LTO: expose LTO_SYMBOL_COMDAT flag, which indicates that the definition is part of a comdat group.

[• rafael]

With this LTO_SYMBOL_DEFINITION_WEAK will not be set if the def is in a comdat.

Given that those things are orthogonal, don't you want to make this an independent flag?

[pcc]

Make COMDAT flag orthogonal to definition

[• rafael]

Lgtm

include/llvm-c/lto.h

typedef enum {
     LTO_SYMBOL_PERMISSIONS_DATA            = 0x000000C0,
     LTO_SYMBOL_PERMISSIONS_RODATA          = 0x00000080,
     LTO_SYMBOL_DEFINITION_MASK             = 0x00000700,
     LTO_SYMBOL_DEFINITION_REGULAR          = 0x00000100,
     LTO_SYMBOL_DEFINITION_TENTATIVE        = 0x00000200,
     LTO_SYMBOL_DEFINITION_WEAK             = 0x00000300,
     LTO_SYMBOL_DEFINITION_UNDEFINED        = 0x00000400,
     LTO_SYMBOL_DEFINITION_WEAKUNDEF        = 0x00000500,
+    LTO_SYMBOL_DEFINITION_COMDAT           = 0x00000600,
     LTO_SYMBOL_SCOPE_MASK                  = 0x00003800,
     LTO_SYMBOL_SCOPE_INTERNAL              = 0x00000800,
     LTO_SYMBOL_SCOPE_HIDDEN                = 0x00001000,
     LTO_SYMBOL_SCOPE_PROTECTED             = 0x00002000,
     LTO_SYMBOL_SCOPE_DEFAULT               = 0x00001800,
     LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN = 0x00002800
 } lto_symbol_attributes;
 

lib/LTO/LTOModule.cpp

if (isFunction) {
     const GlobalVariable *gv = dyn_cast<GlobalVariable>(def);
     if (gv && gv->isConstant())
       attr |= LTO_SYMBOL_PERMISSIONS_RODATA;
     else
       attr |= LTO_SYMBOL_PERMISSIONS_DATA;
   }
 
   // set definition part
-  if (def->hasWeakLinkage() || def->hasLinkOnceLinkage())
+  if (def->hasComdat())
+    attr |= LTO_SYMBOL_DEFINITION_COMDAT;
+  else if (def->hasWeakLinkage() || def->hasLinkOnceLinkage())
     attr |= LTO_SYMBOL_DEFINITION_WEAK;
   else if (def->hasCommonLinkage())
     attr |= LTO_SYMBOL_DEFINITION_TENTATIVE;
   else
     attr |= LTO_SYMBOL_DEFINITION_REGULAR;
 
   // set scope part
   if (def->hasLocalLinkage())