[MC] Remove SectionKind from MCSection (llvm#96067)

There are only three actual uses of the section kind in MCSection:
isText(), XCOFF, and WebAssembly. Store isText() in the MCSection, and
store other info in the actual section variants where required.

ELF and COFF flags also encode all relevant information, so for these
two section variants, remove the SectionKind parameter entirely.

This allows to remove the string switch (which is unnecessary and
inaccurate) from createELFSectionImpl. This was introduced in
[D133456](https://reviews.llvm.org/D133456), but apparently, it was
never hit for non-writable sections anyway and the resulting kind was
never used.

Author: aengelke

llvm/include/llvm/MC/MCContext.h

@@ -357,8 +357,7 @@ class MCContext {
                                               unsigned Instance);
 
   MCSectionELF *createELFSectionImpl(StringRef Section, unsigned Type,
-                                     unsigned Flags, SectionKind K,
-                                     unsigned EntrySize,
+                                     unsigned Flags, unsigned EntrySize,
                                      const MCSymbolELF *Group, bool IsComdat,
                                      unsigned UniqueID,
                                      const MCSymbolELF *LinkedToSym);
@@ -602,13 +601,11 @@ class MCContext {
                                 MCSection *Parent, const MCExpr *SubsectionId);
 
   MCSectionCOFF *getCOFFSection(StringRef Section, unsigned Characteristics,
-                                SectionKind Kind, StringRef COMDATSymName,
-                                int Selection,
+                                StringRef COMDATSymName, int Selection,
                                 unsigned UniqueID = GenericSectionID,
                                 const char *BeginSymName = nullptr);
 
   MCSectionCOFF *getCOFFSection(StringRef Section, unsigned Characteristics,
-                                SectionKind Kind,
                                 const char *BeginSymName = nullptr);
 
   /// Gets or creates a section equivalent to Sec that is associated with the

llvm/include/llvm/MC/MCSection.h

@@ -104,6 +104,8 @@ class MCSection {
 
   bool IsRegistered : 1;
 
+  bool IsText : 1;
+
   MCDummyFragment DummyFragment;
 
   // Mapping from subsection number to fragment list. At layout time, the
@@ -124,17 +126,16 @@ class MCSection {
   // TODO Make Name private when possible.
   StringRef Name;
   SectionVariant Variant;
-  SectionKind Kind;
 
-  MCSection(SectionVariant V, StringRef Name, SectionKind K, MCSymbol *Begin);
+  MCSection(SectionVariant V, StringRef Name, bool IsText, MCSymbol *Begin);
   ~MCSection();
 
 public:
   MCSection(const MCSection &) = delete;
   MCSection &operator=(const MCSection &) = delete;
 
   StringRef getName() const { return Name; }
-  SectionKind getKind() const { return Kind; }
+  bool isText() const { return IsText; }
 
   SectionVariant getVariant() const { return Variant; }
 

llvm/include/llvm/MC/MCSectionCOFF.h

@@ -14,6 +14,7 @@
 #define LLVM_MC_MCSECTIONCOFF_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/BinaryFormat/COFF.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/SectionKind.h"
 #include <cassert>
@@ -50,10 +51,11 @@ class MCSectionCOFF final : public MCSection {
   friend class MCContext;
   // The storage of Name is owned by MCContext's COFFUniquingMap.
   MCSectionCOFF(StringRef Name, unsigned Characteristics,
-                MCSymbol *COMDATSymbol, int Selection, SectionKind K,
-                MCSymbol *Begin)
-      : MCSection(SV_COFF, Name, K, Begin), Characteristics(Characteristics),
-        COMDATSymbol(COMDATSymbol), Selection(Selection) {
+                MCSymbol *COMDATSymbol, int Selection, MCSymbol *Begin)
+      : MCSection(SV_COFF, Name, Characteristics & COFF::IMAGE_SCN_CNT_CODE,
+                  Begin),
+        Characteristics(Characteristics), COMDATSymbol(COMDATSymbol),
+        Selection(Selection) {
     assert((Characteristics & 0x00F00000) == 0 &&
            "alignment must not be set upon section creation");
   }

llvm/include/llvm/MC/MCSectionDXContainer.h

@@ -24,7 +24,7 @@ class MCSectionDXContainer final : public MCSection {
   friend class MCContext;
 
   MCSectionDXContainer(StringRef Name, SectionKind K, MCSymbol *Begin)
-      : MCSection(SV_DXContainer, Name, K, Begin) {}
+      : MCSection(SV_DXContainer, Name, K.isText(), Begin) {}
 
 public:
   void printSwitchToSection(const MCAsmInfo &, const Triple &, raw_ostream &,

llvm/include/llvm/MC/MCSectionELF.h

@@ -15,6 +15,7 @@
 
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/BinaryFormat/ELF.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/SectionKind.h"
@@ -49,13 +50,13 @@ class MCSectionELF final : public MCSection {
   friend class MCContext;
 
   // The storage of Name is owned by MCContext's ELFUniquingMap.
-  MCSectionELF(StringRef Name, unsigned type, unsigned flags, SectionKind K,
+  MCSectionELF(StringRef Name, unsigned type, unsigned flags,
                unsigned entrySize, const MCSymbolELF *group, bool IsComdat,
                unsigned UniqueID, MCSymbol *Begin,
                const MCSymbolELF *LinkedToSym)
-      : MCSection(SV_ELF, Name, K, Begin), Type(type), Flags(flags),
-        UniqueID(UniqueID), EntrySize(entrySize), Group(group, IsComdat),
-        LinkedToSym(LinkedToSym) {
+      : MCSection(SV_ELF, Name, flags & ELF::SHF_EXECINSTR, Begin), Type(type),
+        Flags(flags), UniqueID(UniqueID), EntrySize(entrySize),
+        Group(group, IsComdat), LinkedToSym(LinkedToSym) {
     if (Group.getPointer())
       Group.getPointer()->setIsSignature();
   }

llvm/include/llvm/MC/MCSectionGOFF.h

@@ -30,7 +30,8 @@ class MCSectionGOFF final : public MCSection {
 
   friend class MCContext;
   MCSectionGOFF(StringRef Name, SectionKind K, MCSection *P, const MCExpr *Sub)
-      : MCSection(SV_GOFF, Name, K, nullptr), Parent(P), SubsectionId(Sub) {}
+      : MCSection(SV_GOFF, Name, K.isText(), nullptr), Parent(P),
+        SubsectionId(Sub) {}
 
 public:
   void printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,

llvm/include/llvm/MC/MCSectionSPIRV.h

@@ -23,8 +23,8 @@ class MCSymbol;
 class MCSectionSPIRV final : public MCSection {
   friend class MCContext;
 
-  MCSectionSPIRV(SectionKind K, MCSymbol *Begin)
-      : MCSection(SV_SPIRV, "", K, Begin) {}
+  MCSectionSPIRV()
+      : MCSection(SV_SPIRV, "", /*IsText=*/true, /*Begin=*/nullptr) {}
   // TODO: Add StringRef Name to MCSectionSPIRV.
 
 public:

llvm/include/llvm/MC/MCSectionWasm.h

@@ -40,15 +40,20 @@ class MCSectionWasm final : public MCSection {
   // For data sections, whether to use a passive segment
   bool IsPassive = false;
 
+  bool IsWasmData;
+
+  bool IsMetadata;
+
   // For data sections, bitfield of WasmSegmentFlag
   unsigned SegmentFlags;
 
   // The storage of Name is owned by MCContext's WasmUniquingMap.
   friend class MCContext;
   MCSectionWasm(StringRef Name, SectionKind K, unsigned SegmentFlags,
                 const MCSymbolWasm *Group, unsigned UniqueID, MCSymbol *Begin)
-      : MCSection(SV_Wasm, Name, K, Begin), UniqueID(UniqueID), Group(Group),
-        SegmentFlags(SegmentFlags) {}
+      : MCSection(SV_Wasm, Name, K.isText(), Begin), UniqueID(UniqueID),
+        Group(Group), IsWasmData(K.isReadOnly() || K.isWriteable()),
+        IsMetadata(K.isMetadata()), SegmentFlags(SegmentFlags) {}
 
 public:
   /// Decides whether a '.section' directive should be printed before the
@@ -64,10 +69,8 @@ class MCSectionWasm final : public MCSection {
   bool useCodeAlign() const override;
   bool isVirtualSection() const override;
 
-  bool isWasmData() const {
-    return Kind.isGlobalWriteableData() || Kind.isReadOnly() ||
-           Kind.isThreadLocal();
-  }
+  bool isWasmData() const { return IsWasmData; }
+  bool isMetadata() const { return IsMetadata; }
 
   bool isUnique() const { return UniqueID != ~0U; }
   unsigned getUniqueID() const { return UniqueID; }

llvm/include/llvm/MC/MCSectionXCOFF.h

@@ -37,17 +37,18 @@ class MCSectionXCOFF final : public MCSection {
   StringRef SymbolTableName;
   std::optional<XCOFF::DwarfSectionSubtypeFlags> DwarfSubtypeFlags;
   bool MultiSymbolsAllowed;
+  SectionKind Kind;
   static constexpr unsigned DefaultAlignVal = 4;
   static constexpr unsigned DefaultTextAlignVal = 32;
 
   MCSectionXCOFF(StringRef Name, XCOFF::StorageMappingClass SMC,
                  XCOFF::SymbolType ST, SectionKind K, MCSymbolXCOFF *QualName,
                  MCSymbol *Begin, StringRef SymbolTableName,
                  bool MultiSymbolsAllowed)
-      : MCSection(SV_XCOFF, Name, K, Begin),
+      : MCSection(SV_XCOFF, Name, K.isText(), Begin),
         CsectProp(XCOFF::CsectProperties(SMC, ST)), QualName(QualName),
         SymbolTableName(SymbolTableName), DwarfSubtypeFlags(std::nullopt),
-        MultiSymbolsAllowed(MultiSymbolsAllowed) {
+        MultiSymbolsAllowed(MultiSymbolsAllowed), Kind(K) {
     assert(
         (ST == XCOFF::XTY_SD || ST == XCOFF::XTY_CM || ST == XCOFF::XTY_ER) &&
         "Invalid or unhandled type for csect.");
@@ -72,9 +73,9 @@ class MCSectionXCOFF final : public MCSection {
                  XCOFF::DwarfSectionSubtypeFlags DwarfSubtypeFlags,
                  MCSymbol *Begin, StringRef SymbolTableName,
                  bool MultiSymbolsAllowed)
-      : MCSection(SV_XCOFF, Name, K, Begin), QualName(QualName),
+      : MCSection(SV_XCOFF, Name, K.isText(), Begin), QualName(QualName),
         SymbolTableName(SymbolTableName), DwarfSubtypeFlags(DwarfSubtypeFlags),
-        MultiSymbolsAllowed(MultiSymbolsAllowed) {
+        MultiSymbolsAllowed(MultiSymbolsAllowed), Kind(K) {
     assert(QualName != nullptr && "QualName is needed.");
 
     // FIXME: use a more meaningful name for non csect sections.
@@ -125,6 +126,7 @@ class MCSectionXCOFF final : public MCSection {
   std::optional<XCOFF::CsectProperties> getCsectProp() const {
     return CsectProp;
   }
+  SectionKind getKind() const { return Kind; }
 };
 
 } // end namespace llvm

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -2415,8 +2415,7 @@ bool AsmPrinter::doFinalization(Module &M) {
             SectionName,
             COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ |
                 COFF::IMAGE_SCN_LNK_COMDAT,
-            SectionKind::getReadOnly(), Stub.first->getName(),
-            COFF::IMAGE_COMDAT_SELECT_ANY));
+            Stub.first->getName(), COFF::IMAGE_COMDAT_SELECT_ANY));
         emitAlignment(Align(DL.getPointerSize()));
         OutStreamer->emitSymbolAttribute(Stub.first, MCSA_Global);
         OutStreamer->emitLabel(Stub.first);
@@ -2898,8 +2897,8 @@ bool AsmPrinter::emitSpecialLLVMGlobal(const GlobalVariable *GV) {
     // For ARM64EC, print the table that maps between symbols and the
     // corresponding thunks to translate between x64 and AArch64 code.
     // This table is generated by AArch64Arm64ECCallLowering.
-    OutStreamer->switchSection(OutContext.getCOFFSection(
-        ".hybmp$x", COFF::IMAGE_SCN_LNK_INFO, SectionKind::getMetadata()));
+    OutStreamer->switchSection(
+        OutContext.getCOFFSection(".hybmp$x", COFF::IMAGE_SCN_LNK_INFO));
     auto *Arr = cast<ConstantArray>(GV->getInitializer());
     for (auto &U : Arr->operands()) {
       auto *C = cast<Constant>(U);
@@ -3158,7 +3157,7 @@ void AsmPrinter::emitAlignment(Align Alignment, const GlobalObject *GV,
   if (Alignment == Align(1))
     return; // 1-byte aligned: no need to emit alignment.
 
-  if (getCurrentSection()->getKind().isText()) {
+  if (getCurrentSection()->isText()) {
     const MCSubtargetInfo *STI = nullptr;
     if (this->MF)
       STI = &getSubtargetInfo();