[AsmPrinter] Reduce AsmPrinterHandlers virt. fn calls (#96785)

Currently, an AsmPrinterHandler has several methods that allow to
dynamically hook in unwind or debug info emission, e.g. at begin/end of
every function or instruction. The class hierarchy and the actually
overridden functions are as follows:

    (SymSz=setSymbolSize, mFE=markFunctionEnd, BBS=BasicBlockSection,
     FL=Funclet; b=beginX, e=endX)
                          SymSz   Mod Fn  mFE BBS FL  Inst
    AsmPrinterHandler     -       -   -   -   -   -   -
    ` PseudoProbeHandler  -       -   -   -   -   -   -
    ` WinCFGuard          -       e   e   -   -   -   -
    ` EHStreamer          -       -   -   -   -   -   -
      ` DwarfCFIException -       e   be  -   be  -   -
      ` ARMException      -       -   be  e   -   -   -
      ` AIXException      -       -   e   -   -   -   -
      ` WinException      -       e   be  e   -   be  -
      ` WasmException     -       e   be  -   -   -   -
    ` DebugHandlerBase    -       b   be  -   be  -   be
      ` BTFDebug          -       e   -   -   -   -   b
      ` CodeViewDebug     -       be  -   -   -   -   b
      ` DWARFDebug        yes     be  -   -   -   -   b

Doing virtual function calls per instruction is costly and useless when
the called function does nothing.

This commit performs the following clean-up/improvements:

- PseudoProbeHandler is no longer an AsmPrinterHandler -- it used
nothing of its functionality to hook in at the possible points. This
avoids virtual function calls when a pseudo probe printer is present.

- DebugHandlerBase is no longer an AsmPrinterHandler, but a separate
base class. DebugHandlerBase is the only remaining "hook" for begin/end
instruction and setSymbolSize (only used by DWARFDebug). begin/end for
function and basic block sections are never overriden and therefore are
no longer virtual. (Originally I intended there to be only one debug
handler, but BPF as the only target supports two at the same time: DWARF
and BTF.)

- AsmPrinterHandler no longer has begin/end instruction and
setSymbolSize hooks -- these were only used by DebugHandlerBase. This
avoid iterating over handlers in every instruction.

    AsmPrinterHandler     Mod Fn  mFE BBS FL
    ` WinCFGuard          e   e   -   -   -
    ` EHStreamer          -   -   -   -   -
      ` DwarfCFIException e   be  -   be  -
      ` ARMException      -   be  e   -   -
      ` AIXException      -   e   -   -   -
      ` WinException      e   be  e   -   be
      ` WasmException     e   be  -   -   -

                          SymSz   Mod Fn  BBS Inst
    DebugHandlerBase      -       b   be  be  be
    ` BTFDebug            -       e           b
    ` CodeViewDebug       -       be          b
    ` DWARFDebug          yes     be          b

    PseudoProbeHandler (no shared methods)

To continue allowing external users (e.g., Julia) to hook in at every
instruction, a new method addDebugHandler is exposed.

This results in a performance improvement, especially in the -O0 -g0
case with unwind information (e.g., JIT baseline).

Author: aengelke

llvm/include/llvm/CodeGen/AsmPrinter.h

@@ -20,6 +20,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/CodeGen/AsmPrinterHandler.h"
+#include "llvm/CodeGen/DebugHandlerBase.h"
 #include "llvm/CodeGen/DwarfStringPoolEntry.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/StackMaps.h"
@@ -145,14 +146,14 @@ class AsmPrinter : public MachineFunctionPass {
 
   /// struct HandlerInfo and Handlers permit users or target extended
   /// AsmPrinter to add their own handlers.
-  struct HandlerInfo {
-    std::unique_ptr<AsmPrinterHandler> Handler;
+  template <class H> struct HandlerInfo {
+    std::unique_ptr<H> Handler;
     StringRef TimerName;
     StringRef TimerDescription;
     StringRef TimerGroupName;
     StringRef TimerGroupDescription;
 
-    HandlerInfo(std::unique_ptr<AsmPrinterHandler> Handler, StringRef TimerName,
+    HandlerInfo(std::unique_ptr<H> Handler, StringRef TimerName,
                 StringRef TimerDescription, StringRef TimerGroupName,
                 StringRef TimerGroupDescription)
         : Handler(std::move(Handler)), TimerName(TimerName),
@@ -205,9 +206,13 @@ class AsmPrinter : public MachineFunctionPass {
 
   /// A vector of all debug/EH info emitters we should use. This vector
   /// maintains ownership of the emitters.
-  std::vector<HandlerInfo> Handlers;
+  SmallVector<HandlerInfo<AsmPrinterHandler>, 2> Handlers;
   size_t NumUserHandlers = 0;
 
+  /// Debuginfo handler. Protected so that targets can add their own.
+  SmallVector<HandlerInfo<DebugHandlerBase>, 1> DebugHandlers;
+  size_t NumUserDebugHandlers = 0;
+
   StackMaps SM;
 
 private:
@@ -222,7 +227,7 @@ class AsmPrinter : public MachineFunctionPass {
 
   /// A handler that supports pseudo probe emission with embedded inline
   /// context.
-  PseudoProbeHandler *PP = nullptr;
+  std::unique_ptr<PseudoProbeHandler> PP;
 
   /// CFISection type the module needs i.e. either .eh_frame or .debug_frame.
   CFISection ModuleCFISection = CFISection::None;
@@ -531,11 +536,16 @@ class AsmPrinter : public MachineFunctionPass {
   // Overridable Hooks
   //===------------------------------------------------------------------===//
 
-  void addAsmPrinterHandler(HandlerInfo Handler) {
+  void addAsmPrinterHandler(HandlerInfo<AsmPrinterHandler> Handler) {
     Handlers.insert(Handlers.begin(), std::move(Handler));
     NumUserHandlers++;
   }
 
+  void addDebugHandler(HandlerInfo<DebugHandlerBase> Handler) {
+    DebugHandlers.insert(DebugHandlers.begin(), std::move(Handler));
+    NumUserDebugHandlers++;
+  }
+
   // Targets can, or in the case of EmitInstruction, must implement these to
   // customize output.
 

llvm/include/llvm/CodeGen/AsmPrinterHandler.h

@@ -34,10 +34,6 @@ class AsmPrinterHandler {
 public:
   virtual ~AsmPrinterHandler();
 
-  /// For symbols that have a size designated (e.g. common symbols),
-  /// this tracks that size.
-  virtual void setSymbolSize(const MCSymbol *Sym, uint64_t Size) = 0;
-
   virtual void beginModule(Module *M) {}
 
   /// Emit all sections that should come after the content.
@@ -72,12 +68,6 @@ class AsmPrinterHandler {
   virtual void beginFunclet(const MachineBasicBlock &MBB,
                             MCSymbol *Sym = nullptr) {}
   virtual void endFunclet() {}
-
-  /// Process beginning of an instruction.
-  virtual void beginInstruction(const MachineInstr *MI) = 0;
-
-  /// Process end of an instruction.
-  virtual void endInstruction() = 0;
 };
 
 } // End of namespace llvm

llvm/include/llvm/CodeGen/DebugHandlerBase.h

@@ -50,10 +50,14 @@ struct DbgVariableLocation {
 
 /// Base class for debug information backends. Common functionality related to
 /// tracking which variables and scopes are alive at a given PC live here.
-class DebugHandlerBase : public AsmPrinterHandler {
+class DebugHandlerBase {
 protected:
   DebugHandlerBase(AsmPrinter *A);
 
+public:
+  virtual ~DebugHandlerBase();
+
+protected:
   /// Target of debug info emission.
   AsmPrinter *Asm = nullptr;
 
@@ -116,18 +120,22 @@ class DebugHandlerBase : public AsmPrinterHandler {
 private:
   InstructionOrdering InstOrdering;
 
-  // AsmPrinterHandler overrides.
 public:
-  void beginModule(Module *M) override;
+  /// For symbols that have a size designated (e.g. common symbols),
+  /// this tracks that size. Only used by DWARF.
+  virtual void setSymbolSize(const MCSymbol *Sym, uint64_t Size) {}
+
+  virtual void beginModule(Module *M);
+  virtual void endModule() = 0;
 
-  void beginInstruction(const MachineInstr *MI) override;
-  void endInstruction() override;
+  virtual void beginInstruction(const MachineInstr *MI);
+  virtual void endInstruction();
 
-  void beginFunction(const MachineFunction *MF) override;
-  void endFunction(const MachineFunction *MF) override;
+  void beginFunction(const MachineFunction *MF);
+  void endFunction(const MachineFunction *MF);
 
-  void beginBasicBlockSection(const MachineBasicBlock &MBB) override;
-  void endBasicBlockSection(const MachineBasicBlock &MBB) override;
+  void beginBasicBlockSection(const MachineBasicBlock &MBB);
+  void endBasicBlockSection(const MachineBasicBlock &MBB);
 
   /// Return Label preceding the instruction.
   MCSymbol *getLabelBeforeInsn(const MachineInstr *MI);

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -166,10 +166,6 @@ const char CFGuardName[] = "Control Flow Guard";
 const char CFGuardDescription[] = "Control Flow Guard";
 const char CodeViewLineTablesGroupName[] = "linetables";
 const char CodeViewLineTablesGroupDescription[] = "CodeView Line Tables";
-const char PPTimerName[] = "emit";
-const char PPTimerDescription[] = "Pseudo Probe Emission";
-const char PPGroupName[] = "pseudo probe";
-const char PPGroupDescription[] = "Pseudo Probe Emission";
 
 STATISTIC(EmittedInsts, "Number of machine instrs printed");
 
@@ -555,27 +551,24 @@ bool AsmPrinter::doInitialization(Module &M) {
   if (MAI->doesSupportDebugInformation()) {
     bool EmitCodeView = M.getCodeViewFlag();
     if (EmitCodeView && TM.getTargetTriple().isOSWindows()) {
-      Handlers.emplace_back(std::make_unique<CodeViewDebug>(this),
-                            DbgTimerName, DbgTimerDescription,
-                            CodeViewLineTablesGroupName,
-                            CodeViewLineTablesGroupDescription);
+      DebugHandlers.emplace_back(std::make_unique<CodeViewDebug>(this),
+                                 DbgTimerName, DbgTimerDescription,
+                                 CodeViewLineTablesGroupName,
+                                 CodeViewLineTablesGroupDescription);
     }
     if (!EmitCodeView || M.getDwarfVersion()) {
       assert(MMI && "MMI could not be nullptr here!");
       if (MMI->hasDebugInfo()) {
         DD = new DwarfDebug(this);
-        Handlers.emplace_back(std::unique_ptr<DwarfDebug>(DD), DbgTimerName,
-                              DbgTimerDescription, DWARFGroupName,
-                              DWARFGroupDescription);
+        DebugHandlers.emplace_back(std::unique_ptr<DwarfDebug>(DD),
+                                   DbgTimerName, DbgTimerDescription,
+                                   DWARFGroupName, DWARFGroupDescription);
       }
     }
   }
 
-  if (M.getNamedMetadata(PseudoProbeDescMetadataName)) {
-    PP = new PseudoProbeHandler(this);
-    Handlers.emplace_back(std::unique_ptr<PseudoProbeHandler>(PP), PPTimerName,
-                          PPTimerDescription, PPGroupName, PPGroupDescription);
-  }
+  if (M.getNamedMetadata(PseudoProbeDescMetadataName))
+    PP = std::make_unique<PseudoProbeHandler>(this);
 
   switch (MAI->getExceptionHandlingType()) {
   case ExceptionHandling::None:
@@ -642,7 +635,12 @@ bool AsmPrinter::doInitialization(Module &M) {
                           CFGuardDescription, DWARFGroupName,
                           DWARFGroupDescription);
 
-  for (const HandlerInfo &HI : Handlers) {
+  for (const auto &HI : DebugHandlers) {
+    NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                       HI.TimerGroupDescription, TimePassesIsEnabled);
+    HI.Handler->beginModule(&M);
+  }
+  for (const auto &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->beginModule(&M);
@@ -793,10 +791,9 @@ void AsmPrinter::emitGlobalVariable(const GlobalVariable *GV) {
   // sections and expected to be contiguous (e.g. ObjC metadata).
   const Align Alignment = getGVAlignment(GV, DL);
 
-  for (const HandlerInfo &HI : Handlers) {
-    NamedRegionTimer T(HI.TimerName, HI.TimerDescription,
-                       HI.TimerGroupName, HI.TimerGroupDescription,
-                       TimePassesIsEnabled);
+  for (auto &HI : DebugHandlers) {
+    NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                       HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->setSymbolSize(GVSym, Size);
   }
 
@@ -1069,12 +1066,18 @@ void AsmPrinter::emitFunctionHeader() {
   }
 
   // Emit pre-function debug and/or EH information.
-  for (const HandlerInfo &HI : Handlers) {
+  for (const auto &HI : DebugHandlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->beginFunction(MF);
+    HI.Handler->beginBasicBlockSection(MF->front());
   }
-  for (const HandlerInfo &HI : Handlers) {
+  for (const auto &HI : Handlers) {
+    NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                       HI.TimerGroupDescription, TimePassesIsEnabled);
+    HI.Handler->beginFunction(MF);
+  }
+  for (const auto &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->beginBasicBlockSection(MF->front());
@@ -1773,7 +1776,7 @@ void AsmPrinter::emitFunctionBody() {
       if (MDNode *MD = MI.getPCSections())
         emitPCSectionsLabel(*MF, *MD);
 
-      for (const HandlerInfo &HI : Handlers) {
+      for (const auto &HI : DebugHandlers) {
         NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                            HI.TimerGroupDescription, TimePassesIsEnabled);
         HI.Handler->beginInstruction(&MI);
@@ -1871,7 +1874,7 @@ void AsmPrinter::emitFunctionBody() {
       if (MCSymbol *S = MI.getPostInstrSymbol())
         OutStreamer->emitLabel(S);
 
-      for (const HandlerInfo &HI : Handlers) {
+      for (const auto &HI : DebugHandlers) {
         NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                            HI.TimerGroupDescription, TimePassesIsEnabled);
         HI.Handler->endInstruction();
@@ -2006,13 +2009,18 @@ void AsmPrinter::emitFunctionBody() {
   // Call endBasicBlockSection on the last block now, if it wasn't already
   // called.
   if (!MF->back().isEndSection()) {
-    for (const HandlerInfo &HI : Handlers) {
+    for (const auto &HI : DebugHandlers) {
+      NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                         HI.TimerGroupDescription, TimePassesIsEnabled);
+      HI.Handler->endBasicBlockSection(MF->back());
+    }
+    for (const auto &HI : Handlers) {
       NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                          HI.TimerGroupDescription, TimePassesIsEnabled);
       HI.Handler->endBasicBlockSection(MF->back());
     }
   }
-  for (const HandlerInfo &HI : Handlers) {
+  for (const auto &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->markFunctionEnd();
@@ -2025,7 +2033,12 @@ void AsmPrinter::emitFunctionBody() {
   emitJumpTableInfo();
 
   // Emit post-function debug and/or EH information.
-  for (const HandlerInfo &HI : Handlers) {
+  for (const auto &HI : DebugHandlers) {
+    NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                       HI.TimerGroupDescription, TimePassesIsEnabled);
+    HI.Handler->endFunction(MF);
+  }
+  for (const auto &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->endFunction(MF);
@@ -2466,7 +2479,12 @@ bool AsmPrinter::doFinalization(Module &M) {
     emitGlobalIFunc(M, IFunc);
 
   // Finalize debug and EH information.
-  for (const HandlerInfo &HI : Handlers) {
+  for (const auto &HI : DebugHandlers) {
+    NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                       HI.TimerGroupDescription, TimePassesIsEnabled);
+    HI.Handler->endModule();
+  }
+  for (const auto &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->endModule();
@@ -2476,6 +2494,8 @@ bool AsmPrinter::doFinalization(Module &M) {
   // keeping all the user-added handlers alive until the AsmPrinter is
   // destroyed.
   Handlers.erase(Handlers.begin() + NumUserHandlers, Handlers.end());
+  DebugHandlers.erase(DebugHandlers.begin() + NumUserDebugHandlers,
+                      DebugHandlers.end());
   DD = nullptr;
 
   // If the target wants to know about weak references, print them all.
@@ -3990,7 +4010,7 @@ static void emitBasicBlockLoopComments(const MachineBasicBlock &MBB,
 void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
   // End the previous funclet and start a new one.
   if (MBB.isEHFuncletEntry()) {
-    for (const HandlerInfo &HI : Handlers) {
+    for (const auto &HI : Handlers) {
       HI.Handler->endFunclet();
       HI.Handler->beginFunclet(MBB);
     }
@@ -4062,17 +4082,23 @@ void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
   // With BB sections, each basic block must handle CFI information on its own
   // if it begins a section (Entry block call is handled separately, next to
   // beginFunction).
-  if (MBB.isBeginSection() && !MBB.isEntryBlock())
-    for (const HandlerInfo &HI : Handlers)
+  if (MBB.isBeginSection() && !MBB.isEntryBlock()) {
+    for (const auto &HI : DebugHandlers)
+      HI.Handler->beginBasicBlockSection(MBB);
+    for (const auto &HI : Handlers)
       HI.Handler->beginBasicBlockSection(MBB);
+  }
 }
 
 void AsmPrinter::emitBasicBlockEnd(const MachineBasicBlock &MBB) {
   // Check if CFI information needs to be updated for this MBB with basic block
   // sections.
-  if (MBB.isEndSection())
-    for (const HandlerInfo &HI : Handlers)
+  if (MBB.isEndSection()) {
+    for (const auto &HI : DebugHandlers)
+      HI.Handler->endBasicBlockSection(MBB);
+    for (const auto &HI : Handlers)
       HI.Handler->endBasicBlockSection(MBB);
+  }
 }
 
 void AsmPrinter::emitVisibility(MCSymbol *Sym, unsigned Visibility,

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h

@@ -517,8 +517,6 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
 
   void beginModule(Module *M) override;
 
-  void setSymbolSize(const MCSymbol *, uint64_t) override {}
-
   /// Emit the COFF section that holds the line table information.
   void endModule() override;
 

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

@@ -100,6 +100,8 @@ DbgVariableLocation::extractFromMachineInstruction(
 
 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
 
+DebugHandlerBase::~DebugHandlerBase() = default;
+
 void DebugHandlerBase::beginModule(Module *M) {
   if (M->debug_compile_units().empty())
     Asm = nullptr;

llvm/lib/CodeGen/AsmPrinter/EHStreamer.h

@@ -150,11 +150,6 @@ class LLVM_LIBRARY_VISIBILITY EHStreamer : public AsmPrinterHandler {
   EHStreamer(AsmPrinter *A);
   ~EHStreamer() override;
 
-  // Unused.
-  void setSymbolSize(const MCSymbol *Sym, uint64_t Size) override {}
-  void beginInstruction(const MachineInstr *MI) override {}
-  void endInstruction() override {}
-
   /// Return `true' if this is a call to a function marked `nounwind'. Return
   /// `false' otherwise.
   static bool callToNoUnwindFunction(const MachineInstr *MI);

llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.cpp

@@ -20,8 +20,6 @@
 
 using namespace llvm;
 
-PseudoProbeHandler::~PseudoProbeHandler() = default;
-
 void PseudoProbeHandler::emitPseudoProbe(uint64_t Guid, uint64_t Index,
                                          uint64_t Type, uint64_t Attr,
                                          const DILocation *DebugLoc) {