Add a pass to collect dropped var stats for MIR.

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

Author: rastogishubham

llvm/include/llvm/CodeGen/DroppedVariableStats.h

@@ -7,7 +7,7 @@
 ///===---------------------------------------------------------------------===//
 /// \file
 /// Dropped Variable Statistics for Debug Information. Reports any number
-/// of #dbg_value that get dropped due to an optimization pass.
+/// of #dbg_values or DBG_VALUEs that get dropped due to an optimization pass.
 ///
 ///===---------------------------------------------------------------------===//
 
@@ -160,6 +160,40 @@ class DroppedVariableStatsIR : public DroppedVariableStats {
   }
 };
 
+/// 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:
+  /// 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,
+                                                 std::string FuncOrModName);
+};
+
 } // 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/DroppedVariableStats.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/Pass.h"
 
@@ -67,6 +68,7 @@ class MachineFunctionPass : public FunctionPass {
   MachineFunctionProperties RequiredProperties;
   MachineFunctionProperties SetProperties;
   MachineFunctionProperties ClearedProperties;
+  DroppedVariableStatsMIR DroppedVarStatsMF;
 
   /// createPrinterPass - Get a machine function printer pass.
   Pass *createPrinterPass(raw_ostream &O,

llvm/lib/CodeGen/DroppedVariableStats.cpp

@@ -7,7 +7,7 @@
 ///===---------------------------------------------------------------------===//
 /// \file
 /// Dropped Variable Statistics for Debug Information. Reports any number
-/// of #dbg_value that get dropped due to an optimization pass.
+/// of #dbg_values or DBG_VALUEs that get dropped due to an optimization pass.
 ///
 ///===---------------------------------------------------------------------===//
 
@@ -147,4 +147,76 @@ void DroppedVariableStatsIR::registerCallbacks(
       });
   PIC.registerAfterPassInvalidatedCallback(
       [this](StringRef P, const PreservedAnalyses &PA) { return cleanup(); });
+}
+
+void DroppedVariableStatsMIR::runOnMachineFunction(const MachineFunction *MF,
+                                                   bool Before) {
+  auto &DebugVariables = DebugVariablesStack.back()[&MF->getFunction()];
+  auto &VarIDSet = (Before ? DebugVariables.DebugVariablesBefore
+                           : DebugVariables.DebugVariablesAfter);
+  auto &InlinedAtsMap = InlinedAts.back();
+  auto FuncName = MF->getName();
+  if (Before)
+    InlinedAtsMap.try_emplace(FuncName, DenseMap<VarID, DILocation *>());
+  VarIDSet = DenseSet<VarID>();
+  for (const auto &MBB : *MF) {
+    for (const auto &MI : MBB) {
+      if (MI.isDebugValueLike()) {
+        auto *DbgVar = MI.getDebugVariable();
+        if (!DbgVar)
+          continue;
+        auto DbgLoc = MI.getDebugLoc();
+        VarID Key{DbgVar->getScope(), DbgLoc->getInlinedAtScope(), DbgVar};
+        VarIDSet.insert(Key);
+        if (Before)
+          InlinedAtsMap[FuncName].try_emplace(Key, DbgLoc.getInlinedAt());
+      }
+    }
+  }
+}
+
+void DroppedVariableStatsMIR::calculateDroppedVarStatsOnMachineFunction(
+    const MachineFunction *MF, StringRef PassID, std::string FuncOrModName) {
+  unsigned DroppedCount = 0;
+  StringRef FuncName = MF->getName();
+  DebugVariables &DbgVariables = DebugVariablesStack.back()[&MF->getFunction()];
+  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;
+    const DIScope *DbgValScope = std::get<0>(Var);
+    for (const auto &MBB : *MF) {
+      for (const auto &MI : MBB) {
+        auto *DbgLoc = MI.getDebugLoc().get();
+        if (!DbgLoc)
+          continue;
+
+        auto *Scope = DbgLoc->getScope();
+        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++;
+            break;
+          }
+        }
+      }
+    }
+    removeVarFromAllSets(Var, &MF->getFunction());
+  }
+  if (DroppedCount > 0) {
+    llvm::outs() << "MachineFunction" << ", " << PassID << ", " << DroppedCount
+                 << ", " << FuncOrModName << "\n";
+    PassDroppedVariables = true;
+  } else
+    PassDroppedVariables = false;
 }

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/MIR/CMakeLists.txt

@@ -16,6 +16,7 @@ set(LLVM_LINK_COMPONENTS
 add_llvm_unittest(MIRTests
   MachineMetadata.cpp
   MachineStableHashTest.cpp
+  DroppedVariableStatsMIRTest.cpp
   )
 
 target_link_libraries(MIRTests PRIVATE LLVMTestingSupport)