Fix CMake Bugs

[CascadingRadium]

• Fix default logic when no optimization level is set, set to "generic".
• Fix c_api library linkage and installation in case of optimization levels.
  • faiss_c -> faiss in case of generic.
  • faiss_c_avx2 -> faiss_avx2 in case of AVX2.

[abhinavdangeti]

Not sure I follow this, don't we need to do call RUNTIME DESTINATION and INCLUDES DESTINATION for all FAISS_OPT_LEVELs?

[CascadingRadium]

faiss/faiss/CMakeLists.txt

Line 428 in 95f5e7e

if(FAISS_OPT_LEVEL STREQUAL "generic")

this check for "generic" is there for the "faiss" sub project as well.
Mainly, if we use "avx2", we unnecessarily install the regular faiss_c as well.

[abhinavdangeti]

I think @ceejatec should weigh in on this too.

[abhinavdangeti]

And why are we getting rid of this - in our current builds we do produce libfaiss with the avx2 suffix when FAISS_OPT_LEVEL is set to avx2.

[CascadingRadium]

basically earlier we had

• faiss_c.so -> faiss.so, faiss_avx2.so, faiss_avx512.so etc.

in the latest upstream

• faiss_c_avx2.so -> faiss_avx2.so
• faiss_c.so -> faiss.so
• faiss_c_avx512.so -> faiss_avx512.so

basically there are specialized _c libraries for each corresponding
faiss library.

[CascadingRadium]

faiss/c_api/CMakeLists.txt

Line 45 in 95f5e7e

target_link_libraries(faiss_c_avx2 PRIVATE faiss_avx2)

[abhinavdangeti]

Right, and this is the bit I'm concerned with, it seems we setup faiss_c and faiss_avx2 currently ..

root@se2207-ubu20:~# ls -lart /opt/couchbase/lib/libfaiss_*
-rw-r--r-- 1 couchbase couchbase   204064 Mar 30  2010 /opt/couchbase/lib/libfaiss_c.so
-rw-r--r-- 1 couchbase couchbase 37985928 Mar 30  2010 /opt/couchbase/lib/libfaiss_avx2.so
root@se2207-ubu20:~# ldd /opt/couchbase/lib/libfaiss_c.so
	linux-vdso.so.1 (0x00007ffd65dd8000)
	libfaiss_avx2.so => /opt/couchbase/lib/libfaiss_avx2.so (0x00007f0bfb6ed000)
	libstdc++.so.6 => /opt/couchbase/lib/libstdc++.so.6 (0x00007f0bfb48d000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f0bfb334000)
	libgcc_s.so.1 => /opt/couchbase/lib/libgcc_s.so.1 (0x00007f0bfb30f000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f0bfb11d000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f0bfdb6b000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f0bfb0fa000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f0bfb0f2000)
	libgomp.so.1 => /opt/couchbase/lib/libgomp.so.1 (0x00007f0bfb0a6000)

Will we not require to change anything on our build side on account of this?

[abhinavdangeti]

@CascadingRadium Per our conversation let's drop the changes from this PR that'll force us to use different ldflags downstream.