MCExpr: Add FindAssociatedSection, which attempts to mirror the 'as' semantics

that associate sections with expressions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130517 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCExpr.h

@@ -19,6 +19,7 @@ class MCAsmInfo;
 class MCAsmLayout;
 class MCAssembler;
 class MCContext;
+class MCSection;
 class MCSectionData;
 class MCSymbol;
 class MCValue;
@@ -92,6 +93,12 @@ public:
   /// @result - True on success.
   bool EvaluateAsRelocatable(MCValue &Res, const MCAsmLayout &Layout) const;
 
+  /// FindAssociatedSection - Find the "associated section" for this expression,
+  /// which is currently defined as the absolute section for constants, or
+  /// otherwise the section associated with the first defined symbol in the
+  /// expression.
+  const MCSection *FindAssociatedSection() const;
+
   /// @}
 
   static bool classof(const MCExpr *) { return true; }
@@ -420,6 +427,7 @@ public:
   virtual bool EvaluateAsRelocatableImpl(MCValue &Res,
                                          const MCAsmLayout *Layout) const = 0;
   virtual void AddValueSymbols(MCAssembler *) const = 0;
+  virtual const MCSection *FindAssociatedSection() const = 0;
 
   static bool classof(const MCExpr *E) {
     return E->getKind() == MCExpr::Target;

include/llvm/MC/MCSymbol.h

@@ -56,6 +56,7 @@ namespace llvm {
     mutable unsigned IsUsed : 1;
 
   private:  // MCContext creates and uniques these.
+    friend class MCExpr;
     friend class MCContext;
     MCSymbol(StringRef name, bool isTemporary)
       : Name(name), Section(0), Value(0),

lib/MC/MCExpr.cpp

@@ -559,3 +559,45 @@ bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res,
   assert(0 && "Invalid assembly expression kind!");
   return false;
 }
+
+const MCSection *MCExpr::FindAssociatedSection() const {
+  switch (getKind()) {
+  case Target:
+    // We never look through target specific expressions.
+    return cast<MCTargetExpr>(this)->FindAssociatedSection();
+
+  case Constant:
+    return MCSymbol::AbsolutePseudoSection;
+
+  case SymbolRef: {
+    const MCSymbolRefExpr *SRE = cast<MCSymbolRefExpr>(this);
+    const MCSymbol &Sym = SRE->getSymbol();
+
+    if (Sym.isDefined())
+      return &Sym.getSection();
+
+    return 0;
+  }
+
+  case Unary:
+    return cast<MCUnaryExpr>(this)->getSubExpr()->FindAssociatedSection();
+
+  case Binary: {
+    const MCBinaryExpr *BE = cast<MCBinaryExpr>(this);
+    const MCSection *LHS_S = BE->getLHS()->FindAssociatedSection();
+    const MCSection *RHS_S = BE->getRHS()->FindAssociatedSection();
+
+    // If either section is absolute, return the other.
+    if (LHS_S == MCSymbol::AbsolutePseudoSection)
+      return RHS_S;
+    if (RHS_S == MCSymbol::AbsolutePseudoSection)
+      return LHS_S;
+
+    // Otherwise, return the first non-null section.
+    return LHS_S ? LHS_S : RHS_S;
+  }
+  }
+
+  assert(0 && "Invalid assembly expression kind!");
+  return 0;
+}

lib/Target/ARM/ARMMCExpr.h

@@ -60,6 +60,9 @@ public:
   bool EvaluateAsRelocatableImpl(MCValue &Res,
                                  const MCAsmLayout *Layout) const;
   void AddValueSymbols(MCAssembler *) const;
+  const MCSection *FindAssociatedSection() const {
+    return getSubExpr()->FindAssociatedSection();
+  }
 
   static bool classof(const MCExpr *E) {
     return E->getKind() == MCExpr::Target;