llvm-mc: Clean up some handling of symbol/section association to be more correct

(external was really undefined and there wasn't an explicit representation for
absolute symbols).
 - This still needs some cleanup to how the absolute "pseudo" section is dealt
   with, but I haven't figured out the nicest approach yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79733 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 14 insertions, 12 deletions

diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 3dfd8e9474..655137d580 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -107,14 +107,11 @@ void MCAsmStreamer::SwitchSection(const MCSection *Section) {
 }
 
 void MCAsmStreamer::EmitLabel(MCSymbol *Symbol) {
-  assert(Symbol->getSection() == 0 && "Cannot emit a symbol twice!");
+  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
   assert(CurSection && "Cannot emit before setting section!");
-  assert(!getContext().GetSymbolValue(Symbol) && 
-         "Cannot emit symbol which was directly assigned to!");
 
   OS << Symbol << ":\n";
-  Symbol->setSection(CurSection);
-  Symbol->setExternal(false);
+  Symbol->setSection(*CurSection);
 }
 
 void MCAsmStreamer::EmitAssemblerFlag(AssemblerFlag Flag) {
@@ -127,7 +124,9 @@ void MCAsmStreamer::EmitAssemblerFlag(AssemblerFlag Flag) {
 
 void MCAsmStreamer::EmitAssignment(MCSymbol *Symbol, const MCValue &Value,
                                    bool MakeAbsolute) {
-  assert(!Symbol->getSection() && "Cannot assign to a label!");
+  // Only absolute symbols can be redefined.
+  assert((Symbol->isUndefined() || Symbol->isAbsolute()) &&
+         "Cannot define a symbol twice!");
 
   if (MakeAbsolute) {
     OS << ".set " << Symbol << ", " << Value << '\n';
diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 316051ce01..421faef6aa 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -91,15 +91,12 @@ void MCMachOStreamer::SwitchSection(const MCSection *Section) {
 }
 
 void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
-  assert(Symbol->getSection() == 0 && "Cannot emit a symbol twice!");
+  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
   assert(CurSection && "Cannot emit before setting section!");
-  assert(!getContext().GetSymbolValue(Symbol) &&
-         "Cannot emit symbol which was directly assigned to!");
 
   llvm_unreachable("FIXME: Not yet implemented!");
 
-  Symbol->setSection(CurSection);
-  Symbol->setExternal(false);
+  Symbol->setSection(*CurSection);
 }
 
 void MCMachOStreamer::EmitAssemblerFlag(AssemblerFlag Flag) {
@@ -109,7 +106,9 @@ void MCMachOStreamer::EmitAssemblerFlag(AssemblerFlag Flag) {
 void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol,
                                      const MCValue &Value,
                                      bool MakeAbsolute) {
-  assert(!Symbol->getSection() && "Cannot assign to a label!");
+  // Only absolute symbols can be redefined.
+  assert((Symbol->isUndefined() || Symbol->isAbsolute()) &&
+         "Cannot define a symbol twice!");
 
   llvm_unreachable("FIXME: Not yet implemented!");
 }
diff --git a/lib/MC/MCSymbol.cpp b/lib/MC/MCSymbol.cpp
index d032017ca4..3c9894b691 100644
--- a/lib/MC/MCSymbol.cpp
+++ b/lib/MC/MCSymbol.cpp
@@ -12,6 +12,10 @@
 
 using namespace llvm;
 
+// Sentinel value for the absolute pseudo section.
+const MCSection *MCSymbol::AbsolutePseudoSection =
+  reinterpret_cast<const MCSection *>(1);
+
 /// NeedsQuoting - Return true if the string \arg Str needs quoting, i.e., it
 /// does not match [a-zA-Z_.][a-zA-Z0-9_.]*.
 //