Change MCExpr::EvaluateAsRelocatableImpl of variables to return the original

variable if recursing fails to simplify it.

Factor AliasedSymbol to be a method of MCSymbol.

Update MCAssembler::EvaluateFixup to match the change in
EvaluateAsRelocatableImpl.

Remove the WeakRefExpr hack, as the object writer now sees the weakref with
no extra effort needed.

Nothing else is using MCTargetExpr, but keep it for now.

Now that the ELF writer sees relocations with aliases, handle

    .weak    foo2
foo2:
    .weak    bar2
    .set    bar2,foo2
    .quad    bar2

the same way gas does and produce a relocation with bar2.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119152 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 60 insertions, 116 deletions

diff --git a/lib/MC/ELFObjectWriter.cpp b/lib/MC/ELFObjectWriter.cpp
index e11d68e..18d8e74 100644
--- a/lib/MC/ELFObjectWriter.cpp
+++ b/lib/MC/ELFObjectWriter.cpp
@@ -504,31 +504,6 @@ static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) {
   return 0;
 }
 
-static const MCSymbol &AliasedSymbol(const MCSymbol &Symbol) {
-  const MCSymbol *S = &Symbol;
-  while (S->isVariable()) {
-    const MCExpr *Value = S->getVariableValue();
-    MCExpr::ExprKind Kind = Value->getKind();
-    switch (Kind) {
-    case MCExpr::SymbolRef: {
-      const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
-      S = &Ref->getSymbol();
-      break;
-    }
-    case MCExpr::Target: {
-      const MCTargetExpr *TExp = static_cast<const MCTargetExpr*>(Value);
-      MCValue Res;
-      TExp->EvaluateAsRelocatableImpl(Res, NULL);
-      S = &Res.getSymA()->getSymbol();
-      break;
-    }
-    default:
-      return *S;
-    }
-  }
-  return *S;
-}
-
 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
   // The presence of symbol versions causes undefined symbols and
   // versions declared with @@@ to be renamed.
@@ -536,7 +511,7 @@ void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
   for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
          ie = Asm.symbol_end(); it != ie; ++it) {
     const MCSymbol &Alias = it->getSymbol();
-    const MCSymbol &Symbol = AliasedSymbol(Alias);
+    const MCSymbol &Symbol = Alias.AliasedSymbol();
     MCSymbolData &SD = Asm.getSymbolData(Symbol);
 
     // Not an alias.
@@ -572,7 +547,7 @@ void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
                                   const MCAsmLayout &Layout) {
   MCSymbolData &OrigData = *MSD.SymbolData;
   MCSymbolData &Data =
-    Layout.getAssembler().getSymbolData(AliasedSymbol(OrigData.getSymbol()));
+    Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol());
 
   bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() ||
     Data.getSymbol().isVariable();
@@ -673,28 +648,24 @@ const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm,
                                                const MCValue &Target,
                                                const MCFragment &F) const {
   const MCSymbol &Symbol = Target.getSymA()->getSymbol();
-  const MCSymbol &ASymbol = AliasedSymbol(Symbol);
-  const MCSymbol *RenamedP = Renames.lookup(&Symbol);
-
-  if (!RenamedP) {
-    if (Target.getSymA()->getKind() == MCSymbolRefExpr::VK_None ||
-        Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref)
-      RenamedP = &ASymbol;
-    else
-      RenamedP = &Symbol;
+  const MCSymbol &ASymbol = Symbol.AliasedSymbol();
+  const MCSymbol *Renamed = Renames.lookup(&Symbol);
+  const MCSymbolData &SD = Asm.getSymbolData(Symbol);
+
+  if (ASymbol.isUndefined()) {
+    if (Renamed)
+      return Renamed;
+    return &ASymbol;
   }
-  const MCSymbol &Renamed = *RenamedP;
-
-  MCSymbolData &SD = Asm.getSymbolData(Symbol);
-
-  if (Symbol.isUndefined())
-    return &Renamed;
 
-  if (SD.isExternal())
-    return &Renamed;
+  if (SD.isExternal()) {
+    if (Renamed)
+      return Renamed;
+    return &Symbol;
+  }
 
   const MCSectionELF &Section =
-    static_cast<const MCSectionELF&>(Symbol.getSection());
+    static_cast<const MCSectionELF&>(ASymbol.getSection());
 
   if (Section.getKind().isBSS())
     return NULL;
@@ -706,13 +677,18 @@ const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm,
   if (&Sec2 != &Section &&
       (Kind == MCSymbolRefExpr::VK_PLT ||
        Kind == MCSymbolRefExpr::VK_GOTPCREL ||
-       Kind == MCSymbolRefExpr::VK_GOTOFF))
-    return &Renamed;
+       Kind == MCSymbolRefExpr::VK_GOTOFF)) {
+    if (Renamed)
+      return Renamed;
+    return &Symbol;
+  }
 
   if (Section.getFlags() & MCSectionELF::SHF_MERGE) {
-    if (Target.getConstant() != 0)
-      return &Renamed;
-    return NULL;
+    if (Target.getConstant() == 0)
+      return NULL;
+    if (Renamed)
+      return Renamed;
+    return &Symbol;
   }
 
   return NULL;
@@ -742,7 +718,7 @@ static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
   if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
     return true;
 
-  const MCSymbol &A = AliasedSymbol(Symbol);
+  const MCSymbol &A = Symbol.AliasedSymbol();
   if (!A.isVariable() && A.isUndefined() && !Data.isCommon())
     return false;
 
@@ -761,7 +737,7 @@ static bool isLocal(const MCSymbolData &Data, bool isSignature,
     return false;
 
   const MCSymbol &Symbol = Data.getSymbol();
-  const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
+  const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
 
   if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
     if (isSignature && !isUsedInReloc)
@@ -830,7 +806,7 @@ void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
 
     ELFSymbolData MSD;
     MSD.SymbolData = it;
-    const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
+    const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
 
     // Undefined symbols are global, but this is the first place we
     // are able to set it.
@@ -1104,13 +1080,13 @@ bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
   const MCSection *SectionA = 0;
   const MCSymbol *SymbolA = 0;
   if (const MCSymbolRefExpr *A = Target.getSymA()) {
-    SymbolA = &A->getSymbol();
+    SymbolA = &A->getSymbol().AliasedSymbol();
     SectionA = &SymbolA->getSection();
   }
 
   const MCSection *SectionB = 0;
   if (const MCSymbolRefExpr *B = Target.getSymB()) {
-    SectionB = &B->getSymbol().getSection();
+    SectionB = &B->getSymbol().AliasedSymbol().getSection();
   }
 
   if (!BaseSection)
@@ -1413,6 +1389,7 @@ void X86ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
   int Index = 0;
   int64_t Value = Target.getConstant();
   const MCSymbol &Symbol = Target.getSymA()->getSymbol();
+  const MCSymbol &ASymbol = Symbol.AliasedSymbol();
   const MCSymbol *RelocSymbol = SymbolToReloc(Asm, Target, *Fragment);
 
   bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
@@ -1432,7 +1409,7 @@ void X86ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
     }
 
     if (!RelocSymbol) {
-      MCSymbolData &SD = Asm.getSymbolData(Symbol);
+      MCSymbolData &SD = Asm.getSymbolData(ASymbol);
       MCFragment *F = SD.getFragment();
 
       Index = F->getParent()->getOrdinal();
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 8e87d5b..c80dc3c 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -285,14 +285,16 @@ bool MCAssembler::EvaluateFixup(const MCObjectWriter &Writer,
     Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
   bool IsResolved = true;
   if (const MCSymbolRefExpr *A = Target.getSymA()) {
-    if (A->getSymbol().isDefined())
-      Value += Layout.getSymbolAddress(&getSymbolData(A->getSymbol()));
+    const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
+    if (Sym.isDefined())
+      Value += Layout.getSymbolAddress(&getSymbolData(Sym));
     else
       IsResolved = false;
   }
   if (const MCSymbolRefExpr *B = Target.getSymB()) {
-    if (B->getSymbol().isDefined())
-      Value -= Layout.getSymbolAddress(&getSymbolData(B->getSymbol()));
+    const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
+    if (Sym.isDefined())
+      Value -= Layout.getSymbolAddress(&getSymbolData(Sym));
     else
       IsResolved = false;
   }
diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index a2d94f5..157c0c0 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -240,49 +240,6 @@ void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
   Symbol->setVariableValue(AddValueSymbols(Value));
 }
 
-// This is a hack. To be able to implement weakrefs the writer has to be able
-// to distinguish
-//    .weakref foo, bar
-//    .long foo
-// from
-//   .weakref foo, bar
-//   .long bar
-// since the first case should produce a weak undefined reference and the second
-// one a strong one.
-// If we created foo as a regular alias pointing to bar (foo = bar), then
-// MCExpr::EvaluateAsRelocatable would recurse on foo and the writer would
-// never see it used in a relocation.
-// What we do is create a MCTargetExpr that when evaluated produces a symbol
-// ref to a temporary symbol. This temporary symbol in turn is a variable
-// that equals the original symbol (tmp = bar). With this hack the writer
-// gets a relocation with tmp and can correctly implement weak references.
-
-namespace {
-class WeakRefExpr : public MCTargetExpr {
-private:
-  const MCSymbolRefExpr *Alias;
-
-  explicit WeakRefExpr(const MCSymbolRefExpr *Alias_)
-    : MCTargetExpr(), Alias(Alias_) {}
-
-public:
-  virtual void PrintImpl(raw_ostream &OS) const {
-    llvm_unreachable("Unimplemented");
-  }
-
-  virtual bool EvaluateAsRelocatableImpl(MCValue &Res,
-                                         const MCAsmLayout *Layout) const {
-    Res = MCValue::get(Alias, 0, 0);
-    return true;
-  }
-
-  static const WeakRefExpr *Create(const MCSymbol *Alias, MCContext &Ctx) {
-    const MCSymbolRefExpr *A = MCSymbolRefExpr::Create(Alias, Ctx);
-    return new (Ctx) WeakRefExpr(A);
-  }
-};
-} // end anonymous namespace
-
 void MCELFStreamer::SwitchSection(const MCSection *Section) {
   const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
   if (Grp)
@@ -294,16 +251,7 @@ void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
   getAssembler().getOrCreateSymbolData(*Symbol);
   MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
   AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
-
-  // Create the alias that actually points to Symbol
-  const MCSymbolRefExpr *SymRef = MCSymbolRefExpr::Create(Symbol, getContext());
-  MCSymbol *RealAlias = getContext().CreateTempSymbol();
-  RealAlias->setVariableValue(SymRef);
-
-  MCSymbolData &RealAliasSD = getAssembler().getOrCreateSymbolData(*RealAlias);
-  RealAliasSD.setFlags(RealAliasSD.getFlags() | ELF_Other_Weakref);
-
-  const MCExpr *Value = WeakRefExpr::Create(RealAlias, getContext());
+  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
   Alias->setVariableValue(Value);
 }
 
diff --git a/lib/MC/MCExpr.cpp b/lib/MC/MCExpr.cpp
index b1617ec..eea736e 100644
--- a/lib/MC/MCExpr.cpp
+++ b/lib/MC/MCExpr.cpp
@@ -336,9 +336,14 @@ bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res,
     const MCSymbol &Sym = SRE->getSymbol();
 
     // Evaluate recursively if this is a variable.
-    if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None)
-      return Sym.getVariableValue()->EvaluateAsRelocatableImpl(Res, Layout,
-                                                               true);
+    if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None) {
+      bool Ret = Sym.getVariableValue()->EvaluateAsRelocatableImpl(Res, Layout,
+                                                                   true);
+      // If we failed to simplify this to a constant, let the target
+      // handle it.
+      if (Ret && !Res.getSymA() && !Res.getSymB())
+        return true;
+    }
 
     Res = MCValue::get(SRE, 0, 0);
     return true;
diff --git a/lib/MC/MCSymbol.cpp b/lib/MC/MCSymbol.cpp
index ebd3144..1c71f26 100644
--- a/lib/MC/MCSymbol.cpp
+++ b/lib/MC/MCSymbol.cpp
@@ -39,6 +39,18 @@ static bool NameNeedsQuoting(StringRef Str) {
   return false;
 }
 
+const MCSymbol &MCSymbol::AliasedSymbol() const {
+  const MCSymbol *S = this;
+  while (S->isVariable()) {
+    const MCExpr *Value = S->getVariableValue();
+    if (Value->getKind() != MCExpr::SymbolRef)
+      return *S;
+    const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
+    S = &Ref->getSymbol();
+  }
+  return *S;
+}
+
 void MCSymbol::setVariableValue(const MCExpr *Value) {
   assert(!IsUsed && "Cannot set a variable that has already been used.");
   assert(Value && "Invalid variable value!");