ELF: Enable address-significance tables during LTO.

[pcc]

Summary

This allows safe ICF to work when linking with LTO.

[pcc]

Ping

[ruiu]

LGTM

ELF/LTO.cpp

static std::string getThinLTOOutputFile(StringRef ModulePath) {
   return lto::getThinLTOOutputFile(ModulePath,
                                    Config->ThinLTOPrefixReplace.first,
                                    Config->ThinLTOPrefixReplace.second);
 }
 
 static lto::Config createConfig() {
   lto::Config C;
 
-  // LLD supports the new relocations.
+  // LLD supports the new relocations and address-significance tables.
   C.Options = InitTargetOptionsFromCodeGenFlags();
   C.Options.RelaxELFRelocations = true;
+  C.Options.EmitAddrsig = true;
 
   // Always emit a section per function/datum with LTO.
   C.Options.FunctionSections = true;
   C.Options.DataSections = true;
 
   if (Config->Relocatable)
     C.RelocModel = None;
   else if (Config->Pic)

test/ELF/lto/relocatable.ll

 ; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 0
 ; CHECK-NEXT:     Binding: Local
 ; CHECK-NEXT:     Type: Section
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: .text.foo
 ; CHECK-NEXT:   }
 ; CHECK-NEXT:   Symbol {
+; CHECK-NEXT:     Name:
+; CHECK-NEXT:     Value: 0x0
+; CHECK-NEXT:     Size: 0
+; CHECK-NEXT:     Binding: Local
+; CHECK-NEXT:     Type: Section
+; CHECK-NEXT:     Other: 0
+; CHECK-NEXT:     Section: .llvm_addrsig
+; CHECK-NEXT:   }
+; CHECK-NEXT:   Symbol {
 ; CHECK-NEXT:     Name: foo
 ; CHECK-NEXT:     Value: 0x0
 ; CHECK-NEXT:     Size: 1
 ; CHECK-NEXT:     Binding: Global
 ; CHECK-NEXT:     Type: Function
 ; CHECK-NEXT:     Other: 0
 ; CHECK-NEXT:     Section: .text.foo
 ; CHECK-NEXT:   }