[IPT] Drop cache less eagerly in GVN and LoopSafetyInfo

Current strategy of dropping `InstructionPrecedenceTracking` cache is to
invalidate the entire basic block whenever we change its contents. In fact,
`InstructionPrecedenceTracking` has 2 internal strictures: `OrderedInstructions`
that is needed to be invalidated whenever the contents changes, and the map
with first special instructions in block. This second map does not need an
update if we add/remove a non-special instuction because it cannot
affect the contents of this map.

This patch changes API of `InstructionPrecedenceTracking` so that it now
accounts for reasons under which we invalidate blocks. This should lead
to much less recalculations of the map and should save us some compile time
because in practice we don't typically add/remove special instructions.

Differential Revision: https://reviews.llvm.org/D54462
Reviewed By: efriedma

llvm-svn: 350694

Author: Max Kazantsev

llvm/include/llvm/Analysis/InstructionPrecedenceTracking.h

@@ -75,8 +75,14 @@ class InstructionPrecedenceTracking {
   virtual ~InstructionPrecedenceTracking() = default;
 
 public:
-  /// Clears cached information about this particular block.
-  void invalidateBlock(const BasicBlock *BB);
+  /// Notifies this tracking that we are going to insert a new instruction \p
+  /// Inst to the basic block \p BB. It makes all necessary updates to internal
+  /// caches to keep them consistent.
+  void insertInstructionTo(const Instruction *Inst, const BasicBlock *BB);
+
+  /// Notifies this tracking that we are going to remove the instruction \p Inst
+  /// It makes all necessary updates to internal caches to keep them consistent.
+  void removeInstruction(const Instruction *Inst);
 
   /// Invalidates all information from this tracking.
   void clear();

llvm/include/llvm/Analysis/MustExecute.h

@@ -151,9 +151,9 @@ class ICFLoopSafetyInfo: public LoopSafetyInfo {
       const;
 
   /// Inform the safety info that we are planning to insert a new instruction
-  /// into the basic block \p BB. It will make all cache updates to keep it
-  /// correct after this insertion.
-  void insertInstructionTo(const BasicBlock *BB);
+  /// \p Inst into the basic block \p BB. It will make all cache updates to keep
+  /// it correct after this insertion.
+  void insertInstructionTo(const Instruction *Inst, const BasicBlock *BB);
 
   /// Inform safety info that we are planning to remove the instruction \p Inst
   /// from its block. It will make all cache updates to keep it correct after

llvm/lib/Analysis/InstructionPrecedenceTracking.cpp

@@ -99,9 +99,17 @@ void InstructionPrecedenceTracking::validateAll() const {
 }
 #endif
 
-void InstructionPrecedenceTracking::invalidateBlock(const BasicBlock *BB) {
+void InstructionPrecedenceTracking::insertInstructionTo(const Instruction *Inst,
+                                                        const BasicBlock *BB) {
+  if (isSpecialInstruction(Inst))
+    FirstSpecialInsts.erase(BB);
   OI.invalidateBlock(BB);
-  FirstSpecialInsts.erase(BB);
+}
+
+void InstructionPrecedenceTracking::removeInstruction(const Instruction *Inst) {
+  if (isSpecialInstruction(Inst))
+    FirstSpecialInsts.erase(Inst->getParent());
+  OI.invalidateBlock(Inst->getParent());
 }
 
 void InstructionPrecedenceTracking::clear() {

llvm/lib/Analysis/MustExecute.cpp

@@ -83,16 +83,15 @@ void ICFLoopSafetyInfo::computeLoopSafetyInfo(const Loop *CurLoop) {
   computeBlockColors(CurLoop);
 }
 
-void ICFLoopSafetyInfo::insertInstructionTo(const BasicBlock *BB) {
-  ICF.invalidateBlock(BB);
-  MW.invalidateBlock(BB);
+void ICFLoopSafetyInfo::insertInstructionTo(const Instruction *Inst,
+                                            const BasicBlock *BB) {
+  ICF.insertInstructionTo(Inst, BB);
+  MW.insertInstructionTo(Inst, BB);
 }
 
 void ICFLoopSafetyInfo::removeInstruction(const Instruction *Inst) {
-  // TODO: So far we just conservatively drop cache, but maybe we can not do it
-  // when Inst is not an ICF instruction. Follow-up on that.
-  ICF.invalidateBlock(Inst->getParent());
-  MW.invalidateBlock(Inst->getParent());
+  ICF.removeInstruction(Inst);
+  MW.removeInstruction(Inst);
 }
 
 void LoopSafetyInfo::computeBlockColors(const Loop *CurLoop) {

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -2079,10 +2079,9 @@ bool GVN::processBlock(BasicBlock *BB) {
       salvageDebugInfo(*I);
       if (MD) MD->removeInstruction(I);
       LLVM_DEBUG(verifyRemoved(I));
+      ICF->removeInstruction(I);
       I->eraseFromParent();
     }
-
-    ICF->invalidateBlock(BB);
     InstrsToErase.clear();
 
     if (AtStart)
@@ -2301,7 +2300,7 @@ bool GVN::performScalarPRE(Instruction *CurInst) {
   LLVM_DEBUG(verifyRemoved(CurInst));
   // FIXME: Intended to be markInstructionForDeletion(CurInst), but it causes
   // some assertion failures.
-  ICF->invalidateBlock(CurrentBlock);
+  ICF->removeInstruction(CurInst);
   CurInst->eraseFromParent();
   ++NumGVNInstr;
 

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -742,13 +742,13 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
         auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0);
         auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor);
         ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags());
-        SafetyInfo->insertInstructionTo(I.getParent());
+        SafetyInfo->insertInstructionTo(ReciprocalDivisor, I.getParent());
         ReciprocalDivisor->insertBefore(&I);
 
         auto Product =
             BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor);
         Product->setFastMathFlags(I.getFastMathFlags());
-        SafetyInfo->insertInstructionTo(I.getParent());
+        SafetyInfo->insertInstructionTo(Product, I.getParent());
         Product->insertAfter(&I);
         I.replaceAllUsesWith(Product);
         eraseInstruction(I, *SafetyInfo, CurAST);
@@ -1189,7 +1189,7 @@ static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
 static void moveInstructionBefore(Instruction &I, Instruction &Dest,
                                   ICFLoopSafetyInfo &SafetyInfo) {
   SafetyInfo.removeInstruction(&I);
-  SafetyInfo.insertInstructionTo(Dest.getParent());
+  SafetyInfo.insertInstructionTo(&I, Dest.getParent());
   I.moveBefore(&Dest);
 }