When building Python 3.6.X and later with icc (18.0.0.128 or
18.0.1.163), there's an error building the _sha3 module with any
optimization level other than -O0:

building '_sha3' extension
icc -pthread -fPIC -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3
-Wall -Wstrict-prototypes -std=c99 -Wextra -Wno-unused-parameter
-Wno-missing-field-initializers -fp-model strict -I./Include -I.
-I/usr/local/include
-I/derp/Python-3.6.4/Include
-I/derp/Python-3.6.4 -c
/derp/Python-3.6.4/Modules/_sha3/
sha3module.c -o
build/temp.linux-x86_64-3.6/derp/Python-3.6.4/Modules/_sha3/sha3module.o
": internal error: ** The compiler has encountered an unexpected problem.
** Segmentation violation signal raised. **
Access violation or stack overflow. Please contact Intel Support for assistance.

compilation aborted for
/derp/Python-3.6.4/Modules/_sha3/sha3module.c
(code 4)
...
[ jlselogin2: Python-3.6.4 ]$

if I drop to -O0, compilation works every time. I haven't found
disabling any particular set of optimizations to be useful in
obtaining a successful build.
...
[ jlselogin2: Python-3.6.4 ]$

dropping to -O0, compilation works every time. I haven't found
disabling any particular set of optimizations to be useful in
obtaining a successful build with icc.

 Intel has been notified and a bug filed as this is really a compiler bug. On the Python side, it does not appear possible to use Modules/Setup to drop the optimization level for just _sha3 and I'm hunting for a workaround.