COFF: Sort non-discardable sections at the same time as other sections. NFC.

[pcc]

Summary

This makes the sort order a little clearer.

[ruiu]

LGTM

[hans]

Thanks!

lld/COFF/Writer.cpp

void Writer::createSymbolAndStringTable() {
   // We position the symbol table to be adjacent to the end of the last section.
   uint64_t FileOff = FileSize;
   PointerToSymbolTable = FileOff;
   FileOff += OutputSymtab.size() * sizeof(coff_symbol16);
   FileOff += 4 + Strtab.size();
   FileSize = alignTo(FileOff, SectorSize);
 }
 
-static int sectionIndex(StringRef Name) {
+static int sectionIndex(OutputSection *S) {
+  // Move DISCARDABLE (or non-memory-mapped) sections to the end of file because
+  // the loader cannot handle holes.
+  if (S->getPermissions() & IMAGE_SCN_MEM_DISCARDABLE)
+    return 101;
+
   // Try to match the section order used by link.exe. In particular, it's
   // important that .reloc comes last since it refers to RVA's of data in
   // the previous sections. .rsrc should come late because its size may
   // change by the Win32 UpdateResources() function, causing subsequent
   // sections to move (see https://crbug.com/827082).
-  return StringSwitch<int>(Name)
+  return StringSwitch<int>(S->Name)
       .Case(".text", 1)
       .Case(".bss", 2)
       .Case(".rdata", 3)
       .Case(".data", 4)
       .Case(".pdata", 5)
       .Case(".idata", 6)
       .Case(".rsrc", 99)
       .Case(".reloc", 100)
SizeOfHeaders +=
       Config->is64() ? sizeof(pe32plus_header) : sizeof(pe32_header);
   SizeOfHeaders = alignTo(SizeOfHeaders, SectorSize);
   uint64_t RVA = PageSize; // The first page is kept unmapped.
   FileSize = SizeOfHeaders;
 
   // Reorder the sections.
   std::stable_sort(OutputSections.begin(), OutputSections.end(),
                    [](OutputSection *S, OutputSection *T) {
-                     return sectionIndex(S->Name) < sectionIndex(T->Name);
+                     return sectionIndex(S) < sectionIndex(T);
                    });
 
-  // Move DISCARDABLE (or non-memory-mapped) sections to the end of file because
-  // the loader cannot handle holes.
-  std::stable_partition(
-      OutputSections.begin(), OutputSections.end(), [](OutputSection *S) {
-        return (S->getPermissions() & IMAGE_SCN_MEM_DISCARDABLE) == 0;
-      });
   for (OutputSection *Sec : OutputSections) {
     if (Sec->Name == ".reloc")
       addBaserels(Sec);
     uint64_t RawSize = 0, VirtualSize = 0;
     Sec->Header.VirtualAddress = RVA;
     for (Chunk *C : Sec->getChunks()) {
       VirtualSize = alignTo(VirtualSize, C->Alignment);
       C->setRVA(RVA + VirtualSize);