Restrict COFF to a single thread when symbol count is high (#50874)

src/aotcompile.cpp

@@ -651,6 +651,7 @@ static FunctionInfo getFunctionWeight(const Function &F)
 }
 
 struct ModuleInfo {
+ Triple triple;
  size_t globals;
  size_t funcs;
  size_t bbs;
@@ -661,6 +662,7 @@ struct ModuleInfo {
 
 ModuleInfo compute_module_info(Module &M) {
  ModuleInfo info;
+ info.triple = Triple(M.getTargetTriple());
  info.globals = 0;
  info.funcs = 0;
  info.bbs = 0;
@@ -1412,6 +1414,13 @@ static unsigned compute_image_thread_count(const ModuleInfo &info) {
  LLVM_DEBUG(dbgs() << "32-bit systems are restricted to a single thread\n");
  return 1;
 #endif
+ // COFF has limits on external symbols (even hidden) up to 65536. We reserve the last few
+ // for any of our other symbols that we insert during compilation.
+ if (info.triple.isOSBinFormatCOFF() && info.globals > 64000) {
+ LLVM_DEBUG(dbgs() << "COFF is restricted to a single thread for large images\n");
+ return 1;
+ }
+
  // This is not overridable because empty modules do occasionally appear, but they'll be very small and thus exit early to
  // known easy behavior. Plus they really don't warrant multiple threads
  if (info.weight < 1000) {