[ADCE] Refactoring for new functionality (NFC)

[david2050]

Summary

This is another refactoring to break up the one function into three logical components functions.
Another non-functional change before we start added in features.

[nadav]

lib/Transforms/Scalar/ADCE.cpp

51

Please use doxygen style comments (three slashes) and a period at the end of the sentence. Please do the same for the other comments above.

Also, please name the parameter. If the name does not give a good indication of what the parameter is you can use '\p' to describe the parameter.,

68

Doxygen, period, just like above.

76

Typo here. 'gig'

[david2050]

Doxygen style comments with periods. Fix spelling of Aggressive

[mehdi_amini]

lib/Transforms/Scalar/ADCE.cpp

51

Also, just a nit, I'm used to to read Return true for... instead of True for.

[majnemer]

lib/Transforms/Scalar/ADCE.cpp

90

Would it make sense to use !isInstructionTriviallyDead here instead?

91–93

Perhaps the logic for profile instrumentation can be sunk into isInstructionTriviallyDead?

[david2050]

Save David's suggestions. Add parameter name

[david2050]

lib/Transforms/Scalar/ADCE.cpp

91–93

I tried to reply via email but it got lost in space. I prefer to not make this change until I get the my changes landed just for stability of baseline. But I will get to to it before we are done.

[majnemer]

LGTM

lib/Transforms/Scalar/ADCE.cpp

91–93

Sure, sounds reasonable to me.

lib/Transforms/Scalar/ADCE.cpp

class AgggressiveDeadCodeElimination {
   Function &F;
   // Instructions known to be live
   SmallPtrSet<Instruction *, 32> Alive;
   // Instructions known to be live where we need to mark
   // reaching definitions as live
   SmallVector<Instruction *, 128> Worklist;
   // Debug info scopes around a live instruction
   SmallPtrSet<const Metadata *, 32> AliveScopes;
-  
+  void initialize();
+  // True for operations which are always treated as live
+  bool isAlwaysLive(Instruction &);
+  // True for instrumentation instructions for value profiling
+  bool isInstrumentsConstant(Instruction &I);
+  
+
+  // Propagate liveness to reaching definitions
+  void markLiveInstructions();
+  // Mark an instruction as live
+  void markLive(Instruction &I);
+  
   void collectLiveScopes(const DILocalScope &LS);
   void collectLiveScopes(const DILocation &DL);
-  bool isInstrumentsConstant(Instruction &I);
+  
+
+  // Remove instructions not marked live, return if any any instruction
+  // was removed
+  bool removeDeadInstructions();
+
 public:
   AgggressiveDeadCodeElimination(Function &F) : F(F) {}
-  bool aggressiveDCE();
+  bool performDeadCodeElimination();
 };
 }
 
-void AgggressiveDeadCodeElimination::collectLiveScopes(
-    const DILocalScope &LS) {
-  if (!AliveScopes.insert(&LS).second)
-    return;
-
-  if (isa<DISubprogram>(LS))
-    return;
-
-  // Tail-recurse through the scope chain.
-  collectLiveScopes(cast<DILocalScope>(*LS.getScope()));
+bool AgggressiveDeadCodeElimination::performDeadCodeElimination() {
+  initialize();
+  markLiveInstructions();
+  return removeDeadInstructions();
 }
 
-void AgggressiveDeadCodeElimination::collectLiveScopes(const DILocation &DL) {
-  // Even though DILocations are not scopes, shove them into AliveScopes so we
-  // don't revisit them.
-  if (!AliveScopes.insert(&DL).second)
-    return;
-
-  // Collect live scopes from the scope chain.
-  collectLiveScopes(*DL.getScope());
+void AgggressiveDeadCodeElimination::initialize() {
+  // Collect the set of "root" instructions that are known live.
+  for (Instruction &I : instructions(F))
+    if (isAlwaysLive(I))
+      markLive(I);
+}
 
-  // Tail-recurse through the inlined-at chain.
-  if (const DILocation *IA = DL.getInlinedAt())
-    collectLiveScopes(*IA);
+bool AgggressiveDeadCodeElimination::isAlwaysLive(Instruction &I) {
+  if (isa<TerminatorInst>(I) || I.isEHPad() || I.mayHaveSideEffects()) {
+    // Skip any value profile instrumentation calls if they are
+    // instrumenting constants.
+    if (!isInstrumentsConstant(I))
+      return true;
+  }
+  return false;
 }
 
 // Check if this instruction is a runtime call for value profiling and
 // if it's instrumenting a constant.
 bool AgggressiveDeadCodeElimination::isInstrumentsConstant(Instruction &I) {
   if (CallInst *CI = dyn_cast<CallInst>(&I))
     if (Function *Callee = CI->getCalledFunction())
       if (Callee->getName().equals(getInstrProfValueProfFuncName()))
         if (isa<Constant>(CI->getArgOperand(0)))
           return true;
   return false;
 }
 
-bool AgggressiveDeadCodeElimination::aggressiveDCE() {
-
-  // Collect the set of "root" instructions that are known live.
-  for (Instruction &I : instructions(F)) {
-    if (isa<TerminatorInst>(I) || I.isEHPad() || I.mayHaveSideEffects()) {
-      // Skip any value profile instrumentation calls if they are
-      // instrumenting constants.
-      if (isInstrumentsConstant(I))
-        continue;
-      Alive.insert(&I);
-      Worklist.push_back(&I);
-    }
-  }
+void AgggressiveDeadCodeElimination::markLiveInstructions() {
 
   // Propagate liveness backwards to operands.  Keep track of live debug info
   // scopes.
   while (!Worklist.empty()) {
     Instruction *Curr = Worklist.pop_back_val();
 
     // Collect the live debug info scopes attached to this instruction.
     if (const DILocation *DL = Curr->getDebugLoc())
       collectLiveScopes(*DL);
 
     for (Use &OI : Curr->operands()) {
       if (Instruction *Inst = dyn_cast<Instruction>(OI))
-        if (Alive.insert(Inst).second)
-          Worklist.push_back(Inst);
-    }
-  }
+        markLive(*Inst);
+    }
 
+void AgggressiveDeadCodeElimination::collectLiveScopes(const DILocalScope &LS) {
+  if (!AliveScopes.insert(&LS).second)
+    return;
+  
+  if (isa<DISubprogram>(LS))
+    return;
+  
+  // Tail-recurse through the scope chain.
+  collectLiveScopes(cast<DILocalScope>(*LS.getScope()));
+}
+
+void AgggressiveDeadCodeElimination::collectLiveScopes(const DILocation &DL) {
+  // Even though DILocations are not scopes, shove them into AliveScopes so we
+  // don't revisit them.
+  if (!AliveScopes.insert(&DL).second)
+    return;
+  
+  // Collect live scopes from the scope chain.
+  collectLiveScopes(*DL.getScope());
+  
+  // Tail-recurse through the inlined-at chain.
+  if (const DILocation *IA = DL.getInlinedAt())
+    collectLiveScopes(*IA);
+}
+
+void AgggressiveDeadCodeElimination::markLive(Instruction &I) {
+  if (!Alive.insert(&I).second)
+    return;
+  Worklist.push_back(&I);
+}
+
+bool AgggressiveDeadCodeElimination::removeDeadInstructions() {
+
   // The inverse of the live set is the dead set.  These are those instructions
   // which have no side effects and do not influence the control flow or return
   // value of the function, and may therefore be deleted safely.
   // NOTE: We reuse the Worklist vector here for memory efficiency.
   for (Instruction &I : instructions(F)) {
     // Check if the instruction is alive.
     if (Alive.count(&I))
       continue;
for (Instruction *&I : Worklist) {
     ++NumRemoved;
     I->eraseFromParent();
   }
 
   return !Worklist.empty();
 }
 
 PreservedAnalyses ADCEPass::run(Function &F, FunctionAnalysisManager &) {
-  if (!AgggressiveDeadCodeElimination(F).aggressiveDCE())
+  if (!AgggressiveDeadCodeElimination(F).performDeadCodeElimination())
     return PreservedAnalyses::all();
 
   // FIXME: This should also 'preserve the CFG'.
   auto PA = PreservedAnalyses();
   PA.preserve<GlobalsAA>();
   return PA;
 }
 
 namespace {
 struct ADCELegacyPass : public FunctionPass {
   static char ID; // Pass identification, replacement for typeid
   ADCELegacyPass() : FunctionPass(ID) {
     initializeADCELegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
-    return AgggressiveDeadCodeElimination(F).aggressiveDCE();
+    return AgggressiveDeadCodeElimination(F).performDeadCodeElimination();
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     AU.addPreserved<GlobalsAAWrapperPass>();
   }
 };
 }
 
 char ADCELegacyPass::ID = 0;
 INITIALIZE_PASS(ADCELegacyPass, "adce", "Aggressive Dead Code Elimination",
                 false, false)
 
 FunctionPass *llvm::createAggressiveDCEPass() { return new ADCELegacyPass(); }