[IR] De-virtualize ~Value to save a vptr

Summary:
Implements PR889

Removing the virtual table pointer from Value saves 1% of RSS when doing
LTO of llc on Linux. The impact on time was positive, but too noisy to
conclusively say that performance improved. Here is a link to the
spreadsheet with the original data:

https://docs.google.com/spreadsheets/d/1F4FHir0qYnV0MEp2sYYp_BuvnJgWlWPhWOwZ6LbW7W4/edit?usp=sharing

This change makes it invalid to directly delete a Value, User, or
Instruction pointer. Instead, such code can be rewritten to a null check
and a call Value::deleteValue(). Value objects tend to have their
lifetimes managed through iplist, so for the most part, this isn't a big
deal.  However, there are some places where LLVM deletes values, and
those places had to be migrated to deleteValue.  I have also created
llvm::unique_value, which has a custom deleter, so it can be used in
place of std::unique_ptr<Value>.

I had to add the "DerivedUser" Deleter escape hatch for MemorySSA, which
derives from User outside of lib/IR. Code in IR cannot include MemorySSA
headers or call the MemoryAccess object destructors without introducing
a circular dependency, so we need some level of indirection.
Unfortunately, no class derived from User may have any virtual methods,
because adding a virtual method would break User::getHungOffOperands(),
which assumes that it can find the use list immediately prior to the
User object. I've added a static_assert to the appropriate OperandTraits
templates to help people avoid this trap.

Reviewers: chandlerc, mehdi_amini, pete, dberlin, george.burgess.iv

Reviewed By: chandlerc

Subscribers: krytarowski, eraman, george.burgess.iv, mzolotukhin, Prazek, nlewycky, hans, inglorion, pcc, tejohnson, dberlin, llvm-commits

Differential Revision: https://reviews.llvm.org/D31261

llvm-svn: 303362

9 files changed, 10 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index c04646eed49..0490d93f645 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -2057,7 +2057,7 @@ bool GVN::performScalarPRE(Instruction *CurInst) {
     if (!performScalarPREInsertion(PREInstr, PREPred, ValNo)) {
       // If we failed insertion, make sure we remove the instruction.
       DEBUG(verifyRemoved(PREInstr));
-      delete PREInstr;
+      PREInstr->deleteValue();
       return false;
     }
   }
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 54ab80e448f..ada22ae38eb 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1906,7 +1906,7 @@ bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred(
             {BB->getModule()->getDataLayout(), TLI, nullptr, nullptr, New})) {
       ValueMapping[&*BI] = IV;
       if (!New->mayHaveSideEffects()) {
-        delete New;
+        New->deleteValue();
         New = nullptr;
       }
     } else {
diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 2ba9265566a..7312d97f8ef 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -347,7 +347,7 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
       // in the map.
       ValueMap[Inst] = V;
       if (!C->mayHaveSideEffects()) {
-        delete C;
+        C->deleteValue();
         C = nullptr;
       }
     } else {
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 53320bff088..a20890b2260 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -1582,7 +1582,7 @@ Value *ReassociatePass::OptimizeAdd(Instruction *I,
     }
 
     // No need for extra uses anymore.
-    delete DummyInst;
+    DummyInst->deleteValue();
 
     unsigned NumAddedValues = NewMulOps.size();
     Value *V = EmitAddTreeOfValues(I, NewMulOps);
diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index ed7df091b55..24bd0a2b7bd 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -2443,7 +2443,7 @@ private:
                         "insert");
       LI.replaceAllUsesWith(V);
       Placeholder->replaceAllUsesWith(&LI);
-      delete Placeholder;
+      Placeholder->deleteValue();
     } else {
       LI.replaceAllUsesWith(V);
     }
diff --git a/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
index 2be3f5c533b..8b8d6590aa6 100644
--- a/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
@@ -693,7 +693,7 @@ bool StraightLineStrengthReduce::runOnFunction(Function &F) {
       UnlinkedInst->setOperand(I, nullptr);
       RecursivelyDeleteTriviallyDeadInstructions(Op);
     }
-    delete UnlinkedInst;
+    UnlinkedInst->deleteValue();
   }
   bool Ret = !UnlinkedInstructions.empty();
   UnlinkedInstructions.clear();
diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 4aa26fd14fe..bf2ab7c55be 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -317,7 +317,7 @@ void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
 
         if (!NewInst->mayHaveSideEffects()) {
           VMap[&*II] = V;
-          delete NewInst;
+          NewInst->deleteValue();
           continue;
         }
       }
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index b44bc74d655..5a04cac0653 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2235,7 +2235,7 @@ static bool FoldCondBranchOnPHI(BranchInst *BI, const DataLayout &DL,
         if (!BBI->use_empty())
           TranslateMap[&*BBI] = V;
         if (!N->mayHaveSideEffects()) {
-          delete N; // Instruction folded away, don't need actual inst
+          N->deleteValue(); // Instruction folded away, don't need actual inst
           N = nullptr;
         }
       } else {
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 64013d6d687..e6f78e6b94a 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -578,12 +578,12 @@ private:
   void eraseInstruction(Instruction *I) {
     I->removeFromParent();
     I->dropAllReferences();
-    DeletedInstructions.push_back(std::unique_ptr<Instruction>(I));
+    DeletedInstructions.emplace_back(I);
   }
 
   /// Temporary store for deleted instructions. Instructions will be deleted
   /// eventually when the BoUpSLP is destructed.
-  SmallVector<std::unique_ptr<Instruction>, 8> DeletedInstructions;
+  SmallVector<unique_value, 8> DeletedInstructions;
 
   /// A list of values that need to extracted out of the tree.
   /// This list holds pairs of (Internal Scalar : External User). External User