Rename and improve emitSectionOffset.

Different object formats represent references from dwarf in different ways.

ELF uses a relocation to the referenced point (except for .dwo) and
COFF/MachO use the offset of the referenced point inside its section.

This patch renames emitSectionOffset because

* It doesn't produce an offset on ELF.
* It changes behavior depending on how DWARF is represented, so adding
dwarf to its name is probably a good thing.

The patch also adds an option to force the use of offsets.That avoids
funny looking code like

  if (!UseOffsets)
    Asm->emitSectionOffset....

It was correct, but read as if the ! was inverted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239866 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/AsmPrinter.h

@@ -418,16 +418,17 @@ public:
   /// Emit reference to a ttype global with a specified encoding.
   void EmitTTypeReference(const GlobalValue *GV, unsigned Encoding) const;
 
-  /// Emit the 4-byte offset of Label from the start of its section.  This can
-  /// be done with a special directive if the target supports it (e.g. cygwin)
-  /// or by emitting it as an offset from a label at the start of the section.
-  void emitSectionOffset(const MCSymbol *Label) const;
+  /// Emit a reference to a symbol for use in dwarf. Different object formats
+  /// represent this in different ways. Some use a relocation others encode
+  /// the label offset in its section.
+  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
-  /// emitSectionOffset().
+  /// emitDwarfSymbolReference().
   void emitDwarfStringOffset(DwarfStringPoolEntryRef S) const;
 
   /// Get the value for DW_AT_APPLE_isa. Zero if no isa encoding specified.

lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp

@@ -157,24 +157,20 @@ void AsmPrinter::EmitTTypeReference(const GlobalValue *GV,
     OutStreamer->EmitIntValue(0, GetSizeOfEncodedValue(Encoding));
 }
 
-/// EmitSectionOffset - Emit the 4-byte offset of Label from the start of its
-/// section.  This can be done with a special directive if the target supports
-/// it (e.g. cygwin) or by emitting it as an offset from a label at the start
-/// of the section.
-///
-/// SectionLabel is a temporary label emitted at the start of the section that
-/// Label lives in.
-void AsmPrinter::emitSectionOffset(const MCSymbol *Label) const {
-  // On COFF targets, we have to emit the special .secrel32 directive.
-  if (MAI->needsDwarfSectionOffsetDirective()) {
-    OutStreamer->EmitCOFFSecRel32(Label);
-    return;
-  }
+void AsmPrinter::emitDwarfSymbolReference(const MCSymbol *Label,
+                                          bool ForceOffset) const {
+  if (!ForceOffset) {
+    // On COFF targets, we have to emit the special .secrel32 directive.
+    if (MAI->needsDwarfSectionOffsetDirective()) {
+      OutStreamer->EmitCOFFSecRel32(Label);
+      return;
+    }
 
-  // If the format uses relocations with dwarf, refer to the symbol directly.
-  if (MAI->doesDwarfUseRelocationsAcrossSections()) {
-    OutStreamer->EmitSymbolValue(Label, 4);
-    return;
+    // If the format uses relocations with dwarf, refer to the symbol directly.
+    if (MAI->doesDwarfUseRelocationsAcrossSections()) {
+      OutStreamer->EmitSymbolValue(Label, 4);
+      return;
+    }
   }
 
   // Otherwise, emit it as a label difference from the start of the section.
@@ -183,7 +179,7 @@ void AsmPrinter::emitSectionOffset(const MCSymbol *Label) const {
 
 void AsmPrinter::emitDwarfStringOffset(DwarfStringPoolEntryRef S) const {
   if (MAI->doesDwarfUseRelocationsAcrossSections()) {
-    emitSectionOffset(S.getSymbol());
+    emitDwarfSymbolReference(S.getSymbol());
     return;
   }
 

lib/CodeGen/AsmPrinter/DIE.cpp

@@ -618,11 +618,7 @@ unsigned DIELocList::SizeOf(const AsmPrinter *AP, dwarf::Form Form) const {
 void DIELocList::EmitValue(const AsmPrinter *AP, dwarf::Form Form) const {
   DwarfDebug *DD = AP->getDwarfDebug();
   MCSymbol *Label = DD->getDebugLocs().getList(Index).Label;
-
-  if (AP->MAI->doesDwarfUseRelocationsAcrossSections() && !DD->useSplitDwarf())
-    AP->emitSectionOffset(Label);
-  else
-    AP->EmitLabelDifference(Label, Label->getSection().getBeginSymbol(), 4);
+  AP->emitDwarfSymbolReference(Label, /*ForceOffset*/ DD->useSplitDwarf());
 }
 
 #ifndef NDEBUG

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1414,7 +1414,7 @@ void DwarfDebug::emitDebugPubSection(
     Asm->EmitInt16(dwarf::DW_PUBNAMES_VERSION);
 
     Asm->OutStreamer->AddComment("Offset of Compilation Unit Info");
-    Asm->emitSectionOffset(TheU->getLabelBegin());
+    Asm->emitDwarfSymbolReference(TheU->getLabelBegin());
 
     Asm->OutStreamer->AddComment("Compilation Unit Length");
     Asm->EmitInt32(TheU->getLength());
@@ -1739,7 +1739,7 @@ void DwarfDebug::emitDebugARanges() {
     Asm->OutStreamer->AddComment("DWARF Arange version number");
     Asm->EmitInt16(dwarf::DW_ARANGES_VERSION);
     Asm->OutStreamer->AddComment("Offset Into Debug Info Section");
-    Asm->emitSectionOffset(CU->getLabelBegin());
+    Asm->emitDwarfSymbolReference(CU->getLabelBegin());
     Asm->OutStreamer->AddComment("Address Size (in bytes)");
     Asm->EmitInt8(PtrSize);
     Asm->OutStreamer->AddComment("Segment Size (in bytes)");

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -1449,10 +1449,8 @@ void DwarfUnit::emitHeader(bool UseOffsets) {
   // start of the section. Use a relocatable offset where needed to ensure
   // linking doesn't invalidate that offset.
   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
-  if (!UseOffsets)
-    Asm->emitSectionOffset(TLOF.getDwarfAbbrevSection()->getBeginSymbol());
-  else
-    Asm->EmitInt32(0);
+  Asm->emitDwarfSymbolReference(TLOF.getDwarfAbbrevSection()->getBeginSymbol(),
+                                UseOffsets);
 
   Asm->OutStreamer->AddComment("Address Size (in bytes)");
   Asm->EmitInt8(Asm->getDataLayout().getPointerSize());