Add a pass to collect dropped var stats for MIR (#120780)

This patch uses the DroppedVariableStats class to add dropped variable
statistics for MIR passes.

Reland 1c082c9cd12efaa67a32c5da89a328c458ed51c5

llvm/include/llvm/CodeGen/DroppedVariableStatsMIR.h

@@ -0,0 +1,70 @@
+///===- DroppedVariableStatsMIR.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_VALUEs that get dropped due to an optimization pass.
+///
+///===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_DROPPEDVARIABLESTATSMIR_H
+#define LLVM_CODEGEN_DROPPEDVARIABLESTATSMIR_H
+
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/Passes/DroppedVariableStats.h"
+
+namespace llvm {
+
+/// A class to collect and print dropped debug information due to MIR
+/// optimization passes. After every MIR pass is run, it will print how many
+/// #DBG_VALUEs were dropped due to that pass.
+class DroppedVariableStatsMIR : public DroppedVariableStats {
+public:
+  DroppedVariableStatsMIR() : llvm::DroppedVariableStats(false) {}
+
+  void runBeforePass(StringRef PassID, MachineFunction *MF) {
+    if (PassID == "Debug Variable Analysis")
+      return;
+    setup();
+    return runOnMachineFunction(MF, true);
+  }
+
+  void runAfterPass(StringRef PassID, MachineFunction *MF) {
+    if (PassID == "Debug Variable Analysis")
+      return;
+    runOnMachineFunction(MF, false);
+    calculateDroppedVarStatsOnMachineFunction(MF, PassID, MF->getName().str());
+    cleanup();
+  }
+
+private:
+  const MachineFunction *MFunc;
+  /// Populate DebugVariablesBefore, DebugVariablesAfter, InlinedAts before or
+  /// after a pass has run to facilitate dropped variable calculation for an
+  /// llvm::MachineFunction.
+  void runOnMachineFunction(const MachineFunction *MF, bool Before);
+  /// Iterate over all Instructions in a MachineFunction and report any dropped
+  /// debug information.
+  void calculateDroppedVarStatsOnMachineFunction(const MachineFunction *MF,
+                                                 StringRef PassID,
+                                                 StringRef FuncOrModName);
+  /// Override base class method to run on an llvm::MachineFunction
+  /// 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;
+};
+
+} // namespace llvm
+
+#endif

llvm/include/llvm/CodeGen/MachineFunctionPass.h

@@ -18,6 +18,7 @@
 #ifndef LLVM_CODEGEN_MACHINEFUNCTIONPASS_H
 #define LLVM_CODEGEN_MACHINEFUNCTIONPASS_H
 
+#include "llvm/CodeGen/DroppedVariableStatsMIR.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/Pass.h"
 
@@ -67,6 +68,7 @@ private:
   MachineFunctionProperties RequiredProperties;
   MachineFunctionProperties SetProperties;
   MachineFunctionProperties ClearedProperties;
+  DroppedVariableStatsMIR DroppedVarStatsMF;
 
   /// createPrinterPass - Get a machine function printer pass.
   Pass *createPrinterPass(raw_ostream &O,

llvm/lib/CodeGen/CMakeLists.txt

@@ -50,6 +50,7 @@ add_llvm_component_library(LLVMCodeGen
   DeadMachineInstructionElim.cpp
   DetectDeadLanes.cpp
   DFAPacketizer.cpp
+  DroppedVariableStatsMIR.cpp
   DwarfEHPrepare.cpp
   EarlyIfConversion.cpp
   EdgeBundles.cpp

llvm/lib/CodeGen/DroppedVariableStatsMIR.cpp

@@ -0,0 +1,77 @@
+///===- DroppedVariableStatsMIR.cpp ---------------------------------------===//
+///
+/// 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_VALUEs that get dropped due to an optimization pass.
+///
+///===---------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/DroppedVariableStatsMIR.h"
+
+using namespace llvm;
+
+void DroppedVariableStatsMIR::runOnMachineFunction(const MachineFunction *MF,
+                                                   bool Before) {
+  auto &DebugVariables = DebugVariablesStack.back()[&MF->getFunction()];
+  auto FuncName = MF->getName();
+  MFunc = MF;
+  run(DebugVariables, FuncName, Before);
+}
+
+void DroppedVariableStatsMIR::calculateDroppedVarStatsOnMachineFunction(
+    const MachineFunction *MF, StringRef PassID, StringRef FuncOrModName) {
+  MFunc = MF;
+  StringRef FuncName = MF->getName();
+  const Function *Func = &MF->getFunction();
+  DebugVariables &DbgVariables = DebugVariablesStack.back()[Func];
+  calculateDroppedStatsAndPrint(DbgVariables, FuncName, PassID, FuncOrModName,
+                                "MachineFunction", Func);
+}
+
+void DroppedVariableStatsMIR::visitEveryInstruction(
+    unsigned &DroppedCount, DenseMap<VarID, DILocation *> &InlinedAtsMap,
+    VarID Var) {
+  unsigned PrevDroppedCount = DroppedCount;
+  const DIScope *DbgValScope = std::get<0>(Var);
+  for (const auto &MBB : *MFunc) {
+    for (const auto &MI : MBB) {
+      if (!MI.isDebugInstr()) {
+        auto *DbgLoc = MI.getDebugLoc().get();
+        if (!DbgLoc)
+          continue;
+
+        auto *Scope = DbgLoc->getScope();
+        if (updateDroppedCount(DbgLoc, Scope, DbgValScope, InlinedAtsMap, Var,
+                               DroppedCount))
+          break;
+      }
+    }
+    if (PrevDroppedCount != DroppedCount) {
+      PrevDroppedCount = DroppedCount;
+      break;
+    }
+  }
+}
+
+void DroppedVariableStatsMIR::visitEveryDebugRecord(
+    DenseSet<VarID> &VarIDSet,
+    DenseMap<StringRef, DenseMap<VarID, DILocation *>> &InlinedAtsMap,
+    StringRef FuncName, bool Before) {
+  for (const auto &MBB : *MFunc) {
+    for (const auto &MI : MBB) {
+      if (MI.isDebugValueLike()) {
+        auto *DbgVar = MI.getDebugVariable();
+        if (!DbgVar)
+          continue;
+        auto DbgLoc = MI.getDebugLoc();
+        populateVarIDSetAndInlinedMap(DbgVar, DbgLoc, VarIDSet, InlinedAtsMap,
+                                      FuncName, Before);
+      }
+    }
+  }
+}

llvm/lib/CodeGen/MachineFunctionPass.cpp

@@ -32,6 +32,11 @@
 using namespace llvm;
 using namespace ore;
 
+static cl::opt<bool> DroppedVarStatsMIR(
+    "dropped-variable-stats-mir", cl::Hidden,
+    cl::desc("Dump dropped debug variables stats for MIR passes"),
+    cl::init(false));
+
 Pass *MachineFunctionPass::createPrinterPass(raw_ostream &O,
                                              const std::string &Banner) const {
   return createMachineFunctionPrinterPass(O, Banner);
@@ -91,7 +96,15 @@ bool MachineFunctionPass::runOnFunction(Function &F) {
 
   MFProps.reset(ClearedProperties);
 
-  bool RV = runOnMachineFunction(MF);
+  bool RV;
+  if (DroppedVarStatsMIR) {
+    auto PassName = getPassName();
+    DroppedVarStatsMF.runBeforePass(PassName, &MF);
+    RV = runOnMachineFunction(MF);
+    DroppedVarStatsMF.runAfterPass(PassName, &MF);
+  } else {
+    RV = runOnMachineFunction(MF);
+  }
 
   if (ShouldEmitSizeRemarks) {
     // We wanted size remarks. Check if there was a change to the number of

llvm/unittests/CodeGen/CMakeLists.txt

@@ -27,6 +27,7 @@ add_llvm_unittest(CodeGenTests
   CCStateTest.cpp
   DIEHashTest.cpp
   DIETest.cpp
+  DroppedVariableStatsMIRTest.cpp
   DwarfStringPoolEntryRefTest.cpp
   InstrRefLDVTest.cpp
   LowLevelTypeTest.cpp