On ELF and COFF treat linker_private like private.

The linkers on these systems don't have anything special to do with these
symbols. Since the intent is for them to be absent from the final object,
just treat them as private.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197080 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAsmInfo.h

@@ -124,10 +124,12 @@ namespace llvm {
     /// file.
     const char *PrivateGlobalPrefix;         // Defaults to "L"
 
-    /// LinkerPrivateGlobalPrefix - This prefix is used for symbols that should
-    /// be passed through the assembler but be removed by the linker.  This
-    /// is "l" on Darwin, currently used for some ObjC metadata.
-    const char *LinkerPrivateGlobalPrefix;   // Defaults to ""
+    /// This prefix is used for symbols that should be passed through the
+    /// assembler but be removed by the linker.  This is 'l' on Darwin,
+    /// currently used for some ObjC metadata.
+    /// The default of "" meast that for this system a plain private symbol
+    /// should be used.
+    const char *LinkerPrivateGlobalPrefix;    // Defaults to "".
 
     /// InlineAsmStart/End - If these are nonempty, they contain a directive to
     /// emit before and after an inline assembly statement.
@@ -441,8 +443,13 @@ namespace llvm {
     const char *getPrivateGlobalPrefix() const {
       return PrivateGlobalPrefix;
     }
+    bool hasLinkerPrivateGlobalPrefix() const {
+      return LinkerPrivateGlobalPrefix[0] != '\0';
+    }
     const char *getLinkerPrivateGlobalPrefix() const {
-      return LinkerPrivateGlobalPrefix;
+      if (hasLinkerPrivateGlobalPrefix())
+        return LinkerPrivateGlobalPrefix;
+      return getPrivateGlobalPrefix();
     }
     const char *getInlineAsmStart() const {
       return InlineAsmStart;

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1175,7 +1175,7 @@ void AsmPrinter::EmitJumpTableInfo() {
     // before each jump table.  The first label is never referenced, but tells
     // the assembler and linker the extents of the jump table object.  The
     // second label is actually referenced by the code.
-    if (JTInDiffSection && MAI->getLinkerPrivateGlobalPrefix()[0])
+    if (JTInDiffSection && MAI->hasLinkerPrivateGlobalPrefix())
       // FIXME: This doesn't have to have any specific name, just any randomly
       // named and numbered 'l' label would work.  Simplify GetJTISymbol.
       OutStreamer.EmitLabel(GetJTISymbol(JTI, true));

test/CodeGen/X86/linker-private.ll

@@ -0,0 +1,10 @@
+; RUN: llc < %s -mtriple=x86_64-pc-linux | FileCheck --check-prefix=ELF %s
+; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck --check-prefix=MACHO %s
+
+@foo = linker_private global i32 42
+;ELF: {{^}}.Lfoo:
+;MACHO: {{^}}l_foo:
+
+define i32* @f() {
+  ret i32* @foo
+}