[MC][AArch64][ARM][X86] Push target-dependent assembler flags into targets (#139844)

The .syntax unified directive and .codeX/.code X directives are, other
than some simple common printing code, exclusively implemented in the
targets themselves. Thus, remove the corresponding MCAF_* flags and
reimplement the directives solely within the targets. This avoids
exposing all targets to all other targets' flags.

Since MCAF_SubsectionsViaSymbols is all that remains, convert it to its
own function like other directives, simplifying its implementation.

Note that, on X86, we now always need a target streamer when parsing
assembly, as it's now used for directives that aren't COFF-specific. It
still does not however need to do anything when producing a non-COFF
object file, so this commit does not introduce any new target streamers.

There is some churn in test output, and corresponding UTC regex changes,
due to comments no longer being flushed by these various directives (and
EmitEOL is not exposed outside MCAsmStreamer.cpp so we couldn't do so
even if we wanted to), but that was a bit odd to be doing anyway.

This is motivated by Morello LLVM, which adds yet another assembler flag
to distinguish A64 and C64 instruction sets, but did not update every
switch and so emits warnings during the build. Rather than fix those
warnings it seems better to instead make the problem not exist in the
first place via this change.

Author: jrtc27

llvm/include/llvm/MC/MCAsmBackend.h

@@ -213,9 +213,6 @@ class MCAsmBackend {
   /// Give backend an opportunity to finish layout after relaxation
   virtual void finishLayout(MCAssembler const &Asm) const {}
 
-  /// Handle any target-specific assembler flags. By default, do nothing.
-  virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
-
   /// Generate the compact unwind encoding for the CFI instructions.
   virtual uint64_t generateCompactUnwindEncoding(const MCDwarfFrameInfo *FI,
                                                  const MCContext *Ctxt) const {

llvm/include/llvm/MC/MCAsmInfo.h

@@ -166,13 +166,6 @@ class MCAsmInfo {
   const char *InlineAsmStart;
   const char *InlineAsmEnd;
 
-  /// These are assembly directives that tells the assembler to interpret the
-  /// following instructions differently.  Defaults to ".code16", ".code32",
-  /// ".code64".
-  const char *Code16Directive;
-  const char *Code32Directive;
-  const char *Code64Directive;
-
   /// Which dialect of an assembler variant to use.  Defaults to 0
   unsigned AssemblerDialect = 0;
 
@@ -544,9 +537,6 @@ class MCAsmInfo {
 
   const char *getInlineAsmStart() const { return InlineAsmStart; }
   const char *getInlineAsmEnd() const { return InlineAsmEnd; }
-  const char *getCode16Directive() const { return Code16Directive; }
-  const char *getCode32Directive() const { return Code32Directive; }
-  const char *getCode64Directive() const { return Code64Directive; }
   unsigned getAssemblerDialect() const { return AssemblerDialect; }
   bool doesAllowAtInName() const { return AllowAtInName; }
   void setAllowAtInName(bool V) { AllowAtInName = V; }

llvm/include/llvm/MC/MCDirectives.h

@@ -50,14 +50,6 @@ enum MCSymbolAttr {
   MCSA_Memtag,                  ///< .memtag (ELF)
 };
 
-enum MCAssemblerFlag {
-  MCAF_SyntaxUnified,         ///< .syntax (ARM/ELF)
-  MCAF_SubsectionsViaSymbols, ///< .subsections_via_symbols (MachO)
-  MCAF_Code16,                ///< .code16 (X86) / .code 16 (ARM)
-  MCAF_Code32,                ///< .code32 (X86) / .code 32 (ARM)
-  MCAF_Code64                 ///< .code64 (X86)
-};
-
 enum MCDataRegionType {
   MCDR_DataRegion,            ///< .data_region
   MCDR_DataRegionJT8,         ///< .data_region jt8

llvm/include/llvm/MC/MCELFStreamer.h

@@ -53,7 +53,6 @@ class MCELFStreamer : public MCObjectStreamer {
   void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
   void emitLabelAtPos(MCSymbol *Symbol, SMLoc Loc, MCDataFragment &F,
                       uint64_t Offset) override;
-  void emitAssemblerFlag(MCAssemblerFlag Flag) override;
   void emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) override;
   bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
   void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,

llvm/include/llvm/MC/MCStreamer.h

@@ -169,6 +169,11 @@ class ARMTargetStreamer : public MCTargetStreamer {
 
   virtual void annotateTLSDescriptorSequence(const MCSymbolRefExpr *SRE);
 
+  virtual void emitSyntaxUnified();
+
+  virtual void emitCode16();
+  virtual void emitCode32();
+
   // Note in the output that the specified \p Symbol is a Thumb mode function.
   virtual void emitThumbFunc(MCSymbol *Symbol);
   virtual void emitThumbSet(MCSymbol *Symbol, const MCExpr *Value);
@@ -471,8 +476,8 @@ class MCStreamer {
 
   virtual void emitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol);
 
-  /// Note in the output the specified \p Flag.
-  virtual void emitAssemblerFlag(MCAssemblerFlag Flag);
+  /// Emit a .subsection_via_symbols directive.
+  virtual void emitSubsectionsViaSymbols();
 
   /// Emit the given list \p Options of strings as linker
   /// options into the output.

llvm/include/llvm/MC/MCWasmStreamer.h

@@ -44,7 +44,6 @@ class MCWasmStreamer : public MCObjectStreamer {
   void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
   void emitLabelAtPos(MCSymbol *Symbol, SMLoc Loc, MCDataFragment &F,
                       uint64_t Offset) override;
-  void emitAssemblerFlag(MCAssemblerFlag Flag) override;
   void emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) override;
   bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
   void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,

llvm/include/llvm/MC/MCWinCOFFStreamer.h

@@ -45,7 +45,6 @@ class MCWinCOFFStreamer : public MCObjectStreamer {
   void initSections(bool NoExecStack, const MCSubtargetInfo &STI) override;
   void changeSection(MCSection *Section, uint32_t Subsection = 0) override;
   void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
-  void emitAssemblerFlag(MCAssemblerFlag Flag) override;
   bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
   void emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
   void beginCOFFSymbolDef(MCSymbol const *Symbol) override;

llvm/lib/MC/MCAsmInfo.cpp

@@ -48,9 +48,6 @@ MCAsmInfo::MCAsmInfo() {
   LinkerPrivateGlobalPrefix = "";
   InlineAsmStart = "APP";
   InlineAsmEnd = "NO_APP";
-  Code16Directive = ".code16";
-  Code32Directive = ".code32";
-  Code64Directive = ".code64";
   ZeroDirective = "\t.zero\t";
   AsciiDirective = "\t.ascii\t";
   AscizDirective = "\t.asciz\t";

llvm/lib/MC/MCAsmStreamer.cpp

@@ -182,7 +182,7 @@ class MCAsmStreamer final : public MCStreamer {
 
   void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
 
-  void emitAssemblerFlag(MCAssemblerFlag Flag) override;
+  void emitSubsectionsViaSymbols() override;
   void emitLinkerOptions(ArrayRef<std::string> Options) override;
   void emitDataRegion(MCDataRegionType Kind) override;
   void emitVersionMin(MCVersionMinType Kind, unsigned Major, unsigned Minor,
@@ -597,15 +597,8 @@ void MCAsmStreamer::emitGNUAttribute(unsigned Tag, unsigned Value) {
   OS << "\t.gnu_attribute " << Tag << ", " << Value << "\n";
 }
 
-void MCAsmStreamer::emitAssemblerFlag(MCAssemblerFlag Flag) {
-  switch (Flag) {
-  case MCAF_SyntaxUnified:         OS << "\t.syntax unified"; break;
-  case MCAF_SubsectionsViaSymbols: OS << ".subsections_via_symbols"; break;
-  case MCAF_Code16:                OS << '\t'<< MAI->getCode16Directive();break;
-  case MCAF_Code32:                OS << '\t'<< MAI->getCode32Directive();break;
-  case MCAF_Code64:                OS << '\t'<< MAI->getCode64Directive();break;
-  }
-  EmitEOL();
+void MCAsmStreamer::emitSubsectionsViaSymbols() {
+  OS << ".subsections_via_symbols\n";
 }
 
 void MCAsmStreamer::emitLinkerOptions(ArrayRef<std::string> Options) {

llvm/lib/MC/MCELFStreamer.cpp

@@ -84,11 +84,6 @@ void MCELFStreamer::emitLabelAtPos(MCSymbol *S, SMLoc Loc, MCDataFragment &F,
     Symbol->setType(ELF::STT_TLS);
 }
 
-void MCELFStreamer::emitAssemblerFlag(MCAssemblerFlag Flag) {
-  // Let the target do whatever target specific stuff it needs to do.
-  getAssembler().getBackend().handleAssemblerFlag(Flag);
-}
-
 // If bundle alignment is used and there are any instructions in the section, it
 // needs to be aligned to at least the bundle size.
 static void setSectionAlignmentForBundling(const MCAssembler &Assembler,