CI: Guard compile-time CPU features tests

  This guard protects against any sudden unexpected changes that may adversely
  affect the compile-time SIMD features detection which could leave the SIMD code
  inactivated. Until now we have faced two cases:

  1. Hardening the compile-time test files of Neon/ASIMD features without checking
     the sanity of the modification leading to disabling all optimizations on aarch64.
     see numpygh-21747

  2. A sudden compiler upgrades by CI side on s390x that causes conflicts with the
     installed assembler leading to disabling the whole VX/E features, which made us
     merge SIMD code without testing it. Later, it was discovered that this code
     disrupted the NumPy build.
     see numpygh-21750, numpygh-21748

.github/workflows/build_test.yml

@@ -61,6 +61,8 @@ jobs:
     strategy:
       matrix:
         python-version: ["3.9", "3.10", "3.11-dev"]
+    env:
+      EXPECT_CPU_FEATURES: "SSE SSE2 SSE3 SSSE3 SSE41 POPCNT SSE42 AVX F16C FMA3 AVX2 AVX512F AVX512CD AVX512_KNL AVX512_KNM AVX512_SKX AVX512_CLX AVX512_CNL AVX512_ICL"
     steps:
     - uses: actions/checkout@v3
       with:

.travis.yml

@@ -34,6 +34,8 @@ jobs:
        - DOWNLOAD_OPENBLAS=1
        - NPY_USE_BLAS_ILP64=1
        - ATLAS=None
+       # VSX4 still not supported by ubuntu/gcc-11
+       - EXPECT_CPU_FEATURES="VSX VSX2 VSX3"
 
     - python: "3.8"
       os: linux
@@ -46,6 +48,7 @@ jobs:
        - DOWNLOAD_OPENBLAS=1
        - NPY_USE_BLAS_ILP64=1
        - ATLAS=None
+       - EXPECT_CPU_FEATURES="VX VXE VXE2"
 
     # Wheel builders
     - python: "3.8"
@@ -54,6 +57,7 @@ jobs:
       virt: vm
       env:
         - CIBW_BUILD: cp38-manylinux_aarch64
+        - EXPECT_CPU_FEATURES: "NEON NEON_FP16 NEON_VFPV4 ASIMD ASIMDHP ASIMDDP ASIMDFHM"
       install: python3 -m pip install cibuildwheel==2.4.0
       script: |
         cibuildwheel --output-dir wheelhouse

tools/travis-test.sh

@@ -103,6 +103,42 @@ run_test()
     "import os; import numpy; print(os.path.dirname(numpy.__file__))")
   export PYTHONWARNINGS=default
 
+  # This guard protects against any sudden unexpected changes that may adversely
+  # affect the compile-time SIMD features detection which could leave the SIMD code
+  # inactivated. Until now we have faced two cases:
+  #
+  # 1. Hardening the compile-time test files of Neon/ASIMD features without checking
+  # the sanity of the modification leading to disabling all optimizations on aarch64.
+  # see gh-21747
+  #
+  # 2. A sudden compiler upgrades by CI side on s390x that causes conflicts with the
+  # installed assembler leading to disabling the whole VX/E features, which made us
+  # merge SIMD code without testing it. Later, it was discovered that this code
+  # disrupted the NumPy build.
+  # see gh-21750, gh-21748
+  if [ -n "$EXPECT_CPU_FEATURES" ]; then
+    as_expected=$($PYTHON << EOF
+from numpy.core._multiarray_umath import (__cpu_baseline__, __cpu_dispatch__)
+features = __cpu_baseline__ + __cpu_dispatch__
+expected = '$EXPECT_CPU_FEATURES'.upper().split()
+diff = set(expected).difference(set(features))
+if diff:
+    print("Unexpected compile-time CPU features detection!\n"
+          f"The current build is missing the support of CPU features '{diff}':\n"
+          "This error is triggered because of one of the following reasons:\n\n"
+          f"1. The compiler for somehow no longer supports any of these CPU features {diff}\n"
+          f"Note that the current build reports the support of the following features:\n{features}\n\n"
+          "2. Your code messed up the testing process! please check the build log and trace\n"
+          "compile-time feature tests and make sure that your patch has nothing to do with the tests failures."
+          )
+EOF
+)
+    if [ -n "$as_expected" ]; then
+      echo "$as_expected"
+      exit 1
+    fi
+  fi
+
   if [ -n "$CHECK_BLAS" ]; then
     $PYTHON ../tools/openblas_support.py --check_version
   fi