[lld] [lld] check cache before real_path in loadDylib (PR #140791)

[Daniel Rodríguez Troitiño via llvm-commits]

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@@ -229,19 +229,31 @@ static DenseMap<CachedHashStringRef, DylibFile *> loadedDylibs;
 
 DylibFile *macho::loadDylib(MemoryBufferRef mbref, DylibFile *umbrella,
                             bool isBundleLoader, bool explicitlyLinked) {
-  // Frameworks can be found from different symlink paths, so resolve
-  // symlinks before looking up in the dylib cache.
-  SmallString<128> realPath;
-  std::error_code err = fs::real_path(mbref.getBufferIdentifier(), realPath);
-  CachedHashStringRef path(!err ? uniqueSaver().save(StringRef(realPath))
-                                : mbref.getBufferIdentifier());
+  CachedHashStringRef path(mbref.getBufferIdentifier());
   DylibFile *&file = loadedDylibs[path];
   if (file) {
     if (explicitlyLinked)
       file->setExplicitlyLinked();
     return file;
   }
 
+  // Frameworks can be found from different symlink paths, so resolve
+  // symlinks and look up in the dylib cache.
+  DylibFile *&realfile = file;
+  SmallString<128> realPath;
+  std::error_code err = fs::real_path(mbref.getBufferIdentifier(), realPath);
+  if (!err) {
+    CachedHashStringRef resolvedPath(uniqueSaver().save(StringRef(realPath)));
+    realfile = loadedDylibs[resolvedPath];
+    if (realfile) {
+      if (explicitlyLinked)
+        realfile->setExplicitlyLinked();
+
+      file = realfile;
----------------
drodriguez wrote:

We should not have added that line then.

I found this about references to `unordered_map` being invalidated: https://eel.is/c++draft/unord.req#general-9 (emphasis mine)

> Rehashing invalidates iterators, changes ordering between elements, and changes which buckets elements appear in, but **does not invalidate pointers or references** to elements

I am not sure if `llvm::DenseMap` follows all the rules of `std::unordered_map`, but that little bit might be something they forgot to keep compatible.


https://github.com/llvm/llvm-project/pull/140791