[clang] [lld] [llvm] [LTO][LLD] Prevent invalid LTO libfunc transforms (PR #164916)

[Peter Smith via llvm-commits]

================
@@ -2701,15 +2701,30 @@ static void markBuffersAsDontNeed(Ctx &ctx, bool skipLinkedOutput) {
 template <class ELFT>
 void LinkerDriver::compileBitcodeFiles(bool skipLinkedOutput) {
   llvm::TimeTraceScope timeScope("LTO");
+  // Capture the triple before moving the bitcode into the bitcode compiler.
+  std::optional<llvm::Triple> tt;
+  if (!ctx.bitcodeFiles.empty())
+    tt = llvm::Triple(ctx.bitcodeFiles.front()->obj->getTargetTriple());
   // Compile bitcode files and replace bitcode symbols.
   lto.reset(new BitcodeCompiler(ctx));
   for (BitcodeFile *file : ctx.bitcodeFiles)
     lto->add(*file);
 
-  if (!ctx.bitcodeFiles.empty())
+  llvm::BumpPtrAllocator alloc;
+  llvm::StringSaver saver(alloc);
+  SmallVector<StringRef> bitcodeLibFuncs;
+  if (!ctx.bitcodeFiles.empty()) {
     markBuffersAsDontNeed(ctx, skipLinkedOutput);
+    for (StringRef libFunc : lto::LTO::getLibFuncSymbols(*tt, saver)) {
+      Symbol *sym = ctx.symtab->find(libFunc);
----------------
smithp35 wrote:

Could the test for sym == nullptr be combined with the find?
```
if (Symbol *sym = ctx.symtab->find(libFunc))
  if (isa<BitcodeFile>(sym->file))
        bitcodeLibFuncs.push_back(libFunc);
```

https://github.com/llvm/llvm-project/pull/164916