX, and AVX2 code paths depending on the host processor/OS? I am using Agner Fog's VCL (Vector Class Library) and compiling with GCC for Linux.

Answer 1

See the section "Instruction sets and CPU dispatching" in the manual to the Vector Class Library. In that section Agner writes

The file dispatch_example.cpp shows an example of how to make a CPU dispatcher that selects the appropriate code version.

Read the source code to distpatch_example.cpp. At the start of the file you should see the comment

# Compile dispatch_example.cpp five times for different instruction sets:
| g++ -O3 -msse2    -c dispatch_example.cpp -od2.o
| g++ -O3 -msse4.1  -c dispatch_example.cpp -od5.o
| g++ -O3 -mavx     -c dispatch_example.cpp -od7.o
| g++ -O3 -mavx2    -c dispatch_example.cpp -od8.o
| g++ -O3 -mavx512f -c dispatch_example.cpp -od9.o
| g++ -O3 -msse2 -otest instrset_detect.cpp d2.o d5.o d7.o d8.o d9.o
| ./test

The file instrset_detect.cpp. You should read the source code to this also. This is what calls CPUID.

Here is a summary of some, but not all of, my questions and answers on CPU dispatchers.