[NFC] Move DroppedVariableStats to its own file (llvm#120711)

Move DroppedVariableStats code to its own file and change the class to
have an extensible design so that we can use it to add dropped
statistics to MIR passes and the instruction selector.

Also moved class DroppedVariableStatsIR to its own file.

Reland 2de7881

(cherry picked from commit 5717a99)

(cherry picked from commit 0b5b09b)

Author: rastogishubham

llvm/include/llvm/Passes/DroppedVariableStats.h

@@ -0,0 +1,225 @@
+///===- DroppedVariableStats.h - Opt Diagnostics -*- C++ -*----------------===//
+///
+/// Part of the LLVM Project, under the Apache License v2.0 with LLVM
+/// Exceptions. See https://llvm.org/LICENSE.txt for license information.
+/// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+///
+///===---------------------------------------------------------------------===//
+/// \file
+/// Dropped Variable Statistics for Debug Information. Reports any number
+/// of #dbg_value that get dropped due to an optimization pass.
+///
+///===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_DROPPEDVARIABLESTATS_H
+#define LLVM_CODEGEN_DROPPEDVARIABLESTATS_H
+
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/PassInstrumentation.h"
+
+namespace llvm {
+
+/// A unique key that represents a debug variable.
+/// First const DIScope *: Represents the scope of the debug variable.
+/// Second const DIScope *: Represents the InlinedAt scope of the debug
+/// variable. const DILocalVariable *: It is a pointer to the debug variable
+/// itself.
+using VarID =
+    std::tuple<const DIScope *, const DIScope *, const DILocalVariable *>;
+
+/// A base class to collect and print dropped debug information variable
+/// statistics.
+class DroppedVariableStats {
+public:
+  DroppedVariableStats(bool DroppedVarStatsEnabled)
+      : DroppedVariableStatsEnabled(DroppedVarStatsEnabled) {
+    if (DroppedVarStatsEnabled)
+      llvm::outs()
+          << "Pass Level, Pass Name, Num of Dropped Variables, Func or "
+             "Module Name\n";
+  };
+
+  virtual ~DroppedVariableStats() {}
+
+  // We intend this to be unique per-compilation, thus no copies.
+  DroppedVariableStats(const DroppedVariableStats &) = delete;
+  void operator=(const DroppedVariableStats &) = delete;
+
+  bool getPassDroppedVariables() { return PassDroppedVariables; }
+
+protected:
+  void setup() {
+    DebugVariablesStack.push_back(
+        {DenseMap<const Function *, DebugVariables>()});
+    InlinedAts.push_back(
+        {DenseMap<StringRef, DenseMap<VarID, DILocation *>>()});
+  }
+
+  void cleanup() {
+    assert(!DebugVariablesStack.empty() &&
+           "DebugVariablesStack shouldn't be empty!");
+    assert(!InlinedAts.empty() && "InlinedAts shouldn't be empty!");
+    DebugVariablesStack.pop_back();
+    InlinedAts.pop_back();
+  }
+
+  bool DroppedVariableStatsEnabled = false;
+  struct DebugVariables {
+    /// DenseSet of VarIDs before an optimization pass has run.
+    DenseSet<VarID> DebugVariablesBefore;
+    /// DenseSet of VarIDs after an optimization pass has run.
+    DenseSet<VarID> DebugVariablesAfter;
+  };
+
+protected:
+  /// A stack of a DenseMap, that maps DebugVariables for every pass to an
+  /// llvm::Function. A stack is used because an optimization pass can call
+  /// other passes.
+  SmallVector<DenseMap<const Function *, DebugVariables>> DebugVariablesStack;
+
+  /// A DenseSet tracking whether a scope was visited before.
+  DenseSet<const DIScope *> VisitedScope;
+  /// A stack of DenseMaps, which map the name of an llvm::Function to a
+  /// DenseMap of VarIDs and their inlinedAt locations before an optimization
+  /// pass has run.
+  SmallVector<DenseMap<StringRef, DenseMap<VarID, DILocation *>>> InlinedAts;
+  /// Calculate the number of dropped variables in an llvm::Function or
+  /// llvm::MachineFunction and print the relevant information to stdout.
+  void calculateDroppedStatsAndPrint(DebugVariables &DbgVariables,
+                                     StringRef FuncName, StringRef PassID,
+                                     StringRef FuncOrModName,
+                                     StringRef PassLevel,
+                                     const Function *Func) {
+    unsigned DroppedCount = 0;
+    DenseSet<VarID> &DebugVariablesBeforeSet =
+        DbgVariables.DebugVariablesBefore;
+    DenseSet<VarID> &DebugVariablesAfterSet = DbgVariables.DebugVariablesAfter;
+    DenseMap<VarID, DILocation *> &InlinedAtsMap = InlinedAts.back()[FuncName];
+    // Find an Instruction that shares the same scope as the dropped #dbg_value
+    // or has a scope that is the child of the scope of the #dbg_value, and has
+    // an inlinedAt equal to the inlinedAt of the #dbg_value or it's inlinedAt
+    // chain contains the inlinedAt of the #dbg_value, if such an Instruction is
+    // found, debug information is dropped.
+    for (VarID Var : DebugVariablesBeforeSet) {
+      if (DebugVariablesAfterSet.contains(Var))
+        continue;
+      visitEveryInstruction(DroppedCount, InlinedAtsMap, Var);
+      removeVarFromAllSets(Var, Func);
+    }
+    if (DroppedCount > 0) {
+      llvm::outs() << PassLevel << ", " << PassID << ", " << DroppedCount
+                   << ", " << FuncOrModName << "\n";
+      PassDroppedVariables = true;
+    } else
+      PassDroppedVariables = false;
+  }
+
+  /// Check if a \p Var has been dropped or is a false positive. Also update the
+  /// \p DroppedCount if a debug variable is dropped.
+  bool updateDroppedCount(DILocation *DbgLoc, const DIScope *Scope,
+                          const DIScope *DbgValScope,
+                          DenseMap<VarID, DILocation *> &InlinedAtsMap,
+                          VarID Var, unsigned &DroppedCount) {
+    // If the Scope is a child of, or equal to the DbgValScope and is inlined at
+    // the Var's InlinedAt location, return true to signify that the Var has
+    // been dropped.
+    if (isScopeChildOfOrEqualTo(Scope, DbgValScope))
+      if (isInlinedAtChildOfOrEqualTo(DbgLoc->getInlinedAt(),
+                                      InlinedAtsMap[Var])) {
+        // Found another instruction in the variable's scope, so there exists a
+        // break point at which the variable could be observed. Count it as
+        // dropped.
+        DroppedCount++;
+        return true;
+      }
+    return false;
+  }
+  /// Run code to populate relevant data structures over an llvm::Function or
+  /// llvm::MachineFunction.
+  void run(DebugVariables &DbgVariables, StringRef FuncName, bool Before) {
+    auto &VarIDSet = (Before ? DbgVariables.DebugVariablesBefore
+                             : DbgVariables.DebugVariablesAfter);
+    auto &InlinedAtsMap = InlinedAts.back();
+    if (Before)
+      InlinedAtsMap.try_emplace(FuncName, DenseMap<VarID, DILocation *>());
+    VarIDSet = DenseSet<VarID>();
+    visitEveryDebugRecord(VarIDSet, InlinedAtsMap, FuncName, Before);
+  }
+  /// Populate the VarIDSet and InlinedAtMap with the relevant information
+  /// needed for before and after pass analysis to determine dropped variable
+  /// status.
+  void populateVarIDSetAndInlinedMap(
+      const DILocalVariable *DbgVar, DebugLoc DbgLoc, DenseSet<VarID> &VarIDSet,
+      DenseMap<StringRef, DenseMap<VarID, DILocation *>> &InlinedAtsMap,
+      StringRef FuncName, bool Before) {
+    VarID Key{DbgVar->getScope(), DbgLoc->getInlinedAtScope(), DbgVar};
+    VarIDSet.insert(Key);
+    if (Before)
+      InlinedAtsMap[FuncName].try_emplace(Key, DbgLoc.getInlinedAt());
+  }
+  /// Visit every llvm::Instruction or llvm::MachineInstruction and check if the
+  /// debug variable denoted by its ID \p Var may have been dropped by an
+  /// optimization pass.
+  virtual void
+  visitEveryInstruction(unsigned &DroppedCount,
+                        DenseMap<VarID, DILocation *> &InlinedAtsMap,
+                        VarID Var) = 0;
+  /// Visit every debug record in an llvm::Function or llvm::MachineFunction
+  /// and call populateVarIDSetAndInlinedMap on it.
+  virtual void visitEveryDebugRecord(
+      DenseSet<VarID> &VarIDSet,
+      DenseMap<StringRef, DenseMap<VarID, DILocation *>> &InlinedAtsMap,
+      StringRef FuncName, bool Before) = 0;
+
+private:
+  /// Remove a dropped debug variable's VarID from all Sets in the
+  /// DroppedVariablesBefore stack.
+  void removeVarFromAllSets(VarID Var, const Function *F) {
+    // Do not remove Var from the last element, it will be popped from the
+    // stack.
+    for (auto &DebugVariablesMap : llvm::drop_end(DebugVariablesStack))
+      DebugVariablesMap[F].DebugVariablesBefore.erase(Var);
+  }
+  /// Return true if \p Scope is the same as \p DbgValScope or a child scope of
+  /// \p DbgValScope, return false otherwise.
+  bool isScopeChildOfOrEqualTo(const DIScope *Scope,
+                               const DIScope *DbgValScope) {
+    while (Scope != nullptr) {
+      if (VisitedScope.find(Scope) == VisitedScope.end()) {
+        VisitedScope.insert(Scope);
+        if (Scope == DbgValScope) {
+          VisitedScope.clear();
+          return true;
+        }
+        Scope = Scope->getScope();
+      } else {
+        VisitedScope.clear();
+        return false;
+      }
+    }
+    return false;
+  }
+  /// Return true if \p InlinedAt is the same as \p DbgValInlinedAt or part of
+  /// the InlinedAt chain, return false otherwise.
+  bool isInlinedAtChildOfOrEqualTo(const DILocation *InlinedAt,
+                                   const DILocation *DbgValInlinedAt) {
+    if (DbgValInlinedAt == InlinedAt)
+      return true;
+    if (!DbgValInlinedAt)
+      return false;
+    auto *IA = InlinedAt;
+    while (IA) {
+      if (IA == DbgValInlinedAt)
+        return true;
+      IA = IA->getInlinedAt();
+    }
+    return false;
+  }
+  bool PassDroppedVariables = false;
+};
+
+} // namespace llvm
+
+#endif

llvm/include/llvm/Passes/DroppedVariableStatsIR.h

@@ -0,0 +1,101 @@
+///===- DroppedVariableStatsIR.h - Opt Diagnostics -*- C++ -*--------------===//
+///
+/// Part of the LLVM Project, under the Apache License v2.0 with LLVM
+/// Exceptions. See https://llvm.org/LICENSE.txt for license information.
+/// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+///
+///===---------------------------------------------------------------------===//
+/// \file
+/// Dropped Variable Statistics for Debug Information. Reports any number
+/// of #dbg_value that get dropped due to an optimization pass.
+///
+///===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_DROPPEDVARIABLESTATSIR_H
+#define LLVM_CODEGEN_DROPPEDVARIABLESTATSIR_H
+
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Passes/DroppedVariableStats.h"
+
+namespace llvm {
+
+/// A class to collect and print dropped debug information due to LLVM IR
+/// optimization passes. After every LLVM IR pass is run, it will print how many
+/// #dbg_values were dropped due to that pass.
+class DroppedVariableStatsIR : public DroppedVariableStats {
+public:
+  DroppedVariableStatsIR(bool DroppedVarStatsEnabled)
+      : llvm::DroppedVariableStats(DroppedVarStatsEnabled) {}
+
+  void runBeforePass(Any IR) {
+    setup();
+    if (const auto *M = unwrapIR<Module>(IR))
+      return this->runOnModule(M, true);
+    if (const auto *F = unwrapIR<Function>(IR))
+      return this->runOnFunction(F, true);
+  }
+
+  void runAfterPass(StringRef P, Any IR) {
+    if (const auto *M = unwrapIR<Module>(IR))
+      runAfterPassModule(P, M);
+    else if (const auto *F = unwrapIR<Function>(IR))
+      runAfterPassFunction(P, F);
+    cleanup();
+  }
+
+  void registerCallbacks(PassInstrumentationCallbacks &PIC);
+
+private:
+  const Function *Func;
+
+  void runAfterPassFunction(StringRef PassID, const Function *F) {
+    runOnFunction(F, false);
+    calculateDroppedVarStatsOnFunction(F, PassID, F->getName().str(),
+                                       "Function");
+  }
+
+  void runAfterPassModule(StringRef PassID, const Module *M) {
+    runOnModule(M, false);
+    calculateDroppedVarStatsOnModule(M, PassID, M->getName().str(), "Module");
+  }
+  /// Populate DebugVariablesBefore, DebugVariablesAfter, InlinedAts before or
+  /// after a pass has run to facilitate dropped variable calculation for an
+  /// llvm::Function.
+  void runOnFunction(const Function *F, bool Before);
+  /// Iterate over all Instructions in a Function and report any dropped debug
+  /// information.
+  void calculateDroppedVarStatsOnFunction(const Function *F, StringRef PassID,
+                                          StringRef FuncOrModName,
+                                          StringRef PassLevel);
+  /// Populate DebugVariablesBefore, DebugVariablesAfter, InlinedAts before or
+  /// after a pass has run to facilitate dropped variable calculation for an
+  /// llvm::Module. Calls runOnFunction on every Function in the Module.
+  void runOnModule(const Module *M, bool Before);
+  /// Iterate over all Functions in a Module and report any dropped debug
+  /// information. Will call calculateDroppedVarStatsOnFunction on every
+  /// Function.
+  void calculateDroppedVarStatsOnModule(const Module *M, StringRef PassID,
+                                        StringRef FuncOrModName,
+                                        StringRef PassLevel);
+  /// Override base class method to run on an llvm::Function specifically.
+  virtual void
+  visitEveryInstruction(unsigned &DroppedCount,
+                        DenseMap<VarID, DILocation *> &InlinedAtsMap,
+                        VarID Var) override;
+
+  /// Override base class method to run on #dbg_values specifically.
+  virtual void visitEveryDebugRecord(
+      DenseSet<VarID> &VarIDSet,
+      DenseMap<StringRef, DenseMap<VarID, DILocation *>> &InlinedAtsMap,
+      StringRef FuncName, bool Before) override;
+
+  template <typename IRUnitT> static const IRUnitT *unwrapIR(Any IR) {
+    const IRUnitT **IRPtr = llvm::any_cast<const IRUnitT *>(&IR);
+    return IRPtr ? *IRPtr : nullptr;
+  }
+};
+
+} // namespace llvm
+
+#endif