[CI] Prune unused archs from libnccl (#8179)

* [CI] Prune unused archs from libnccl

* Put pruning logic in CI directory

* Don't use --color in grep

tests/ci_build/Dockerfile.gpu_build_centos7

@@ -15,8 +15,8 @@ RUN \
     bash Miniconda3.sh -b -p /opt/python && \
     /opt/python/bin/python -m pip install awscli && \
     # CMake
-    wget -nv -nc https://cmake.org/files/v3.14/cmake-3.14.0-Linux-x86_64.sh --no-check-certificate && \
-    bash cmake-3.14.0-Linux-x86_64.sh --skip-license --prefix=/usr
+    wget -nv -nc https://cmake.org/files/v3.18/cmake-3.18.0-Linux-x86_64.sh --no-check-certificate && \
+    bash cmake-3.18.0-Linux-x86_64.sh --skip-license --prefix=/usr
 
 # NCCL2 (License: https://docs.nvidia.com/deeplearning/sdk/nccl-sla/index.html)
 RUN \

tests/ci_build/prune_libnccl.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+set -e
+
+rm -rf tmp_nccl
+
+mkdir tmp_nccl
+pushd tmp_nccl
+
+set -x
+
+cat << EOF > test.cu
+int main(void) { return 0; }
+EOF
+
+cat << EOF > CMakeLists.txt
+cmake_minimum_required(VERSION 3.18 FATAL_ERROR)
+project(gencode_extractor CXX C)
+cmake_policy(SET CMP0104 NEW)
+set(CMAKE_CUDA_HOST_COMPILER \${CMAKE_CXX_COMPILER})
+enable_language(CUDA)
+include(../cmake/Utils.cmake)
+set(GEN_CODE "")
+format_gencode_flags("" GEN_CODE)
+add_library(test OBJECT test.cu)
+set_property(TARGET test PROPERTY CUDA_ARCHITECTURES \${CMAKE_CUDA_ARCHITECTURES})
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+EOF
+
+cmake . -GNinja
+gen_code=$(grep -o -- '--generate-code=\S*' compile_commands.json | paste -sd ' ')
+
+nvprune ${gen_code} /usr/lib64/libnccl_static.a -o ../libnccl_static.a
+
+popd
+rm -rf tmp_nccl
+
+set +x