[llvm] [X86] Set SHF_X86_64_LARGE for globals with explicit well-known large section name (PR #74381)

[Reid Kleckner via llvm-commits]

================
@@ -55,17 +52,22 @@ bool TargetMachine::isLargeGlobalObject(const GlobalObject *GO) const {
     return false;
 
   // Allowing large metadata sections in the presence of an explicit section is
-  // useful, even if GCC does not allow them. However, we should not mark
-  // certain well-known prefixes as large, because it would make the whole
-  // output section large and cause the linker to move it, which is almost
-  // always undesired.
+  // useful, even if GCC does not allow them. However, we should properly mark
+  // well-known section name prefixes as small/large, because otherwise the
+  // output section may have the wrong section flags and the linker will lay it
+  // out in an unexpected way.
   StringRef Name = GV->getSection();
   auto IsPrefix = [&](StringRef Prefix) {
     StringRef S = Name;
     return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
   };
   if (IsPrefix(".bss") || IsPrefix(".data") || IsPrefix(".rodata"))
     return false;
+  if (IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata"))
+    return true;
+
+  if (getCodeModel() != CodeModel::Medium && getCodeModel() != CodeModel::Large)
+    return false;
 
   const DataLayout &DL = GV->getParent()->getDataLayout();
----------------
rnk wrote:

I think this will read better if you nest the LargeDataThreshold check in the medium / large conditional, like:
```
if (getCodeModel() == CodeModel::Medium || getCodeModel() == CodeModel::Large) {
...
  return Size == 0 || Size > LargeDataThreshold;
}
return false;
```

https://github.com/llvm/llvm-project/pull/74381