[NFC] Refactor how CFI section types are represented in AsmPrinter

In terms of readability, the `enum CFIMoveType` didn't better document what it
intends to convey i.e. the type of CFI section that gets emitted.

Reviewed By: dblaikie, MaskRay

Differential Revision: https://reviews.llvm.org/D76519

llvm/include/llvm/CodeGen/AsmPrinter.h

@@ -157,6 +157,13 @@ public:
           TimerGroupDescription(TimerGroupDescription) {}
   };
 
+  // Flags representing which CFI section is required for a function/module.
+  enum class CFISection : unsigned {
+    None = 0, ///< Do not emit either .eh_frame or .debug_frame
+    EH = 1,   ///< Emit .eh_frame
+    Debug = 2 ///< Emit .debug_frame
+  };
+
 private:
   MCSymbol *CurrentFnEnd = nullptr;
 
@@ -199,8 +206,8 @@ private:
   /// context.
   PseudoProbeHandler *PP = nullptr;
 
-  /// If the current module uses dwarf CFI annotations strictly for debugging.
-  bool isCFIMoveForDebugging = false;
+  /// CFISection type the module needs i.e. either .eh_frame or .debug_frame.
+  CFISection ModuleCFISection = CFISection::None;
 
 protected:
   explicit AsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer);
@@ -357,12 +364,14 @@ public:
 
   void emitRemarksSection(remarks::RemarkStreamer &RS);
 
-  enum CFIMoveType { CFI_M_None, CFI_M_EH, CFI_M_Debug };
-  CFIMoveType needsCFIMoves() const;
+  /// Get the CFISection type for a function.
+  CFISection getFunctionCFISectionType(const Function &F) const;
 
-  /// Returns false if needsCFIMoves() == CFI_M_EH for any function
-  /// in the module.
-  bool needsOnlyDebugCFIMoves() const { return isCFIMoveForDebugging; }
+  /// Get the CFISection type for a function.
+  CFISection getFunctionCFISectionType(const MachineFunction &MF) const;
+
+  /// Get the CFISection type for the module.
+  CFISection getModuleCFISectionType() const { return ModuleCFISection; }
 
   bool needsSEHMoves();
 

llvm/lib/CodeGen/AsmPrinter/ARMException.cpp

@@ -39,13 +39,13 @@ void ARMException::beginFunction(const MachineFunction *MF) {
   if (Asm->MAI->getExceptionHandlingType() == ExceptionHandling::ARM)
     getTargetStreamer().emitFnStart();
   // See if we need call frame info.
-  AsmPrinter::CFIMoveType MoveType = Asm->needsCFIMoves();
-  assert(MoveType != AsmPrinter::CFI_M_EH &&
+  AsmPrinter::CFISection CFISecType = Asm->getFunctionCFISectionType(*MF);
+  assert(CFISecType != AsmPrinter::CFISection::EH &&
          "non-EH CFI not yet supported in prologue with EHABI lowering");
 
-  if (MoveType == AsmPrinter::CFI_M_Debug) {
+  if (CFISecType == AsmPrinter::CFISection::Debug) {
     if (!hasEmittedCFISections) {
-      if (Asm->needsOnlyDebugCFIMoves())
+      if (Asm->getModuleCFISectionType() == AsmPrinter::CFISection::Debug)
         Asm->OutStreamer->emitCFISections(false, true);
       hasEmittedCFISections = true;
     }

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -351,21 +351,18 @@ bool AsmPrinter::doInitialization(Module &M) {
   case ExceptionHandling::SjLj:
   case ExceptionHandling::DwarfCFI:
   case ExceptionHandling::ARM:
-    isCFIMoveForDebugging = true;
-    if (MAI->getExceptionHandlingType() != ExceptionHandling::DwarfCFI)
-      break;
-    for (auto &F: M.getFunctionList()) {
-      // If the module contains any function with unwind data,
-      // .eh_frame has to be emitted.
-      // Ignore functions that won't get emitted.
-      if (!F.isDeclarationForLinker() && F.needsUnwindTableEntry()) {
-        isCFIMoveForDebugging = false;
+    for (auto &F : M.getFunctionList()) {
+      // If any function needsUnwindTableEntry(), it needs .eh_frame and hence
+      // the module needs .eh_frame. If we have found that case, we are done.
+      if (ModuleCFISection == AsmPrinter::CFISection::EH)
         break;
-      }
+      if (ModuleCFISection == AsmPrinter::CFISection::None)
+        ModuleCFISection = getFunctionCFISectionType(F);
     }
+    assert(MAI->getExceptionHandlingType() == ExceptionHandling::DwarfCFI ||
+           ModuleCFISection != AsmPrinter::CFISection::EH);
     break;
   default:
-    isCFIMoveForDebugging = false;
     break;
   }
 
@@ -1037,15 +1034,25 @@ static bool emitDebugLabelComment(const MachineInstr *MI, AsmPrinter &AP) {
   return true;
 }
 
-AsmPrinter::CFIMoveType AsmPrinter::needsCFIMoves() const {
+AsmPrinter::CFISection
+AsmPrinter::getFunctionCFISectionType(const Function &F) const {
+  // Ignore functions that won't get emitted.
+  if (F.isDeclarationForLinker())
+    return CFISection::None;
+
   if (MAI->getExceptionHandlingType() == ExceptionHandling::DwarfCFI &&
-      MF->getFunction().needsUnwindTableEntry())
-    return CFI_M_EH;
+      F.needsUnwindTableEntry())
+    return CFISection::EH;
 
-  if (MMI->hasDebugInfo() || MF->getTarget().Options.ForceDwarfFrameSection)
-    return CFI_M_Debug;
+  if (MMI->hasDebugInfo() || TM.Options.ForceDwarfFrameSection)
+    return CFISection::Debug;
 
-  return CFI_M_None;
+  return CFISection::None;
+}
+
+AsmPrinter::CFISection
+AsmPrinter::getFunctionCFISectionType(const MachineFunction &MF) const {
+  return getFunctionCFISectionType(MF.getFunction());
 }
 
 bool AsmPrinter::needsSEHMoves() {
@@ -1058,7 +1065,7 @@ void AsmPrinter::emitCFIInstruction(const MachineInstr &MI) {
       ExceptionHandlingType != ExceptionHandling::ARM)
     return;
 
-  if (needsCFIMoves() == CFI_M_None)
+  if (getFunctionCFISectionType(*MF) == AsmPrinter::CFISection::None)
     return;
 
   // If there is no "real" instruction following this CFI instruction, skip

llvm/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp

@@ -93,9 +93,8 @@ void DwarfCFIException::beginFunction(const MachineFunction *MF) {
   bool hasLandingPads = !MF->getLandingPads().empty();
 
   // See if we need frame move info.
-  AsmPrinter::CFIMoveType MoveType = Asm->needsCFIMoves();
-
-  bool shouldEmitMoves = MoveType != AsmPrinter::CFI_M_None;
+  bool shouldEmitMoves =
+      Asm->getFunctionCFISectionType(*MF) != AsmPrinter::CFISection::None;
 
   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
   unsigned PerEncoding = TLOF.getPersonalityEncoding();
@@ -132,10 +131,14 @@ void DwarfCFIException::beginFragment(const MachineBasicBlock *MBB,
     return;
 
   if (!hasEmittedCFISections) {
-    if (Asm->needsOnlyDebugCFIMoves())
-      Asm->OutStreamer->emitCFISections(false, true);
-    else if (Asm->TM.Options.ForceDwarfFrameSection)
-      Asm->OutStreamer->emitCFISections(true, true);
+    AsmPrinter::CFISection CFISecType = Asm->getModuleCFISectionType();
+    // If we don't say anything it implies `.cfi_sections .eh_frame`, so we
+    // chose not to be verbose in that case. And with `ForceDwarfFrameSection`,
+    // we should always emit .debug_frame.
+    if (CFISecType == AsmPrinter::CFISection::Debug ||
+        Asm->TM.Options.ForceDwarfFrameSection)
+      Asm->OutStreamer->emitCFISections(
+          CFISecType == AsmPrinter::CFISection::EH, true);
     hasEmittedCFISections = true;
   }
 

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -1229,7 +1229,7 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
           ExceptionHandlingType != ExceptionHandling::ARM)
         return;
 
-      if (needsCFIMoves() == CFI_M_None)
+      if (getFunctionCFISectionType(*MF) == CFISection::None)
         return;
 
       OutStreamer->emitCFIBKeyFrame();