Revert "[lld-macho] Initial support for common symbols"

This reverts commit 63ace77962543f961f1d566dd1243b1fb37129ef.

Breaks LLDB Arm build:
http://lab.llvm.org:8011/builders/lldb-arm-ubuntu/builds/4409

6 files changed, 5 insertions, 91 deletions

diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index e95a7350921f..5e1a498f759f 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -436,31 +436,6 @@ static bool markSubLibrary(StringRef searchName) {
   return false;
 }
 
-// Replaces common symbols with defined symbols residing in __common sections.
-// This function must be called after all symbol names are resolved (i.e. after
-// all InputFiles have been loaded.) As a result, later operations won't see
-// any CommonSymbols.
-static void replaceCommonSymbols() {
-  for (macho::Symbol *sym : symtab->getSymbols()) {
-    auto *common = dyn_cast<CommonSymbol>(sym);
-    if (common == nullptr)
-      continue;
-
-    auto *isec = make<InputSection>();
-    isec->file = common->file;
-    isec->name = section_names::common;
-    isec->segname = segment_names::data;
-    isec->align = common->align;
-    isec->data = {nullptr, common->size};
-    isec->flags = S_ZEROFILL;
-    inputSections.push_back(isec);
-
-    replaceSymbol<Defined>(sym, sym->getName(), isec, /*value=*/0,
-                           /*isWeakDef=*/false,
-                           /*isExternal=*/true);
-  }
-}
-
 static inline char toLowerDash(char x) {
   if (x >= 'A' && x <= 'Z')
     return x - 'A' + 'a';
@@ -664,8 +639,6 @@ bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
       error("-sub_library " + searchName + " does not match a supplied dylib");
   }
 
-  replaceCommonSymbols();
-
   StringRef orderFile = args.getLastArgValue(OPT_order_file);
   if (!orderFile.empty())
     parseOrderFile(orderFile);
diff --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
index ad2d6a25849a..14eb1c431005 100644
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -243,12 +243,10 @@ void InputFile::parseSymbols(ArrayRef<structs::nlist_64> nList,
   for (size_t i = 0, n = nList.size(); i < n; ++i) {
     const structs::nlist_64 &sym = nList[i];
 
-    if ((sym.n_type & N_TYPE) == N_UNDF) {
+    // Undefined symbol
+    if (!sym.n_sect) {
       StringRef name = strtab + sym.n_strx;
-      symbols[i] = sym.n_value == 0
-                       ? symtab->addUndefined(name)
-                       : symtab->addCommon(name, this, sym.n_value,
-                                           1 << GET_COMM_ALIGN(sym.n_desc));
+      symbols[i] = symtab->addUndefined(name);
       continue;
     }
 
diff --git a/lld/MachO/SymbolTable.cpp b/lld/MachO/SymbolTable.cpp
index 6719981b5dff..cfb35718e7ec 100644
--- a/lld/MachO/SymbolTable.cpp
+++ b/lld/MachO/SymbolTable.cpp
@@ -74,26 +74,6 @@ Symbol *SymbolTable::addUndefined(StringRef name) {
   return s;
 }
 
-Symbol *SymbolTable::addCommon(StringRef name, InputFile *file, uint64_t size,
-                               uint32_t align) {
-  Symbol *s;
-  bool wasInserted;
-  std::tie(s, wasInserted) = insert(name);
-
-  if (!wasInserted) {
-    if (auto *common = dyn_cast<CommonSymbol>(s)) {
-      if (size < common->size)
-        return s;
-    } else if (!isa<Undefined>(s)) {
-      error("TODO: implement common symbol resolution with other symbol kinds");
-      return s;
-    }
-  }
-
-  replaceSymbol<CommonSymbol>(s, name, file, size, align);
-  return s;
-}
-
 Symbol *SymbolTable::addDylib(StringRef name, DylibFile *file, bool isWeakDef,
                               bool isTlv) {
   Symbol *s;
diff --git a/lld/MachO/SymbolTable.h b/lld/MachO/SymbolTable.h
index b4c7ec8604ff..178b26f48599 100644
--- a/lld/MachO/SymbolTable.h
+++ b/lld/MachO/SymbolTable.h
@@ -19,7 +19,6 @@ namespace macho {
 
 class ArchiveFile;
 class DylibFile;
-class InputFile;
 class InputSection;
 class MachHeaderSection;
 class Symbol;
@@ -37,8 +36,6 @@ public:
 
   Symbol *addUndefined(StringRef name);
 
-  Symbol *addCommon(StringRef name, InputFile *, uint64_t size, uint32_t align);
-
   Symbol *addDylib(StringRef name, DylibFile *file, bool isWeakDef, bool isTlv);
 
   Symbol *addLazy(StringRef name, ArchiveFile *file,
diff --git a/lld/MachO/Symbols.h b/lld/MachO/Symbols.h
index 14c1ee813420..8feab5094f97 100644
--- a/lld/MachO/Symbols.h
+++ b/lld/MachO/Symbols.h
@@ -14,7 +14,6 @@
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Strings.h"
 #include "llvm/Object/Archive.h"
-#include "llvm/Support/MathExtras.h"
 
 namespace lld {
 namespace macho {
@@ -37,7 +36,6 @@ public:
   enum Kind {
     DefinedKind,
     UndefinedKind,
-    CommonKind,
     DylibKind,
     LazyKind,
     DSOHandleKind,
@@ -119,35 +117,6 @@ public:
   static bool classof(const Symbol *s) { return s->kind() == UndefinedKind; }
 };
 
-// On Unix, it is traditionally allowed to write variable definitions without
-// initialization expressions (such as "int foo;") to header files. These are
-// called tentative definitions.
-//
-// Using tentative definitions is usually considered a bad practice; you should
-// write only declarations (such as "extern int foo;") to header files.
-// Nevertheless, the linker and the compiler have to do something to support
-// bad code by allowing duplicate definitions for this particular case.
-//
-// The compiler creates common symbols when it sees tentative definitions.
-// (You can suppress this behavior and let the compiler create a regular
-// defined symbol by passing -fno-common.) When linking the final binary, if
-// there are remaining common symbols after name resolution is complete, the
-// linker converts them to regular defined symbols in a __common section.
-class CommonSymbol : public Symbol {
-public:
-  CommonSymbol(StringRefZ name, InputFile *file, uint64_t size, uint32_t align)
-      : Symbol(CommonKind, name), file(file), size(size),
-        align(align != 1 ? align : llvm::PowerOf2Ceil(size)) {
-    // TODO: cap maximum alignment
-  }
-
-  static bool classof(const Symbol *s) { return s->kind() == CommonKind; }
-
-  InputFile *const file;
-  const uint64_t size;
-  const uint32_t align;
-};
-
 class DylibSymbol : public Symbol {
 public:
   DylibSymbol(DylibFile *file, StringRefZ name, bool isWeakDef, bool isTlv)
@@ -216,10 +185,8 @@ public:
 union SymbolUnion {
   alignas(Defined) char a[sizeof(Defined)];
   alignas(Undefined) char b[sizeof(Undefined)];
-  alignas(CommonSymbol) char c[sizeof(CommonSymbol)];
-  alignas(DylibSymbol) char d[sizeof(DylibSymbol)];
-  alignas(LazySymbol) char e[sizeof(LazySymbol)];
-  alignas(DSOHandle) char f[sizeof(DSOHandle)];
+  alignas(DylibSymbol) char c[sizeof(DylibSymbol)];
+  alignas(LazySymbol) char d[sizeof(LazySymbol)];
 };
 
 template <typename T, typename... ArgT>
diff --git a/lld/MachO/SyntheticSections.h b/lld/MachO/SyntheticSections.h
index 55fd15ea8aff..90861839e4f3 100644
--- a/lld/MachO/SyntheticSections.h
+++ b/lld/MachO/SyntheticSections.h
@@ -26,7 +26,6 @@ namespace macho {
 namespace section_names {
 
 constexpr const char pageZero[] = "__pagezero";
-constexpr const char common[] = "__common";
 constexpr const char header[] = "__mach_header";
 constexpr const char binding[] = "__binding";
 constexpr const char weakBinding[] = "__weak_binding";