[Debug-Info] [NFC] move emitDwarfUnitLength to MCStreamer class

[shchenz]

Summary

We may need to do some customization for DWARF unit length in DWARF section headers for some code generation path.
For example in D95518, for XCOFF in assembly path, AIX assembler does not require the debug section containing its debug unit length in the header.

Thanks to @ikudrin comments, moving the emitDwarfUnitLength to class MCStreamer can make us avoid the streamer type check in general code.

This is the NFC part to make D95518 easy to review.
Override of emitDwarfUnitLength in MCAsmStreamer class will be added in D95518.

[ikudrin]

llvm/unittests/CodeGen/AsmPrinterDwarfTest.cpp

296–297

This test file is for methods of AsmPrinter; other classes should be tested elsewhere. As the patch removes AsmPrinter::maybeEmitDwarf64Mark(), the corresponding tests can also be removed. That will not degrade the test coverage because MCStreamer::maybeEmitDwarf64Mark() is tested, although indirectly, in other tests.

[shchenz]

update:
1: delete unittest for maybeEmitDwarf64Mark in AsmPrinter class as now maybeEmitDwarf64Mark is not a member function of AsmPrinter

llvm/unittests/CodeGen/AsmPrinterDwarfTest.cpp

296–297

Make sense. Updated. Thanks.

[ikudrin]

llvm/unittests/CodeGen/AsmPrinterDwarfTest.cpp

296–297

The fixture class should also be removed as it now contains no tests.

[shchenz]

update:
1: remove the fixture class as well

llvm/unittests/CodeGen/AsmPrinterDwarfTest.cpp

296–297

opps, updated.

[ikudrin]

LGTM but please postpone committing it until the whole set of patches is completed so we can have a full image of the changes.

[shchenz]

In D95932#2541452, @ikudrin wrote:

LGTM but please postpone committing it until the whole set of patches is completed so we can have a full image of the changes.

Thanks for your review @ikudrin. I will hold.

[shchenz]

@ikudrin Hi, I start to commit these NFC changes as now all of them are approved. Welcome your post-commit comment if there is any. Thank you again for your review!

llvm/include/llvm/CodeGen/AsmPrinter.h

public:
 
   /// Emit something like ".long Label + Offset" or ".quad Label + Offset"
   /// depending on the DWARF format.
   void emitDwarfOffset(const MCSymbol *Label, uint64_t Offset) const;
 
   /// Emit 32- or 64-bit value depending on the DWARF format.
   void emitDwarfLengthOrOffset(uint64_t Value) const;
 
-  /// Emit a special value of 0xffffffff if producing 64-bit debugging info.
-  void maybeEmitDwarf64Mark() const;
-
   /// Emit a unit length field. The actual format, DWARF32 or DWARF64, is chosen
   /// according to the settings.
   void emitDwarfUnitLength(uint64_t Length, const Twine &Comment) const;
 
   /// Emit a unit length field. The actual format, DWARF32 or DWARF64, is chosen
   /// according to the settings.
   void emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
                            const Twine &Comment) const;

llvm/include/llvm/MC/MCStreamer.h

public:
   void emitRawText(const Twine &String);
 
   /// Streamer specific finalization.
   virtual void finishImpl();
   /// Finish emission of machine code.
   void Finish(SMLoc EndLoc = SMLoc());
 
   virtual bool mayHaveInstructions(MCSection &Sec) const { return true; }
+
+  /// Emit a special value of 0xffffffff if producing 64-bit debugging info.
+  void maybeEmitDwarf64Mark();
+
+  /// Emit a unit length field. The actual format, DWARF32 or DWARF64, is chosen
+  /// according to the settings.
+  virtual void emitDwarfUnitLength(uint64_t Length, const Twine &Comment);
+
+  /// Emit a unit length field. The actual format, DWARF32 or DWARF64, is chosen
+  /// according to the settings.
+  virtual void emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
+                                   const Twine &Comment);
 };
 
 /// Create a dummy machine code streamer, which does nothing. This is useful for
 /// timing the assembler front end.
 MCStreamer *createNullStreamer(MCContext &Ctx);
 
 } // end namespace llvm
 
 #endif // LLVM_MC_MCSTREAMER_H

llvm/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp

void AsmPrinter::emitDwarfOffset(const MCSymbol *Label, uint64_t Offset) const {
   emitLabelPlusOffset(Label, Offset, getDwarfOffsetByteSize());
 }
 
 void AsmPrinter::emitDwarfLengthOrOffset(uint64_t Value) const {
   assert(isDwarf64() || Value <= UINT32_MAX);
   OutStreamer->emitIntValue(Value, getDwarfOffsetByteSize());
 }
 
-void AsmPrinter::maybeEmitDwarf64Mark() const {
-  if (!isDwarf64())
-    return;
-  OutStreamer->AddComment("DWARF64 Mark");
-  OutStreamer->emitInt32(dwarf::DW_LENGTH_DWARF64);
-}
-
 void AsmPrinter::emitDwarfUnitLength(uint64_t Length,
                                      const Twine &Comment) const {
-  assert(isDwarf64() || Length <= dwarf::DW_LENGTH_lo_reserved);
-  maybeEmitDwarf64Mark();
-  OutStreamer->AddComment(Comment);
-  OutStreamer->emitIntValue(Length, getDwarfOffsetByteSize());
+  OutStreamer->emitDwarfUnitLength(Length, Comment);
 }
 
 void AsmPrinter::emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
                                      const Twine &Comment) const {
-  maybeEmitDwarf64Mark();
-  OutStreamer->AddComment(Comment);
-  OutStreamer->emitAbsoluteSymbolDiff(Hi, Lo, getDwarfOffsetByteSize());
+  OutStreamer->emitDwarfUnitLength(Hi, Lo, Comment);
 }
 
 void AsmPrinter::emitCallSiteOffset(const MCSymbol *Hi, const MCSymbol *Lo,
                                     unsigned Encoding) const {
   // The least significant 3 bits specify the width of the encoding
   if ((Encoding & 0x7) == dwarf::DW_EH_PE_uleb128)
     emitLabelDifferenceAsULEB128(Hi, Lo);
   else

llvm/lib/MC/MCStreamer.cpp

void MCStreamer::Finish(SMLoc EndLoc) {
 
   MCTargetStreamer *TS = getTargetStreamer();
   if (TS)
     TS->finish();
 
   finishImpl();
 }
 
+void MCStreamer::maybeEmitDwarf64Mark() {
+  if (Context.getDwarfFormat() != dwarf::DWARF64)
+    return;
+  AddComment("DWARF64 Mark");
+  emitInt32(dwarf::DW_LENGTH_DWARF64);
+}
+
+void MCStreamer::emitDwarfUnitLength(uint64_t Length, const Twine &Comment) {
+  assert(Context.getDwarfFormat() == dwarf::DWARF64 ||
+         Length <= dwarf::DW_LENGTH_lo_reserved);
+  maybeEmitDwarf64Mark();
+  AddComment(Comment);
+  emitIntValue(Length, dwarf::getDwarfOffsetByteSize(Context.getDwarfFormat()));
+}
+
+void MCStreamer::emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
+                                     const Twine &Comment) {
+  maybeEmitDwarf64Mark();
+  AddComment(Comment);
+  emitAbsoluteSymbolDiff(
+      Hi, Lo, dwarf::getDwarfOffsetByteSize(Context.getDwarfFormat()));
+}
+
 void MCStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
   visitUsedExpr(*Value);
   Symbol->setVariableValue(Value);
 
   MCTargetStreamer *TS = getTargetStreamer();
   if (TS)
     TS->emitAssignment(Symbol, Value);
 }

llvm/unittests/CodeGen/AsmPrinterDwarfTest.cpp

 }
 
 TEST_F(AsmPrinterGetUnitLengthFieldByteSizeTest, DWARF64) {
   if (!init("x86_64-pc-linux", /*DwarfVersion=*/4, dwarf::DWARF64))
     return;
 
   EXPECT_EQ(TestPrinter->getAP()->getUnitLengthFieldByteSize(), 12u);
 }
 
-class AsmPrinterMaybeEmitDwarf64MarkTest : public AsmPrinterFixtureBase {};
-
-TEST_F(AsmPrinterMaybeEmitDwarf64MarkTest, DWARF32) {
-  if (!init("x86_64-pc-linux", /*DwarfVersion=*/4, dwarf::DWARF32))
-    return;
-
-  EXPECT_CALL(TestPrinter->getMS(), emitIntValue(_, _)).Times(0);
-  TestPrinter->getAP()->maybeEmitDwarf64Mark();
-}
-
-TEST_F(AsmPrinterMaybeEmitDwarf64MarkTest, DWARF64) {
-  if (!init("x86_64-pc-linux", /*DwarfVersion=*/4, dwarf::DWARF64))
-    return;
-
-  EXPECT_CALL(TestPrinter->getMS(), emitIntValue(dwarf::DW_LENGTH_DWARF64, 4));
-  TestPrinter->getAP()->maybeEmitDwarf64Mark();
-}
-
 class AsmPrinterEmitDwarfUnitLengthAsIntTest : public AsmPrinterFixtureBase {
 protected:
   uint64_t Val = 42;
 };
 
 TEST_F(AsmPrinterEmitDwarfUnitLengthAsIntTest, DWARF32) {
   if (!init("x86_64-pc-linux", /*DwarfVersion=*/4, dwarf::DWARF32))
     return;