Create unique, but identically-named ELF sections for explicitly-sectioned functions and globals when using -function-sections and -data-sections.

This allows functions and globals to to be reordered later in the linking phase
(using the -symbol-ordering-file) even though reordering will be limited to
the scope of the explicit section.

Patch by Rahman Lavaee!

Differential Revision: https://reviews.llvm.org/D65478

llvm-svn: 367501

1 files changed, 17 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index ac7c4c5..7a93a26 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -586,15 +586,30 @@ MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
     Flags |= ELF::SHF_GROUP;
   }
 
+  bool EmitUniqueSection = false;
+
+  // If we have -ffunction-sections or -fdata-sections then we should emit the
+  // global value to a uniqued section of the same name.
+  if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
+    if (Kind.isText())
+      EmitUniqueSection = TM.getFunctionSections();
+    else
+      EmitUniqueSection = TM.getDataSections();
+  }
+  EmitUniqueSection |= GO->hasComdat();
+
   // A section can have at most one associated section. Put each global with
   // MD_associated in a unique section.
-  unsigned UniqueID = MCContext::GenericSectionID;
   const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
   if (AssociatedSymbol) {
-    UniqueID = NextUniqueID++;
+    EmitUniqueSection = true;
     Flags |= ELF::SHF_LINK_ORDER;
   }
 
+  unsigned UniqueID = MCContext::GenericSectionID;
+  if (EmitUniqueSection)
+    UniqueID = NextUniqueID++;
+
   MCSectionELF *Section = getContext().getELFSection(
       SectionName, getELFSectionType(SectionName, Kind), Flags,
       getEntrySizeForKind(Kind), Group, UniqueID, AssociatedSymbol);