Fix -Wmaybe-uninitialized errors

[stefwalter]

These come up when building FBGEMM as part of Pytorch or other stacks.

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[stefwalter]

Examples of the build problems:

/data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc: In function ‘void fbgemm::depthwise_3d_same_pad_(const conv_param_t<3>&, int32_t, const uint8_t*, const int32_t*, const PackedDepthWiseConvMatrix&, const float*, int32_t, uint8_t*, const int32_t*, const BIAS_TYPE*, const float*, int, int) [with bool FUSE_RELU = true; bool HAS_BIAS = true; QuantizationGranularity Q_GRAN = fbgemm::QuantizationGranularity::GROUP; BIAS_TYPE = int]’:
/data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc:657:46: note: ‘kernel’ was declared here
  657 |         GenI8Depthwise::jit_kernel_signature kernel;
      |                                              ^~~~~~
In function ‘void fbgemm::depthwise_3d_kernel_(int, int, int, int, int, int, int, int, std::array<int, 3>, int, int, int, int32_t, const uint8_t*, const int32_t*, const int8_t*, const float*, int32_t, int32_t*, uint8_t*, int32_t*, const int32_t*, const BIAS_TYPE*, const float*, void (**)(const uint8_t*, const int8_t*, int32_t*, int32_t*, int, int, int, const int*, int)) [with bool FUSE_RELU = true; bool HAS_BIAS = true; bool A_SYMMETRIC = true; bool B_SYMMETRIC = false; QuantizationGranularity Q_GRAN = fbgemm::QuantizationGranularity::GROUP; BIAS_TYPE = int]’,
    inlined from ‘void fbgemm::depthwise_3d_same_pad_(const conv_param_t<3>&, int32_t, const uint8_t*, const int32_t*, const PackedDepthWiseConvMatrix&, const float*, int32_t, int32_t*, uint8_t*, const int32_t*, const BIAS_TYPE*, const float*, int, int) [with bool FUSE_RELU = true; bool HAS_BIAS = true; bool A_SYMMETRIC = true; bool B_SYMMETRIC = false; QuantizationGranularity Q_GRAN = fbgemm::QuantizationGranularity::GROUP; BIAS_TYPE = int]’ at /data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc:293:22,
    inlined from ‘void fbgemm::depthwise_3d_same_pad_(const conv_param_t<3>&, int32_t, const uint8_t*, const int32_t*, const PackedDepthWiseConvMatrix&, const float*, int32_t, uint8_t*, const int32_t*, const BIAS_TYPE*, const float*, int, int) [with bool FUSE_RELU = true; bool HAS_BIAS = true; QuantizationGranularity Q_GRAN = fbgemm::QuantizationGranularity::GROUP; BIAS_TYPE = int]’ at /data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc:834:18:
/data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc:86:9: error: ‘kernel’ may be used uninitialized [-Werror=maybe-uninitialized]
   86 |   kernel(
      |   ~~~~~~^
   87 |       A + ((t_in * H + h_in) * W + w_in) * IC,
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   88 |       Bp,
      |       ~~~
   89 |       C_int32,
      |       ~~~~~~~~
   90 |       B_SYMMETRIC ? nullptr : row_offsets,
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   91 |       H,
      |       ~~ 
   92 |       W,
      |       ~~ 
   93 |       IC,
      |       ~~~
   94 |       internal::avx2_ps_or_epi32_combined_mask,
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   95 |       A_zero_point);
      |       ~~~~~~~~~~~~~
/data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc: In function ‘void fbgemm::depthwise_3d_same_pad_(const conv_param_t<3>&, int32_t, const uint8_t*, const int32_t*, const PackedDepthWiseConvMatrix&, const float*, int32_t, uint8_t*, const int32_t*, const BIAS_TYPE*, const float*, int, int) [with bool FUSE_RELU = true; bool HAS_BIAS = true; QuantizationGranularity Q_GRAN = fbgemm::QuantizationGranularity::GROUP; BIAS_TYPE = int]’:
/data/src/FBGEMM/src/FbgemmI8Depthwise3DAvx2.cc:267:46: note: ‘kernel’ was declared here
  267 |         GenI8Depthwise::jit_kernel_signature kernel;
      |                                              ^~~~~~

And another:

...
  /usr/bin/c++ -DFBGEMM_STATIC -I/data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/cpuinfo/include -I/data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/third_party/asmjit/src -I/data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/include -I/data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm -I/data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/cmake/../third_party/benchmark/include -isystem /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/cmake/../third_party/googletest/googlemock/include -isystem /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/cmake/../third_party/googletest/googletest/include -isystem /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/protobuf/src -isystem /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/gemmlowp -isystem /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/neon2sse -isystem /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/XNNPACK/include -D_GLIBCXX_USE_CXX11_ABI=1 -fvisibility-inlines-hidden -DUSE_PTHREADPOOL -fopenmp -Wall -Wextra -Werror -Wno-deprecated-declarations -Wimplicit-fallthrough -O3 -DNDEBUG -std=c++17 -fPIC -fvisibility=hidden -m64 -mavx2 -mfma -mavx512f -mavx512bw -mavx512dq -mavx512vl -MD -MT third_party/fbgemm/CMakeFiles/fbgemm_avx512.dir/src/UtilsAvx512.cc.o -MF third_party/fbgemm/CMakeFiles/fbgemm_avx512.dir/src/UtilsAvx512.cc.o.d -o third_party/fbgemm/CMakeFiles/fbgemm_avx512.dir/src/UtilsAvx512.cc.o -c /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/src/UtilsAvx512.cc
  In function ‘void fbgemm::internal::transpose_contiguous_16x2_block(const float*, float*, int64_t, int)’,
      inlined from ‘void fbgemm::internal::transpose_avx512_contiguous_thin(int64_t, int64_t, const T*, int64_t, T*, int64_t) [with T = float]’ at /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/src/UtilsAvx512.cc:1827:38:
  /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/src/UtilsAvx512.cc:970:35: error: ‘r’ may be used uninitialized [-Werror=maybe-uninitialized]
    970 |   d[0] = _mm512_permutex2var_epi32(r[0], index1, r[1]);
        |          ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
  /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/src/UtilsAvx512.cc: In function ‘void fbgemm::internal::transpose_avx512_contiguous_thin(int64_t, int64_t, const T*, int64_t, T*, int64_t) [with T = float]’:
  /data/src/rebuilding-the-wheel/work-dir/pytorch-v2.2.2/pytorch-v2.2.2/third_party/fbgemm/src/UtilsAvx512.cc:922:11: note: ‘r’ declared here
    922 |   __m512i r[2], d[2];
        |           ^
  cc1plus: all warnings being treated as errors

[markmc]

@stefwalter seems this is a gcc issue, see #1666

This uninitialized variable issue is being addressed with https://github.com/pytorch/FBGEMM/pull/1697. However, this alone will not fix the build because there a known regression in GCC 12 (see here).

[stefwalter]

@stefwalter seems this is a gcc issue, see #1666

This uninitialized variable issue is being addressed with #1697. However, this alone will not fix the build because there a known regression in GCC 12 (see here).

Hmmm, yup seems like that could well be the case. Here's what I'm building with (on Fedora 40):

stef@falcon:~/src/linux$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/14/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,m2,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --enable-libstdcxx-backtrace --with-libstdcxx-zoneinfo=/usr/share/zoneinfo --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-14.0.1-20240411/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none,amdgcn-amdhsa --enable-offload-defaulted --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux --with-build-config=bootstrap-lto --enable-link-serialization=1
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.1 20240411 (Red Hat 14.0.1-0) (GCC)