IR: Do not consider available_externally linkage to be linker-weak.

From the linker's perspective, an available_externally global is equivalent
to an external declaration (per isDeclarationForLinker()), so it is incorrect
to consider it to be a weak definition.

Also clean up some logic in the dead argument elimination pass and clarify
its comments to better explain how its behavior depends on linkage,
introduce GlobalValue::isStrongDefinitionForLinker() and start using
it throughout the optimizers and backend.

Differential Revision: http://reviews.llvm.org/D10941

llvm-svn: 241413

10 files changed, 32 insertions, 49 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
index 554826b1e08..c88b559d1d5 100644
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
@@ -57,7 +57,7 @@ AArch64Subtarget::AArch64Subtarget(const Triple &TT, const std::string &CPU,
 unsigned char
 AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
                                         const TargetMachine &TM) const {
-  bool isDecl = GV->isDeclarationForLinker();
+  bool isDef = GV->isStrongDefinitionForLinker();
 
   // MachO large model always goes via a GOT, simply to get a single 8-byte
   // absolute relocation on all global addresses.
@@ -66,8 +66,7 @@ AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
 
   // The small code mode's direct accesses use ADRP, which cannot necessarily
   // produce the value 0 (if the code is above 4GB).
-  if (TM.getCodeModel() == CodeModel::Small &&
-      GV->isWeakForLinker() && isDecl) {
+  if (TM.getCodeModel() == CodeModel::Small && GV->hasExternalWeakLinkage()) {
     // In PIC mode use the GOT, but in absolute mode use a constant pool load.
     if (TM.getRelocationModel() == Reloc::Static)
         return AArch64II::MO_CONSTPOOL;
@@ -85,8 +84,7 @@ AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
   //     defined could end up in unexpected places. Use a GOT.
   if (TM.getRelocationModel() != Reloc::Static && GV->hasDefaultVisibility()) {
     if (isTargetMachO())
-      return (isDecl || GV->isWeakForLinker()) ? AArch64II::MO_GOT
-                                               : AArch64II::MO_NO_FLAG;
+      return isDef ? AArch64II::MO_NO_FLAG : AArch64II::MO_GOT;
     else
       // No need to go through the GOT for local symbols on ELF.
       return GV->hasLocalLinkage() ? AArch64II::MO_NO_FLAG : AArch64II::MO_GOT;
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index ba109e61982..607ce767be2 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -1734,12 +1734,12 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   } else if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
     const GlobalValue *GV = G->getGlobal();
     isDirect = true;
-    bool isExt = GV->isDeclaration() || GV->isWeakForLinker();
-    bool isStub = (isExt && Subtarget->isTargetMachO()) &&
+    bool isDef = GV->isStrongDefinitionForLinker();
+    bool isStub = (!isDef && Subtarget->isTargetMachO()) &&
                    getTargetMachine().getRelocationModel() != Reloc::Static;
     isARMFunc = !Subtarget->isThumb() || (isStub && !Subtarget->isMClass());
     // ARM call to a local ARM function is predicable.
-    isLocalARMFunc = !Subtarget->isThumb() && (!isExt || !ARMInterworking);
+    isLocalARMFunc = !Subtarget->isThumb() && (isDef || !ARMInterworking);
     // tBX takes a register source operand.
     if (isStub && Subtarget->isThumb1Only() && !Subtarget->hasV5TOps()) {
       assert(Subtarget->isTargetMachO() && "WrapperPIC use on non-MachO?");
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.cpp b/llvm/lib/Target/ARM/ARMSubtarget.cpp
index 55808dfb9ef..af18eeabf0e 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.cpp
+++ b/llvm/lib/Target/ARM/ARMSubtarget.cpp
@@ -286,7 +286,7 @@ ARMSubtarget::GVIsIndirectSymbol(const GlobalValue *GV,
   if (RelocM == Reloc::Static)
     return false;
 
-  bool isDecl = GV->isDeclarationForLinker();
+  bool isDef = GV->isStrongDefinitionForLinker();
 
   if (!isTargetMachO()) {
     // Extra load is needed for all externally visible.
@@ -294,34 +294,22 @@ ARMSubtarget::GVIsIndirectSymbol(const GlobalValue *GV,
       return false;
     return true;
   } else {
-    if (RelocM == Reloc::PIC_) {
-      // If this is a strong reference to a definition, it is definitely not
-      // through a stub.
-      if (!isDecl && !GV->isWeakForLinker())
-        return false;
-
-      // Unless we have a symbol with hidden visibility, we have to go through a
-      // normal $non_lazy_ptr stub because this symbol might be resolved late.
-      if (!GV->hasHiddenVisibility())  // Non-hidden $non_lazy_ptr reference.
-        return true;
+    // If this is a strong reference to a definition, it is definitely not
+    // through a stub.
+    if (isDef)
+      return false;
+
+    // Unless we have a symbol with hidden visibility, we have to go through a
+    // normal $non_lazy_ptr stub because this symbol might be resolved late.
+    if (!GV->hasHiddenVisibility())  // Non-hidden $non_lazy_ptr reference.
+      return true;
 
+    if (RelocM == Reloc::PIC_) {
       // If symbol visibility is hidden, we have a stub for common symbol
       // references and external declarations.
-      if (isDecl || GV->hasCommonLinkage())
+      if (GV->isDeclarationForLinker() || GV->hasCommonLinkage())
         // Hidden $non_lazy_ptr reference.
         return true;
-
-      return false;
-    } else {
-      // If this is a strong reference to a definition, it is definitely not
-      // through a stub.
-      if (!isDecl && !GV->isWeakForLinker())
-        return false;
-
-      // Unless we have a symbol with hidden visibility, we have to go through a
-      // normal $non_lazy_ptr stub because this symbol might be resolved late.
-      if (!GV->hasHiddenVisibility())  // Non-hidden $non_lazy_ptr reference.
-        return true;
     }
   }
 
diff --git a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
index 87a5236e711..adcf8ee8291 100644
--- a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
+++ b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
@@ -197,7 +197,7 @@ void PPCAsmPrinter::printOperand(const MachineInstr *MI, unsigned OpNo,
 
     // External or weakly linked global variables need non-lazily-resolved stubs
     if (TM.getRelocationModel() != Reloc::Static &&
-        (GV->isDeclaration() || GV->isWeakForLinker())) {
+        !GV->isStrongDefinitionForLinker()) {
       if (!GV->hasHiddenVisibility()) {
         SymToPrint = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr");
         MachineModuleInfoImpl::StubValueTy &StubSym = 
@@ -624,7 +624,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
       IsExternal = GV->isDeclaration();
       IsCommon = GV->hasCommonLinkage();
       IsNonLocalFunction = GV->getType()->getElementType()->isFunctionTy() &&
-        (GV->isDeclaration() || GV->isWeakForLinker());
+        !GV->isStrongDefinitionForLinker();
       IsAvailExt = GV->hasAvailableExternallyLinkage();
     } else if (MO.isCPI())
       MOSymbol = GetCPISymbol(MO.getIndex());
@@ -706,7 +706,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
       MOSymbol = getSymbol(GV);
       IsExternal = GV->isDeclaration();
       IsNonLocalFunction = GV->getType()->getElementType()->isFunctionTy() &&
-        (GV->isDeclaration() || GV->isWeakForLinker());
+        !GV->isStrongDefinitionForLinker();
     } else if (MO.isCPI())
       MOSymbol = GetCPISymbol(MO.getIndex());
 
diff --git a/llvm/lib/Target/PowerPC/PPCFastISel.cpp b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
index fafcd76f9d1..ac59542cb7a 100644
--- a/llvm/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
@@ -1979,7 +1979,7 @@ unsigned PPCFastISel::PPCMaterializeGV(const GlobalValue *GV, MVT VT) {
     // on the "if" path here.
     if (CModel == CodeModel::Large ||
         (GV->getType()->getElementType()->isFunctionTy() &&
-         (GV->isDeclaration() || GV->isWeakForLinker())) ||
+         !GV->isStrongDefinitionForLinker()) ||
         GV->isDeclaration() || GV->hasCommonLinkage() ||
         GV->hasAvailableExternallyLinkage())
       BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(PPC::LDtocL),
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index c85c2610d2f..7004a805a96 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -2901,7 +2901,7 @@ SDNode *PPCDAGToDAGISel::Select(SDNode *N) {
     if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
       const GlobalValue *GValue = G->getGlobal();
       if ((GValue->getType()->getElementType()->isFunctionTy() &&
-           (GValue->isDeclaration() || GValue->isWeakForLinker())) ||
+           !GValue->isStrongDefinitionForLinker()) ||
           GValue->isDeclaration() || GValue->hasCommonLinkage() ||
           GValue->hasAvailableExternallyLinkage())
         return transferMemOperands(N, CurDAG->getMachineNode(PPC::LDtocL, dl,
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 76ff04e1958..303d935b477 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -4084,8 +4084,7 @@ unsigned PrepareCall(SelectionDAG &DAG, SDValue &Callee, SDValue &InFlag,
     if ((DAG.getTarget().getRelocationModel() != Reloc::Static &&
          (Subtarget.getTargetTriple().isMacOSX() &&
           Subtarget.getTargetTriple().isMacOSXVersionLT(10, 5)) &&
-         (G->getGlobal()->isDeclaration() ||
-          G->getGlobal()->isWeakForLinker())) ||
+         !G->getGlobal()->isStrongDefinitionForLinker()) ||
         (Subtarget.isTargetELF() && !isPPC64 &&
          !G->getGlobal()->hasLocalLinkage() &&
          DAG.getTarget().getRelocationModel() == Reloc::PIC_)) {
@@ -4254,8 +4253,7 @@ static
 bool isLocalCall(const SDValue &Callee)
 {
   if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee))
-    return !G->getGlobal()->isDeclaration() &&
-           !G->getGlobal()->isWeakForLinker();
+    return G->getGlobal()->isStrongDefinitionForLinker();
   return false;
 }
 
diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 02645460b6a..0e2b1d31f04 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -3108,7 +3108,7 @@ bool X86FastISel::fastLowerCall(CallLoweringInfo &CLI) {
         GV->hasDefaultVisibility() && !GV->hasLocalLinkage()) {
       OpFlags = X86II::MO_PLT;
     } else if (Subtarget->isPICStyleStubAny() &&
-               (GV->isDeclaration() || GV->isWeakForLinker()) &&
+               !GV->isStrongDefinitionForLinker() &&
                (!Subtarget->getTargetTriple().isMacOSX() ||
                 Subtarget->getTargetTriple().isMacOSXVersionLT(10, 5))) {
       // PC-relative references to external symbols should go through $stub,
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index ee6785fd953..74d8e2187a6 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3109,7 +3109,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
           GV->hasDefaultVisibility() && !GV->hasLocalLinkage()) {
         OpFlags = X86II::MO_PLT;
       } else if (Subtarget->isPICStyleStubAny() &&
-                 (GV->isDeclaration() || GV->isWeakForLinker()) &&
+                 !GV->isStrongDefinitionForLinker() &&
                  (!Subtarget->getTargetTriple().isMacOSX() ||
                   Subtarget->getTargetTriple().isMacOSXVersionLT(10, 5))) {
         // PC-relative references to external symbols should go through $stub,
diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 3b25d30dc22..8076443795d 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -68,7 +68,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
   if (GV->hasDLLImportStorageClass())
     return X86II::MO_DLLIMPORT;
 
-  bool isDecl = GV->isDeclarationForLinker();
+  bool isDef = GV->isStrongDefinitionForLinker();
 
   // X86-64 in PIC mode.
   if (isPICStyleRIPRel()) {
@@ -80,8 +80,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
       // If symbol visibility is hidden, the extra load is not needed if
       // target is x86-64 or the symbol is definitely defined in the current
       // translation unit.
-      if (GV->hasDefaultVisibility() &&
-          (isDecl || GV->isWeakForLinker()))
+      if (GV->hasDefaultVisibility() && !isDef)
         return X86II::MO_GOTPCREL;
     } else if (!isTargetWin64()) {
       assert(isTargetELF() && "Unknown rip-relative target");
@@ -107,7 +106,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
 
     // If this is a strong reference to a definition, it is definitely not
     // through a stub.
-    if (!isDecl && !GV->isWeakForLinker())
+    if (isDef)
       return X86II::MO_PIC_BASE_OFFSET;
 
     // Unless we have a symbol with hidden visibility, we have to go through a
@@ -117,7 +116,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
 
     // If symbol visibility is hidden, we have a stub for common symbol
     // references and external declarations.
-    if (isDecl || GV->hasCommonLinkage()) {
+    if (GV->isDeclarationForLinker() || GV->hasCommonLinkage()) {
       // Hidden $non_lazy_ptr reference.
       return X86II::MO_DARWIN_HIDDEN_NONLAZY_PIC_BASE;
     }
@@ -131,7 +130,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
 
     // If this is a strong reference to a definition, it is definitely not
     // through a stub.
-    if (!isDecl && !GV->isWeakForLinker())
+    if (isDef)
       return X86II::MO_NO_FLAG;
 
     // Unless we have a symbol with hidden visibility, we have to go through a