Fix a few issues with comdat handling on COFF.

* Section association cannot use just the section name as many
sections can have the same name. With this patch, the comdat symbol in
an assoc section is interpreted to mean a symbol in the associated
section and the mapping is discovered from it.

* Comdat symbols were not being set correctly. Instead we were getting
whatever was output first for that section.

A consequence is that associative sections now must use .section to
set the association. Using .linkonce would not work since it is not
possible to change a sections comdat symbol (it is used to decide if
we should create a new section or reuse an existing one).

This includes r210298, which was reverted because it was asserting
on an associated section having the same comdat as the associated
section.

llvm-svn: 210367

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/lib/MC/MCSectionCOFF.cpp b/llvm/lib/MC/MCSectionCOFF.cpp
index 335b8cd..fc2bd36 100644
--- a/llvm/lib/MC/MCSectionCOFF.cpp
+++ b/llvm/lib/MC/MCSectionCOFF.cpp
@@ -30,14 +30,9 @@ bool MCSectionCOFF::ShouldOmitSectionDirective(StringRef Name,
   return false;
 }
 
-void MCSectionCOFF::setSelection(int Selection,
-                                 const MCSectionCOFF *Assoc) const {
+void MCSectionCOFF::setSelection(int Selection) const {
   assert(Selection != 0 && "invalid COMDAT selection type");
-  assert((Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) ==
-         (Assoc != nullptr) &&
-    "associative COMDAT section must have an associated section");
   this->Selection = Selection;
-  this->Assoc = Assoc;
   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
 }
 
@@ -82,7 +77,7 @@ void MCSectionCOFF::PrintSwitchToSection(const MCAsmInfo &MAI,
         OS << "same_contents,";
         break;
       case COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE:
-        OS << "associative " << Assoc->getSectionName() << ",";
+        OS << "associative,";
         break;
       case COFF::IMAGE_COMDAT_SELECT_LARGEST:
         OS << "largest,";