Remove fbgemm autovec (pytorch#4123)

Summary:

DO NOT LAND

Testing PyTorch CI without fbgemm autovec

Differential Revision: D74747522

Author: gchalump

CMakeLists.txt

@@ -422,3 +422,7 @@ endif()
 if(FBGEMM_BUILD_FBGEMM_GPU)
   add_subdirectory(fbgemm_gpu)
 endif()
+
+if(HAVE_GNU_F2H_IEEE)
+    add_definitions(-DHAVE_GNU_F2H_IEEE)
+endif()

cmake/modules/FindGnuH2fIeee.cmake

@@ -0,0 +1,21 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+
+################################################################################
+# Finds and sets GNU_FH2_IEEE compilation flags
+################################################################################
+
+INCLUDE(CheckCXXSourceCompiles)
+
+CHECK_CXX_SOURCE_COMPILES("
+    #include <arm_neon.h>
+    int main() {
+        float f = 1.0f;
+        uint16_t h = __gnu_f2h_ieee(f);
+        return 0;
+    }
+" HAVE_GNU_F2H_IEEE)

fbgemm_gpu/cmake/Fbgemm.cmake

@@ -10,7 +10,6 @@
 
 set(fbgemm_sources_normal
   "${FBGEMM}/src/EmbeddingSpMDM.cc"
-  "${FBGEMM}/src/EmbeddingSpMDMAutovec.cc"
   "${FBGEMM}/src/EmbeddingSpMDMNBit.cc"
   "${FBGEMM}/src/QuantUtils.cc"
   "${FBGEMM}/src/RefImplementations.cc"

include/fbgemm/FloatConversion.h

@@ -287,7 +287,7 @@ inline float cpu_half2float_ref(const float16 h) {
 // Same as the previous function, but use the built-in fp16 to fp32
 // conversion provided by the compiler
 inline float cpu_half2float(const float16 h) {
-#ifdef HAS_NATIVE_FP16_TYPE
+#if defined(HAS_NATIVE_FP16_TYPE) && defined(HAVE_GNU_F2H_IEEE)
   __fp16 h_fp16;
   std::memcpy(&h_fp16, &h, sizeof(__fp16));
   return h_fp16;
@@ -297,7 +297,7 @@ inline float cpu_half2float(const float16 h) {
 }
 
 inline float16 cpu_float2half(const float f) {
-#ifdef HAS_NATIVE_FP16_TYPE
+#if defined(HAS_NATIVE_FP16_TYPE) && defined(HAVE_GNU_F2H_IEEE)
   __fp16 h = f;
   float16 res;
   std::memcpy(&res, &h, sizeof(__fp16));