[DWARF][NFC] Prep for upcoming DWARF v5 string offsets table producer patch.

[wolfgangp]

Summary

This is in preparation for an upcoming patch to implement the producer side of DWARF v5 string offsets tables. We'd like to use AsmPrinter's emitDwarfStringOffsets() with a simple DwarfStringPoolEntry record in order to emit string offsets from the DwarfStringPool class directly. Currently the method only takes a DwarfStringPoolEntryRef, which is awkward to construct from a DwarfStringPoolEntry and would create unnecessary overhead.

[aprantl]

Could you please upload patches with more context in the future? git diff -U9999 is good :-)

[aprantl]

include/llvm/CodeGen/DwarfStringPoolEntry.h

44 ↗

(On Diff #129347)

Comment perhaps?

[wolfgangp]

In D41920#972755, @aprantl wrote:

Could you please upload patches with more context in the future? git diff -U9999 is good :-)

Yeah, sorry, I usually do that. Somehow I forgot to do it this time.
Thanks for the quick review.

include/llvm/CodeGen/DwarfStringPoolEntry.h

44 ↗

(On Diff #129347)

Mostly a convenience, so the caller doesn't have to puzzle the string pool entry together from its components. I add a comment before I commit.

llvm/trunk/include/llvm/CodeGen/AsmPrinter.h

public:
   void emitDwarfSymbolReference(const MCSymbol *Label,
                                 bool ForceOffset = false) const;
 
   /// Emit the 4-byte offset of a string from the start of its section.
   ///
   /// When possible, emit a DwarfStringPool section offset without any
   /// relocations, and without using the symbol.  Otherwise, defers to \a
   /// emitDwarfSymbolReference().
-  void emitDwarfStringOffset(DwarfStringPoolEntryRef S) const;
+  void emitDwarfStringOffset(DwarfStringPoolEntry S) const;
+
+  /// Emit the 4-byte offset of a string from the start of its section.
+  void emitDwarfStringOffset(DwarfStringPoolEntryRef S) const {
+    emitDwarfStringOffset(S.getEntry());
+  }
 
   /// Get the value for DW_AT_APPLE_isa. Zero if no isa encoding specified.
   virtual unsigned getISAEncoding() { return 0; }
 
   /// Emit the directive and value for debug thread local expression
   ///
   /// \p Value - The value to emit.
   /// \p Size - The size of the integer (in bytes) to emit.

llvm/trunk/include/llvm/CodeGen/DwarfStringPoolEntry.h

public:
   explicit operator bool() const { return I; }
   MCSymbol *getSymbol() const {
     assert(I->second.Symbol && "No symbol available!");
     return I->second.Symbol;
   }
   unsigned getOffset() const { return I->second.Offset; }
   unsigned getIndex() const { return I->second.Index; }
   StringRef getString() const { return I->first(); }
+  /// Return the entire string pool entry for convenience.
+  DwarfStringPoolEntry getEntry() const { return I->getValue(); }
 
   bool operator==(const DwarfStringPoolEntryRef &X) const { return I == X.I; }
   bool operator!=(const DwarfStringPoolEntryRef &X) const { return I != X.I; }
 };
 
 } // end namespace llvm
 
 #endif

llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp

if (MAI->doesDwarfUseRelocationsAcrossSections()) {
       return;
     }
   }
 
   // Otherwise, emit it as a label difference from the start of the section.
   EmitLabelDifference(Label, Label->getSection().getBeginSymbol(), 4);
 }
 
-void AsmPrinter::emitDwarfStringOffset(DwarfStringPoolEntryRef S) const {
+void AsmPrinter::emitDwarfStringOffset(DwarfStringPoolEntry S) const {
   if (MAI->doesDwarfUseRelocationsAcrossSections()) {
-    emitDwarfSymbolReference(S.getSymbol());
+    assert(S.Symbol && "No symbol available");
+    emitDwarfSymbolReference(S.Symbol);
     return;
   }
 
   // Just emit the offset directly; no need for symbol math.
-  EmitInt32(S.getOffset());
+  EmitInt32(S.Offset);
 }
 
 //===----------------------------------------------------------------------===//
 // Dwarf Lowering Routines
 //===----------------------------------------------------------------------===//
 
 void AsmPrinter::emitCFIInstruction(const MCCFIInstruction &Inst) const {
   switch (Inst.getOperation()) {