[XCOFF][AIX] Put undefined symbol name into StringTable when neccessary

[jasonliu]

Summary

When we have a long name for the undefined symbol, we would hit this assertion:
Assertion failed: I != StringIndexMap.end() && "String is not in table!"
This patch addresses that.

[DiggerLin]

LGTM

[daltenty]

LGTM

llvm/lib/MC/XCOFFObjectWriter.cpp

void XCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
   for (const MCSymbol &S : Asm.symbols()) {
     // Nothing to do for temporary symbols.
     if (S.isTemporary())
       continue;
 
     const MCSymbolXCOFF *XSym = cast<MCSymbolXCOFF>(&S);
     const MCSectionXCOFF *ContainingCsect = XSym->getContainingCsect();
 
-    // Handle undefined symbol.
     if (ContainingCsect->getCSectType() == XCOFF::XTY_ER) {
+      // Handle undefined symbol.
       UndefinedCsects.emplace_back(ContainingCsect);
       SectionMap[ContainingCsect] = &UndefinedCsects.back();
-      continue;
-    }
-
+    } else {
       // If the symbol is the csect itself, we don't need to put the symbol
       // into csect's Syms.
       if (XSym == ContainingCsect->getQualNameSymbol())
         continue;
 
       assert(SectionMap.find(ContainingCsect) != SectionMap.end() &&
              "Expected containing csect to exist in map");
-
       // Lookup the containing csect and add the symbol to it.
       SectionMap[ContainingCsect]->Syms.emplace_back(XSym);
+    }
 
     // If the name does not fit in the storage provided in the symbol table
     // entry, add it to the string table.
     if (nameShouldBeInStringTable(XSym->getName()))
       Strings.add(XSym->getName());
-    }
 
   Strings.finalize();
   assignAddressesAndIndices(Layout);
 }
 
 void XCOFFObjectWriter::recordRelocation(MCAssembler &Asm,
                                          const MCAsmLayout &Layout,
                                          const MCFragment *Fragment,

llvm/test/CodeGen/PowerPC/aix-undef-func-call.ll

 ; RUN: llc -mtriple powerpc-ibm-aix-xcoff -filetype=obj -o %t.o < %s
 ; RUN: llvm-readobj  --symbols %t.o | FileCheck %s
 
 define void @bar() {
 entry:
   call void bitcast (void (...)* @foo to void ()*)()
+  call void bitcast (void (...)* @long_undef_name to void ()*)()
   ret void
 }
 
 declare void @foo(...)
+declare void @long_undef_name(...)
 
 ;CHECK: Symbol {
 ;CHECK:   Name: .foo
 ;CHECK-NEXT:   Value (RelocatableAddress): 0x0
 ;CHECK-NEXT:   Section: N_UNDEF
 ;CHECK-NEXT:   Type: 0x0
 ;CHECK-NEXT:   StorageClass: C_EXT (0x2)
 ;CHECK-NEXT:   NumberOfAuxEntries: 1
 ;CHECK-NEXT:   CSECT Auxiliary Entry {
 ;CHECK:          SectionLen: 0
 ;CHECK-NEXT:     ParameterHashIndex: 0x0
 ;CHECK-NEXT:     TypeChkSectNum: 0x0
 ;CHECK-NEXT:     SymbolAlignmentLog2: 0
 ;CHECK-NEXT:     SymbolType: XTY_ER (0x0)
 ;CHECK-NEXT:     StorageMappingClass: XMC_PR (0x0)
 ;CHECK-NEXT:     StabInfoIndex: 0x0
 ;CHECK-NEXT:     StabSectNum: 0x0
 ;CHECK-NEXT:   }
 ;CHECK-NEXT: }
+;CHECK: Symbol {
+;CHECK:   Name: .long_undef_name
+;CHECK-NEXT:   Value (RelocatableAddress): 0x0
+;CHECK-NEXT:   Section: N_UNDEF
+;CHECK-NEXT:   Type: 0x0
+;CHECK-NEXT:   StorageClass: C_EXT (0x2)
+;CHECK-NEXT:   NumberOfAuxEntries: 1
+;CHECK-NEXT:   CSECT Auxiliary Entry {
+;CHECK:          SectionLen: 0
+;CHECK-NEXT:     ParameterHashIndex: 0x0
+;CHECK-NEXT:     TypeChkSectNum: 0x0
+;CHECK-NEXT:     SymbolAlignmentLog2: 0
+;CHECK-NEXT:     SymbolType: XTY_ER (0x0)
+;CHECK-NEXT:     StorageMappingClass: XMC_PR (0x0)
+;CHECK-NEXT:     StabInfoIndex: 0x0
+;CHECK-NEXT:     StabSectNum: 0x0
+;CHECK-NEXT:   }
+;CHECK-NEXT: }