https://bazel.build/docs/user-manual#build-semantics shows that bazel build -c opt is the same as bazel build --copt="-O2" --copt="-DNDEBUG"

Instead, we optimize for size by using bazel build --copt="-Os". This uses most of -O2 optimization except the ones list here:

-falign-functions  -falign-jumps
-falign-labels  -falign-loops
-fprefetch-loop-arrays  -freorder-blocks-algorithm=stc

Out of these -fprefetch-loop-arrays doesn't work with -Os. All others work without increasing the wheel size. The final wheel size after this change is 84MB.

Reference: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html