How to conditionally specify C compiler defines in bazel? - build

Question

I am trying to convert Makefile build into bazel, and need to reproduce the following condition to specify CPU capabilities defines for C code compilation:
HAVE_AVX2 := $(shell grep avx2 /proc/cpuinfo)
ifdef HAVE_AVX2
$(info Checking for AVX support... AVX and AVX2)
CFLAGS += -DRTE_MACHINE_CPUFLAG_AVX -DRTE_MACHINE_CPUFLAG_AVX2
else
HAVE_AVX := $(shell grep avx /proc/cpuinfo)
ifdef HAVE_AVX
$(info Checking for AVX support... AVX)
CFLAGS += -DRTE_MACHINE_CPUFLAG_AVX
else
$(info Checking for AVX support... no)
endif
endif
Is it possible to implement such conditional in bazel? From what I have found, cc_library has defines and copts where I could use a select function, but I cannot understand what kind of condition I can use inside of select.

Answer 1

Take a look at https://docs.bazel.build/versions/master/be/general.html#config_setting.
Generally, you do something like
config_setting(
name = "avx2",
values = {
"define": "avx2=yes"
}
)
and the you can select on :avx2 condition:
cc_library(...
copts = select({":avx2":[...], ...})
and run bazel with
bazel build --define avx2=yes ...