[llvm] [X86] Don't respect large data threshold for globals with an explicit section (PR #78348)

[Fangrui Song via llvm-commits]

================
@@ -58,31 +58,31 @@ bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
   if (GV->isThreadLocal())
     return false;
 
-  // 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();
-  if (!Name.empty()) {
-    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;
-  }
-
   // For x86-64, we treat an explicit GlobalVariable small code model to mean
   // that the global should be placed in a small section, and ditto for large.
-  // Well-known section names above take precedence for correctness.
   if (auto CM = GV->getCodeModel()) {
     if (*CM == CodeModel::Small)
       return false;
     if (*CM == CodeModel::Large)
       return true;
   }
 
+  // Treat all globals in explicit sections as small, except for the standard
+  // large sections of .lbss, .ldata, .lrodata. This reduces the risk of linking
+  // together small and large sections, resulting in small references to large
+  // data sections. The code model attribute overrides this above.
+  if (GV->hasSection()) {
+    StringRef Name = GV->getSection();
+    auto IsPrefix = [&](StringRef Prefix) {
+      StringRef S = Name;
+      return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
+    };
+    if (IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata"))
----------------
MaskRay wrote:

`return IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata")`

https://github.com/llvm/llvm-project/pull/78348