Fix pr19645.

The fix itself is fairly simple: move getAccessVariant to MCValue so that we
replace the old weak expression evaluation with the far more general
EvaluateAsRelocatable.

This then requires that EvaluateAsRelocatable stop when it finds a non
trivial reference kind. And that in turn requires the ELF writer to look
harder for weak references.

Last but not least, this found a case where we were being bug by bug
compatible with gas and accepting an invalid input. I reported pr19647
to track it.

llvm-svn: 207920

9 files changed, 47 insertions, 53 deletions

diff --git a/llvm/lib/MC/CMakeLists.txt b/llvm/lib/MC/CMakeLists.txt
index 7b69c7a9e36..6a384c1a8e1 100644
--- a/llvm/lib/MC/CMakeLists.txt
+++ b/llvm/lib/MC/CMakeLists.txt
@@ -16,7 +16,6 @@ add_llvm_library(LLVMMC
   MCELF.cpp
   MCELFObjectTargetWriter.cpp
   MCELFStreamer.cpp
-  MCFixup.cpp
   MCFunction.cpp
   MCExpr.cpp
   MCExternalSymbolizer.cpp
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 3bce1211920..0a54627f8cd 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -787,6 +787,25 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
   return false;
 }
 
+static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
+  const MCSymbol &Sym = Ref.getSymbol();
+
+  if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
+    return &Sym;
+
+  if (!Sym.isVariable())
+    return nullptr;
+
+  const MCExpr *Expr = Sym.getVariableValue();
+  const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
+  if (!Inner)
+    return nullptr;
+
+  if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
+    return &Inner->getSymbol();
+  return nullptr;
+}
+
 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
                                        const MCAsmLayout &Layout,
                                        const MCFragment *Fragment,
@@ -872,8 +891,8 @@ void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
     if (const MCSymbol *R = Renames.lookup(SymA))
       SymA = R;
 
-    if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
-      WeakrefUsedInReloc.insert(SymA);
+    if (const MCSymbol *WeakRef = getWeakRef(*RefA))
+      WeakrefUsedInReloc.insert(WeakRef);
     else
       UsedInReloc.insert(SymA);
   }
diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index 60b14ad53ee..ff5009f0a20 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -658,12 +658,11 @@ bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
 
   case SymbolRef: {
     const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
-    bool IsWeakRef = SRE->getKind() == MCSymbolRefExpr::VK_WEAKREF;
     const MCSymbol &Sym = SRE->getSymbol();
     const MCAsmInfo &MCAsmInfo = SRE->getMCAsmInfo();
 
     // Evaluate recursively if this is a variable.
-    if (Sym.isVariable() && !IsWeakRef) {
+    if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None) {
       if (Sym.getVariableValue()->EvaluateAsRelocatableImpl(
               Res, Asm, Layout, Addrs, true, ForceVarExpansion)) {
         const MCSymbolRefExpr *A = Res.getSymA();
diff --git a/llvm/lib/MC/MCFixup.cpp b/llvm/lib/MC/MCFixup.cpp
deleted file mode 100644
index e41e67350c5..00000000000
--- a/llvm/lib/MC/MCFixup.cpp
+++ /dev/null
@@ -1,42 +0,0 @@
-//===- MCFixup.cpp - Assembly Fixup Implementation ------------------------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/MC/MCFixup.h"
-using namespace llvm;
-
-static MCSymbolRefExpr::VariantKind getAccessVariant(const MCExpr *Expr) {
-  switch (Expr->getKind()) {
-  case MCExpr::Unary: {
-    assert(getAccessVariant(cast<MCUnaryExpr>(Expr)->getSubExpr()) ==
-           MCSymbolRefExpr::VK_None);
-    return MCSymbolRefExpr::VK_None;
-  }
-
-  case MCExpr::Target:
-    llvm_unreachable("unsupported");
-
-  case MCExpr::Constant:
-    return MCSymbolRefExpr::VK_None;
-
-  case MCExpr::SymbolRef: {
-    const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(Expr);
-    return SRE->getKind();
-  }
-  case MCExpr::Binary: {
-    const MCBinaryExpr *ABE = cast<MCBinaryExpr>(Expr);
-    assert(getAccessVariant(ABE->getRHS()) == MCSymbolRefExpr::VK_None);
-    return getAccessVariant(ABE->getLHS());
-  }
-  }
-  llvm_unreachable("unknown MCExpr kind");
-}
-
-MCSymbolRefExpr::VariantKind MCFixup::getAccessVariant() const {
-  return ::getAccessVariant(getValue());
-}
diff --git a/llvm/lib/MC/MCValue.cpp b/llvm/lib/MC/MCValue.cpp
index 21d9e2102e2..9dfc56ef23d 100644
--- a/llvm/lib/MC/MCValue.cpp
+++ b/llvm/lib/MC/MCValue.cpp
@@ -10,6 +10,7 @@
 #include "llvm/MC/MCValue.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
@@ -41,3 +42,20 @@ void MCValue::dump() const {
   print(dbgs(), nullptr);
 }
 #endif
+
+MCSymbolRefExpr::VariantKind MCValue::getAccessVariant() const {
+  const MCSymbolRefExpr *B = getSymB();
+  if (B) {
+    if (B->getKind() != MCSymbolRefExpr::VK_None)
+      llvm_unreachable("unsupported");
+  }
+
+  const MCSymbolRefExpr *A = getSymA();
+  if (!A)
+    return MCSymbolRefExpr::VK_None;
+
+  MCSymbolRefExpr::VariantKind Kind = A->getKind();
+  if (Kind == MCSymbolRefExpr::VK_WEAKREF)
+    return MCSymbolRefExpr::VK_None;
+  return Kind;
+}
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
index a6f7258e651..1c842633f43 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
@@ -74,7 +74,7 @@ unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
 unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
                                                const MCFixup &Fixup,
                                                bool IsPCRel) const  {
-  MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
+  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
 
   unsigned Type = 0;
   if (IsPCRel) {
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCELFObjectWriter.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCELFObjectWriter.cpp
index d19f6a0214d..cd3b4f45359 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCELFObjectWriter.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCELFObjectWriter.cpp
@@ -41,11 +41,12 @@ PPCELFObjectWriter::PPCELFObjectWriter(bool Is64Bit, uint8_t OSABI)
 PPCELFObjectWriter::~PPCELFObjectWriter() {
 }
 
-static MCSymbolRefExpr::VariantKind getAccessVariant(const MCFixup &Fixup) {
+static MCSymbolRefExpr::VariantKind getAccessVariant(const MCValue &Target,
+                                                     const MCFixup &Fixup) {
   const MCExpr *Expr = Fixup.getValue();
 
   if (Expr->getKind() != MCExpr::Target)
-    return Fixup.getAccessVariant();
+    return Target.getAccessVariant();
 
   switch (cast<PPCMCExpr>(Expr)->getKind()) {
   case PPCMCExpr::VK_PPC_None:
@@ -72,7 +73,7 @@ unsigned PPCELFObjectWriter::getRelocTypeInner(const MCValue &Target,
                                                const MCFixup &Fixup,
                                                bool IsPCRel) const
 {
-  MCSymbolRefExpr::VariantKind Modifier = getAccessVariant(Fixup);
+  MCSymbolRefExpr::VariantKind Modifier = getAccessVariant(Target, Fixup);
 
   // determine the type of the relocation
   unsigned Type;
diff --git a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
index 54c6987ca2f..c6a18165889 100644
--- a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
+++ b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
@@ -82,7 +82,7 @@ static unsigned getPLTReloc(unsigned Kind) {
 unsigned SystemZObjectWriter::GetRelocType(const MCValue &Target,
                                            const MCFixup &Fixup,
                                            bool IsPCRel) const {
-  MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
+  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
   unsigned Kind = Fixup.getKind();
   switch (Modifier) {
   case MCSymbolRefExpr::VK_None:
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
index c4a1af86157..3fdec874cba 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
@@ -43,7 +43,7 @@ unsigned X86ELFObjectWriter::GetRelocType(const MCValue &Target,
                                           bool IsPCRel) const {
   // determine the type of the relocation
 
-  MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
+  MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
   unsigned Type;
   if (getEMachine() == ELF::EM_X86_64) {
     if (IsPCRel) {