[JITLink] Add anonymous symbols in LinkGraph for unnamed temporary symbols

[StephenFan]

Summary

In RISCV, temporary symbols will be used to generate dwarf, eh_frame sections..., and will be placed in object code's symbol table. However, LLVM does not use names on these temporary symbols. This patch add anonymous symbols in LinkGraph for these temporary symbols.

[StephenFan]

Amend comments

[StephenFan]

Fix typos

[StephenFan]

Add a testcase

[lhames]

LGTM. Thanks Stefan!

[StephenFan]

rebase

[StephenFan]

Reverted due to miss # REQUIRES: asserts in test file

[lhames]

This was reapplied with fixes in 0283b07746e87.

llvm/lib/ExecutionEngine/JITLink/ELFLinkGraphBuilder.h

if (Sym.isDefined() &&
           dbgs() << "      " << SymIndex
                  << ": Creating defined graph symbol for ELF symbol \"" << *Name
                  << "\"\n";
         });
 
         if (Sym.getType() == ELF::STT_SECTION)
           *Name = GraphSec->getName();
 
+        // In RISCV, temporary symbols (Used to generate dwarf, eh_frame
+        // sections...) will appear in object code's symbol table, and LLVM does
+        // not use names on these temporary symbols (RISCV gnu toolchain uses
+        // names on these temporary symbols). If the symbol is unnamed, add
+        // anonymous symbols.
         auto &GSym =
-            G->addDefinedSymbol(*B, Sym.getValue(), *Name, Sym.st_size, L, S,
-                                Sym.getType() == ELF::STT_FUNC, false);
+            Name->empty()
+                ? G->addAnonymousSymbol(*B, Sym.getValue(), Sym.st_size,
+                                        Sym.getType() == ELF::STT_FUNC, false)
+                : G->addDefinedSymbol(*B, Sym.getValue(), *Name, Sym.st_size, L,
+                                      S, Sym.getType() == ELF::STT_FUNC, false);
         setGraphSymbol(SymIndex, GSym);
       }
     } else if (Sym.isUndefined() && Sym.isExternal()) {
       LLVM_DEBUG({
         dbgs() << "      " << SymIndex
                << ": Creating external graph symbol for ELF symbol \"" << *Name
                << "\"\n";
       });