MC: For variable symbols, maintain MCSymbol::Section as a cache.

This fixes the visibility of symbols in certain edge cases involving aliases
with multiple levels of indirection.

Fixes PR19582.

Differential Revision: http://reviews.llvm.org/D8586

llvm-svn: 233595

4 files changed, 4 insertions, 29 deletions

diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index 8a64403362c..995f4c96ee6 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -775,6 +775,9 @@ const MCSection *MCExpr::FindAssociatedSection() const {
     if (RHS_S == MCSymbol::AbsolutePseudoSection)
       return LHS_S;
 
+    if (BE->getOpcode() == MCBinaryExpr::Sub)
+      return MCSymbol::AbsolutePseudoSection;
+
     // Otherwise, return the first non-null section.
     return LHS_S ? LHS_S : RHS_S;
   }
diff --git a/llvm/lib/MC/MCSymbol.cpp b/llvm/lib/MC/MCSymbol.cpp
index 24165254e56..6582574ae94 100644
--- a/llvm/lib/MC/MCSymbol.cpp
+++ b/llvm/lib/MC/MCSymbol.cpp
@@ -55,13 +55,7 @@ void MCSymbol::setVariableValue(const MCExpr *Value) {
   assert(!IsUsed && "Cannot set a variable that has already been used.");
   assert(Value && "Invalid variable value!");
   this->Value = Value;
-
-  // Variables should always be marked as in the same "section" as the value.
-  const MCSection *Section = Value->FindAssociatedSection();
-  if (Section)
-    setSection(*Section);
-  else
-    setUndefined();
+  this->Section = nullptr;
 }
 
 void MCSymbol::print(raw_ostream &OS) const {
diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
index 5e9e86f18a0..56cccab1d39 100644
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -649,33 +649,12 @@ void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
   }
 }
 
-void MachObjectWriter::markAbsoluteVariableSymbols(MCAssembler &Asm,
-                                                   const MCAsmLayout &Layout) {
-  for (MCSymbolData &SD : Asm.symbols()) {
-    if (!SD.getSymbol().isVariable())
-      continue;
-
-    // Is the variable is a symbol difference (SA - SB + C) expression,
-    // and neither symbol is external, mark the variable as absolute.
-    const MCExpr *Expr = SD.getSymbol().getVariableValue();
-    MCValue Value;
-    if (Expr->EvaluateAsRelocatable(Value, &Layout, nullptr)) {
-      if (Value.getSymA() && Value.getSymB())
-        const_cast<MCSymbol*>(&SD.getSymbol())->setAbsolute();
-    }
-  }
-}
-
 void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
                                                 const MCAsmLayout &Layout) {
   computeSectionAddresses(Asm, Layout);
 
   // Create symbol data for any indirect symbols.
   BindIndirectSymbols(Asm);
-
-  // Mark symbol difference expressions in variables (from .set or = directives)
-  // as absolute.
-  markAbsoluteVariableSymbols(Asm, Layout);
 }
 
 bool MachObjectWriter::
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
index f6033a7e157..a84f0585aea 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -523,7 +523,6 @@ void X86AsmPrinter::EmitStartOfAsmFile(Module &M) {
       // must be registered in .sxdata.  Use of any unregistered handlers will
       // cause the process to terminate immediately.  LLVM does not know how to
       // register any SEH handlers, so its object files should be safe.
-      S->setAbsolute();
       OutStreamer.EmitSymbolAttribute(S, MCSA_Global);
       OutStreamer.EmitAssignment(
           S, MCConstantExpr::Create(int64_t(1), MMI->getContext()));