Produce .weak_def_can_be_hidden for some linkonce_odr values

With this patch llvm produces a weak_def_can_be_hidden for linkonce_odr
if they are also unnamed_addr or don't have their address taken.

There is not a lot of documentation about .weak_def_can_be_hidden, but
from the old discussion about linkonce_odr_auto_hide and the name of
the directive this looks correct: these symbols can be hidden.

Testing this with the ld64 in Xcode 5 linking clang reduces the number of
exported symbols from 21053 to 19049.

llvm-svn: 193718

3 files changed, 47 insertions, 8 deletions

diff --git a/llvm/include/llvm/CodeGen/AsmPrinter.h b/llvm/include/llvm/CodeGen/AsmPrinter.h
index d66665c85c9..4bda0f1603a 100644
--- a/llvm/include/llvm/CodeGen/AsmPrinter.h
+++ b/llvm/include/llvm/CodeGen/AsmPrinter.h
@@ -486,7 +486,7 @@ namespace llvm {
     void EmitVisibility(MCSymbol *Sym, unsigned Visibility,
                         bool IsDefinition = true) const;
 
-    void EmitLinkage(unsigned Linkage, MCSymbol *GVSym) const;
+    void EmitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const;
 
     void EmitJumpTableEntry(const MachineJumpTableInfo *MJTI,
                             const MachineBasicBlock *MBB, unsigned uid) const;
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 41d83beb5f2..9a024621651 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -48,6 +48,7 @@
 #include "llvm/Target/TargetLoweringObjectFile.h"
 #include "llvm/Target/TargetOptions.h"
 #include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
 using namespace llvm;
 
 static const char *const DWARFGroupName = "DWARF Emission";
@@ -212,9 +213,8 @@ bool AsmPrinter::doInitialization(Module &M) {
   llvm_unreachable("Unknown exception type.");
 }
 
-void AsmPrinter::EmitLinkage(unsigned L, MCSymbol *GVSym) const {
-  GlobalValue::LinkageTypes Linkage = (GlobalValue::LinkageTypes)L;
-
+void AsmPrinter::EmitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const {
+  GlobalValue::LinkageTypes Linkage = GV->getLinkage();
   switch (Linkage) {
   case GlobalValue::CommonLinkage:
   case GlobalValue::LinkOnceAnyLinkage:
@@ -227,7 +227,20 @@ void AsmPrinter::EmitLinkage(unsigned L, MCSymbol *GVSym) const {
       // .globl _foo
       OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
 
-      if (Linkage != GlobalValue::LinkOnceODRAutoHideLinkage)
+
+      bool CanBeHidden = Linkage == GlobalValue::LinkOnceODRAutoHideLinkage;
+
+      if (!CanBeHidden && Linkage == GlobalValue::LinkOnceODRLinkage) {
+        if (GV->hasUnnamedAddr()) {
+          CanBeHidden = true;
+        } else {
+          GlobalStatus GS;
+          if (!GlobalStatus::analyzeGlobal(GV, GS) && !GS.IsCompared)
+            CanBeHidden = true;
+        }
+      }
+
+      if (!CanBeHidden)
         // .weak_definition _foo
         OutStreamer.EmitSymbolAttribute(GVSym, MCSA_WeakDefinition);
       else
@@ -399,7 +412,7 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
 
     OutStreamer.SwitchSection(TLVSect);
     // Emit the linkage here.
-    EmitLinkage(GV->getLinkage(), GVSym);
+    EmitLinkage(GV, GVSym);
     OutStreamer.EmitLabel(GVSym);
 
     // Three pointers in size:
@@ -418,7 +431,7 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
 
   OutStreamer.SwitchSection(TheSection);
 
-  EmitLinkage(GV->getLinkage(), GVSym);
+  EmitLinkage(GV, GVSym);
   EmitAlignment(AlignLog, GV);
 
   OutStreamer.EmitLabel(GVSym);
@@ -444,7 +457,7 @@ void AsmPrinter::EmitFunctionHeader() {
   OutStreamer.SwitchSection(getObjFileLowering().SectionForGlobal(F, Mang, TM));
   EmitVisibility(CurrentFnSym, F->getVisibility());
 
-  EmitLinkage(F->getLinkage(), CurrentFnSym);
+  EmitLinkage(F, CurrentFnSym);
   EmitAlignment(MF->getAlignment(), F);
 
   if (MAI->hasDotTypeDotSizeDirective())
diff --git a/llvm/test/CodeGen/X86/weak_def_can_be_hidden.ll b/llvm/test/CodeGen/X86/weak_def_can_be_hidden.ll
new file mode 100644
index 00000000000..f78f3571cec
--- /dev/null
+++ b/llvm/test/CodeGen/X86/weak_def_can_be_hidden.ll
@@ -0,0 +1,26 @@
+; RUN: llc -mtriple=x86_64-apple-darwin  -O0 < %s | FileCheck %s
+
+@v1 = linkonce_odr global i32 32
+; CHECK: .globl  _v1
+; CHECK: .weak_def_can_be_hidden _v1
+
+define i32 @f1() {
+  %x = load i32 * @v1
+  ret i32 %x
+}
+
+@v2 = linkonce_odr global i32 32
+; CHECK: .globl  _v2
+; CHECK: .weak_definition _v2
+
+@v3 = linkonce_odr unnamed_addr global i32 32
+; CHECK: .globl  _v3
+; CHECK: .weak_def_can_be_hidden _v3
+
+define i32* @f2() {
+  ret i32* @v2
+}
+
+define i32* @f3() {
+  ret i32* @v3
+}