Fix build with C++11 (pytorch#223)

Summary:
Pull Request resolved: pytorch#223

^

(Note: this ignores all push blocking failures!)

Reviewed By: dskhudia

Differential Revision: D19131462

fbshipit-source-id: 6bf8305099fb1a694612aa70ee0ee8ac65ca744d

src/Utils.cc

@@ -242,18 +242,29 @@ bool fbgemmEnvAvx512_256Enabled() {
   return val == "true" || val == "1";
 }
 
-std::unordered_map<inst_set_t, std::unordered_set<inst_set_t>> isaSupportMap = {
-    {inst_set_t::anyarch, {inst_set_t::anyarch}},
-    {inst_set_t::avx2, {inst_set_t::avx2, inst_set_t::anyarch}},
-    {inst_set_t::avx512,
-      {inst_set_t::avx512, inst_set_t::avx512_ymm, inst_set_t::avx2}},
-    {inst_set_t::avx512_ymm,
-      {inst_set_t::avx512, inst_set_t::avx512_ymm, inst_set_t::avx2}},
-    {inst_set_t::avx512_vnni,
+// This is require for build by older compilers GCC 5.4 and C++11
+struct inst_set_t_hash {
+  std::size_t operator()(inst_set_t t) const {
+    return static_cast<std::size_t>(t);
+  }
+};
+
+std::unordered_map<
+    inst_set_t,
+    std::unordered_set<inst_set_t, inst_set_t_hash>,
+    inst_set_t_hash>
+    isaSupportMap = {
+        {inst_set_t::anyarch, {inst_set_t::anyarch}},
+        {inst_set_t::avx2, {inst_set_t::avx2, inst_set_t::anyarch}},
+        {inst_set_t::avx512,
+         {inst_set_t::avx512, inst_set_t::avx512_ymm, inst_set_t::avx2}},
+        {inst_set_t::avx512_ymm,
+         {inst_set_t::avx512, inst_set_t::avx512_ymm, inst_set_t::avx2}},
         {inst_set_t::avx512_vnni,
-        inst_set_t::avx512,
-        inst_set_t::avx512_ymm,
-        inst_set_t::avx2}},
+         {inst_set_t::avx512_vnni,
+          inst_set_t::avx512,
+          inst_set_t::avx512_ymm,
+          inst_set_t::avx2}},
 };
 
 } // namespace
@@ -320,8 +331,9 @@ inst_set_t fbgemmInstructionSet() {
     return detected_isa;
   }
   const auto supported_isa = isaSupportMap.find(detected_isa);
-  assert(supported_isa != isaSupportMap.end()
-      && "Detected ISA can't be located in Supported ISA map");
+  assert(
+      supported_isa != isaSupportMap.end() &&
+      "Detected ISA can't be located in Supported ISA map");
   if (supported_isa == isaSupportMap.end()) {
     return detected_isa;
   }