clang+lld: Improve clang+ld.darwinnew.lld interaction, pass -demangle

This patch:
- adds an ld64.lld.darwinnew symlink for lld, to go with f2710d4b576,
  so that `clang -fuse-ld=lld.darwinnew` can be used to test new
  Mach-O lld while it's in bring-up. (The expectation is that we'll
  remove this again once new Mach-O lld is the defauld and only Mach-O
  lld.)
- lets the clang driver know if the linker is lld (currently
  only triggered if `-fuse-ld=lld` or `-fuse-ld=lld.darwinnew` is
  passed). Currently only used for the next point, but could be used
  to implement other features that need close coordination between
  compiler and linker, e.g. having a diag for calling `clang++` instead
  of `clang` when link errors are caused by a missing C++ stdlib.
- lets the clang driver pass `-demangle` to Mach-O lld (both old and
  new), in addition to ld64
- implements -demangle for new Mach-O lld
- changes demangleItanium() to accept _Z, __Z, ___Z, ____Z prefixes
  (and updates one test added in D68014). Mach-O has an extra
  underscore for symbols, and the three (or, on Mach-O, four)
  underscores are used for block names.

Differential Revision: https://reviews.llvm.org/D91884

5 files changed, 6 insertions, 6 deletions

diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
index 633dbb0184fc..82c017063d44 100644
--- a/lld/MachO/Config.h
+++ b/lld/MachO/Config.h
@@ -43,6 +43,7 @@ struct Configuration {
   uint32_t headerPad;
   llvm::StringRef installName;
   llvm::StringRef outputFile;
+  bool demangle = false;
   llvm::MachO::Architecture arch;
   PlatformInfo platform;
   llvm::MachO::HeaderFileType outputType;
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index 3b1daadf9f0a..0f5da218e80d 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -584,6 +584,7 @@ bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
   config->runtimePaths = args::getStrings(args, OPT_rpath);
   config->allLoad = args.hasArg(OPT_all_load);
   config->forceLoadObjC = args.hasArg(OPT_ObjC);
+  config->demangle = args.hasArg(OPT_demangle);
 
   if (const opt::Arg *arg = args.getLastArg(OPT_static, OPT_dynamic))
     config->staticLink = (arg->getOption().getID() == OPT_static);
diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
index 3695bd1e2868..4aa999826fb6 100644
--- a/lld/MachO/Options.td
+++ b/lld/MachO/Options.td
@@ -1107,9 +1107,7 @@ def debug_snapshot : Flag<["-"], "debug_snapshot">,
      Flags<[HelpHidden]>,
      Group<grp_undocumented>;
 def demangle : Flag<["-"], "demangle">,
-     HelpText<"This option is undocumented in ld64">,
-     Flags<[HelpHidden]>,
-     Group<grp_undocumented>;
+     HelpText<"Demangle symbol names in diagnostics">;
 def dyld_env : Flag<["-"], "dyld_env">,
      HelpText<"This option is undocumented in ld64">,
      Flags<[HelpHidden]>,
diff --git a/lld/MachO/Symbols.cpp b/lld/MachO/Symbols.cpp
index 75c699781a61..87bbab00901f 100644
--- a/lld/MachO/Symbols.cpp
+++ b/lld/MachO/Symbols.cpp
@@ -33,8 +33,8 @@ void LazySymbol::fetchArchiveMember() { file->fetch(sym); }
 
 // Returns a symbol for an error message.
 std::string lld::toString(const Symbol &sym) {
-  if (Optional<std::string> s = demangleItanium(sym.getName()))
-    return *s;
+  if (config->demangle)
+    return demangleItanium(sym.getName());
   return std::string(sym.getName());
 }
 
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
index c5239469ff2d..fa42c1c7e61c 100644
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -379,7 +379,7 @@ void Writer::scanRelocations() {
     for (Reloc &r : isec->relocs) {
       if (auto *s = r.referent.dyn_cast<lld::macho::Symbol *>()) {
         if (isa<Undefined>(s))
-          error("undefined symbol " + s->getName() + ", referenced from " +
+          error("undefined symbol " + toString(*s) + ", referenced from " +
                 sys::path::filename(isec->file->getName()));
         else
           target->prepareSymbolRelocation(s, isec, r);