Make use of BSS more explicit in global initializers (vs a local .comm).

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the TargetLoweringX8632 class, which
@@ skipping 4645 matching lines @@
   IceString SectionSuffix = "";
   if (Ctx->getFlags().DataSections)
     SectionSuffix = "." + MangledName;
 
   Str << "\t.type\t" << MangledName << ",@object\n";
 
   if (IsConstant)
     Str << "\t.section\t.rodata" << SectionSuffix << ",\"a\",@progbits\n";
   else if (HasNonzeroInitializer)
     Str << "\t.section\t.data" << SectionSuffix << ",\"aw\",@progbits\n";
-  else if (IsExternal)
+  else
     Str << "\t.section\t.bss" << SectionSuffix << ",\"aw\",@nobits\n";
-  // No .section for non-constant + zeroinitializer + internal
 
   if (IsExternal)
     Str << "\t.globl\t" << MangledName << "\n";
-  else if (!IsConstant && !HasNonzeroInitializer)
-    Str << "\t.local\t" << MangledName << "\n";
-  // Internal symbols only get .local when using .comm.
 
-  if ((IsConstant || HasNonzeroInitializer || IsExternal) && Align > 1)
+  if (Align > 1)
     Str << "\t.align\t" << Align << "\n";
-  // Alignment is part of .comm.
 
-  if (IsConstant || HasNonzeroInitializer || IsExternal)
-    Str << MangledName << ":\n";
-  else
-    Str << "\t.comm\t" << MangledName << "," << Size << "," << Align << "\n";
+  Str << MangledName << ":\n";
 
   if (HasNonzeroInitializer) {
     for (VariableDeclaration::Initializer *Init : Initializers) {
       switch (Init->getKind()) {
       case VariableDeclaration::Initializer::DataInitializerKind: {
         const auto Data = llvm::cast<VariableDeclaration::DataInitializer>(Init)
                               ->getContents();
         for (SizeT i = 0; i < Init->getNumBytes(); ++i) {
           Str << "\t.byte\t" << (((unsigned)Data[i]) & 0xff) << "\n";
         }
@@ skipping 11 matching lines @@
           if (Offset >= 0 || (Offset == INT32_MIN))
             Str << " + " << Offset;
           else
             Str << " - " << -Offset;
         }
         Str << "\n";
         break;
       }
       }
     }
-  } else if (IsConstant || IsExternal)
+  } else
+    // NOTE: for non-constant zero initializers, this is BSS (no bits),
+    // so an ELF writer would not write to the file, and only track
+    // virtual offsets, but the .s writer still needs this .zero and
+    // cannot simply use the .size to advance offsets.
     Str << "\t.zero\t" << Size << "\n";
-  // Size is part of .comm.
 
-  if (IsConstant || HasNonzeroInitializer || IsExternal)
-    Str << "\t.size\t" << MangledName << ", " << Size << "\n";
-  // Size is part of .comm.
+  Str << "\t.size\t" << MangledName << ", " << Size << "\n";
 }
 
 } // end of namespace Ice