[Clang] -fseparate-named-sections option (#91028)

When set, the compiler will use separate unique sections for global
symbols in named special sections (e.g. symbols that are annotated with
__attribute__((section(...)))). Doing so enables linker GC to collect
unused symbols without having to use a different section per-symbol.

1 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 2a77a68..81f3864 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -733,15 +733,20 @@ calcUniqueIDUpdateFlagsAndSize(const GlobalObject *GO, StringRef SectionName,
       Ctx.isELFGenericMergeableSection(SectionName);
   // If this is the first ocurrence of this section name, treat it as the
   // generic section
-  if (!SymbolMergeable && !SeenSectionNameBefore)
-    return MCContext::GenericSectionID;
+  if (!SymbolMergeable && !SeenSectionNameBefore) {
+    if (TM.getSeparateNamedSections())
+      return NextUniqueID++;
+    else
+      return MCContext::GenericSectionID;
+  }
 
   // Symbols must be placed into sections with compatible entry sizes. Generate
   // unique sections for symbols that have not been assigned to compatible
   // sections.
   const auto PreviousID =
       Ctx.getELFUniqueIDForEntsize(SectionName, Flags, EntrySize);
-  if (PreviousID)
+  if (PreviousID && (!TM.getSeparateNamedSections() ||
+                     *PreviousID == MCContext::GenericSectionID))
     return *PreviousID;
 
   // If the user has specified the same section name as would be created