[IPSCCP] Move the IPSCCP run function under the IPO directory.

[labrinea]

Summary

The LLVMipo library no longer depends on the Scalar component. The shared functions between IPSCCP and SCCP have been moved under Utils, in the SCCPSolver.

This is preliminary work for D126455, in order to break cyclic dependecy of LLVM libraries.

[labrinea]

llvm/lib/Transforms/Scalar/SCCP.cpp

61–64

Some of these were used in IPSCCP, but it seems wrong to me. Now that I've separated SCCP from IPSCCP, I've duplicated any shared statistics.

[labrinea]

Rebase

[labrinea]

The previous commit regressed some buildbots:

undefined reference to `llvm::createBitTrackingDCEPass()'
undefined reference to `llvm::createAlignmentFromAssumptionsPass()'
undefined reference to `llvm::createLoopUnrollPass(int, bool, bool, int, int, int, int, int, int)'
undefined reference to `llvm::createLICMPass(unsigned int, unsigned int, bool)'
undefined reference to `llvm::createWarnMissedTransformationsPass()'
undefined reference to `llvm::createAlignmentFromAssumptionsPass()'
undefined reference to `llvm::createCallSiteSplittingPass()'
undefined reference to `llvm::createCFGSimplificationPass(llvm::SimplifyCFGOptions, std::function<bool (llvm::Function const&)>)'
undefined reference to `llvm::createFloat2IntPass()'
undefined reference to `llvm::createLowerConstantIntrinsicsPass()'
undefined reference to `llvm::createLoopRotatePass(int, bool)'
undefined reference to `llvm::createLoopDistributePass()'
undefined reference to `llvm::createLoopSinkPass()'
undefined reference to `llvm::createInstSimplifyLegacyPass()'
undefined reference to `llvm::createDivRemPairsPass()'
undefined reference to `llvm::createCFGSimplificationPass(llvm::SimplifyCFGOptions, std::function<bool (llvm::Function const&)>)'
undefined reference to `llvm::SetLicmMssaOptCap'
undefined reference to `llvm::SetLicmMssaNoAccForPromotionCap'
undefined reference to `llvm::ForgetSCEVInLoopUnroll'

This is fixed by reintroducing one of the two occurences of 'Scalar' under the LINK_COMPONENTS.

[thakis]

llvm/lib/Transforms/IPO/CMakeLists.txt

68–69

Since this is now still here, doesn't this render "The LLVMipo library no longer depends on the Scalar component." incorrect?

[labrinea]

llvm/lib/Transforms/IPO/CMakeLists.txt

68–69

Right. The commit message is outdated. What this patch achieves is that D126455 no longer needs to add Scalar->IPO dependency which would create a cycle.

llvm/include/llvm/Transforms/Scalar/SCCP.h

 struct AnalysisResultsForFn;
 
 /// This pass performs function-level constant propagation and merging.
 class SCCPPass : public PassInfoMixin<SCCPPass> {
 public:
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 };
 
-bool runIPSCCP(Module &M, const DataLayout &DL,
-               std::function<const TargetLibraryInfo &(Function &)> GetTLI,
-               function_ref<AnalysisResultsForFn(Function &)> getAnalysis);
-
 bool runFunctionSpecialization(
     Module &M, const DataLayout &DL,
     std::function<TargetLibraryInfo &(Function &)> GetTLI,
     std::function<TargetTransformInfo &(Function &)> GetTTI,
     std::function<AssumptionCache &(Function &)> GetAC,
     function_ref<AnalysisResultsForFn(Function &)> GetAnalysis);
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_SCALAR_SCCP_H

llvm/include/llvm/Transforms/Utils/SCCPSolver.h

 // This file implements Sparse Conditional Constant Propagation (SCCP) utility.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_TRANSFORMS_UTILS_SCCPSOLVER_H
 #define LLVM_TRANSFORMS_UTILS_SCCPSOLVER_H
 
 #include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/DomTreeUpdater.h"
 #include "llvm/Transforms/Utils/PredicateInfo.h"
 #include <vector>
 
 namespace llvm {
 class Argument;
 class BasicBlock;
 class CallInst;
public:
   /// this method to erase a function from the module (e.g., if it has been
   /// completely specialized and is no longer needed).
   void markFunctionUnreachable(Function *F);
 
   void visit(Instruction *I);
   void visitCall(CallInst &I);
 };
 
+//===----------------------------------------------------------------------===//
+//
+/// Helper functions used by the SCCP and IPSCCP passes.
+//
+bool isConstant(const ValueLatticeElement &LV);
+
+bool isOverdefined(const ValueLatticeElement &LV);
+
+bool simplifyInstsInBlock(SCCPSolver &Solver, BasicBlock &BB,
+                          SmallPtrSetImpl<Value *> &InsertedValues,
+                          Statistic &InstRemovedStat,
+                          Statistic &InstReplacedStat);
+
+bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V);
+
+bool removeNonFeasibleEdges(const llvm::SCCPSolver &Solver, BasicBlock *BB,
+                            DomTreeUpdater &DTU,
+                            BasicBlock *&NewUnreachableBB);
 } // namespace llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_SCCPSOLVER_H

llvm/lib/Transforms/IPO/CMakeLists.txt

add_llvm_component_library(LLVMipo
   BitReader
   BitWriter
   Core
   FrontendOpenMP
   InstCombine
   IRReader
   Linker
   Object
   ProfileData
-  Scalar
   Support
   TransformUtils
   Vectorize
   Instrumentation
-  Scalar
   )

llvm/lib/Transforms/IPO/FunctionSpecialization.cpp

 
 using FuncList = SmallVectorImpl<Function *>;
 using CallArgBinding = std::pair<CallBase *, Constant *>;
 using CallSpecBinding = std::pair<CallBase *, SpecializationInfo>;
 // We are using MapVector because it guarantees deterministic iteration
 // order across executions.
 using SpecializationMap = SmallMapVector<CallBase *, SpecializationInfo, 8>;
 
-// Helper to check if \p LV is either a constant or a constant
-// range with a single element. This should cover exactly the same cases as the
-// old ValueLatticeElement::isConstant() and is intended to be used in the
-// transition to ValueLatticeElement.
-static bool isConstant(const ValueLatticeElement &LV) {
-  return LV.isConstant() ||
-         (LV.isConstantRange() && LV.getConstantRange().isSingleElement());
-}
-
-// Helper to check if \p LV is either overdefined or a constant int.
-static bool isOverdefined(const ValueLatticeElement &LV) {
-  return !LV.isUnknownOrUndef() && !isConstant(LV);
-}
-
 static Constant *getPromotableAlloca(AllocaInst *Alloca, CallInst *Call) {
   Value *StoreValue = nullptr;
   for (auto *User : Alloca->users()) {
     // We can't use llvm::isAllocaPromotable() as that would fail because of
     // the usage in the CallInst, which is what we check here.
     if (User == Call)
       continue;
     if (auto *Bitcast = dyn_cast<BitCastInst>(User)) {

llvm/lib/Transforms/IPO/SCCP.cpp

 //===-- SCCP.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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements Interprocedural Sparse Conditional Constant Propagation.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/IPO/SCCP.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/PostDominators.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueLattice.h"
+#include "llvm/Analysis/ValueLatticeUtils.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Support/ModRef.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/Scalar/SCCP.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/SCCPSolver.h"
 
 using namespace llvm;
 
+#define DEBUG_TYPE "sccp"
+
+STATISTIC(NumInstRemoved, "Number of instructions removed");
+STATISTIC(NumArgsElimed ,"Number of arguments constant propagated");
+STATISTIC(NumGlobalConst, "Number of globals found to be constant");
+STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
+STATISTIC(NumInstReplaced,
+          "Number of instructions replaced with (simpler) instruction");
+
+static void findReturnsToZap(Function &F,
+                             SmallVector<ReturnInst *, 8> &ReturnsToZap,
+                             SCCPSolver &Solver) {
+  // We can only do this if we know that nothing else can call the function.
+  if (!Solver.isArgumentTrackedFunction(&F))
+    return;
+
+  if (Solver.mustPreserveReturn(&F)) {
+    LLVM_DEBUG(
+        dbgs()
+        << "Can't zap returns of the function : " << F.getName()
+        << " due to present musttail or \"clang.arc.attachedcall\" call of "
+           "it\n");
+    return;
+  }
+
+  assert(
+      all_of(F.users(),
+             [&Solver](User *U) {
+               if (isa<Instruction>(U) &&
+                   !Solver.isBlockExecutable(cast<Instruction>(U)->getParent()))
+                 return true;
+               // Non-callsite uses are not impacted by zapping. Also, constant
+               // uses (like blockaddresses) could stuck around, without being
+               // used in the underlying IR, meaning we do not have lattice
+               // values for them.
+               if (!isa<CallBase>(U))
+                 return true;
+               if (U->getType()->isStructTy()) {
+                 return all_of(Solver.getStructLatticeValueFor(U),
+                               [](const ValueLatticeElement &LV) {
+                                 return !isOverdefined(LV);
+                               });
+               }
+               return !isOverdefined(Solver.getLatticeValueFor(U));
+             }) &&
+      "We can only zap functions where all live users have a concrete value");
+
+  for (BasicBlock &BB : F) {
+    if (CallInst *CI = BB.getTerminatingMustTailCall()) {
+      LLVM_DEBUG(dbgs() << "Can't zap return of the block due to present "
+                        << "musttail call : " << *CI << "\n");
+      (void)CI;
+      return;
+    }
+
+    if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator()))
+      if (!isa<UndefValue>(RI->getOperand(0)))
+        ReturnsToZap.push_back(RI);
+  }
+}
+
+static bool runIPSCCP(
+    Module &M, const DataLayout &DL,
+    std::function<const TargetLibraryInfo &(Function &)> GetTLI,
+    function_ref<AnalysisResultsForFn(Function &)> getAnalysis) {
+  SCCPSolver Solver(DL, GetTLI, M.getContext());
+
+  // Loop over all functions, marking arguments to those with their addresses
+  // taken or that are external as overdefined.
+  for (Function &F : M) {
+    if (F.isDeclaration())
+      continue;
+
+    Solver.addAnalysis(F, getAnalysis(F));
+
+    // Determine if we can track the function's return values. If so, add the
+    // function to the solver's set of return-tracked functions.
+    if (canTrackReturnsInterprocedurally(&F))
+      Solver.addTrackedFunction(&F);
+
+    // Determine if we can track the function's arguments. If so, add the
+    // function to the solver's set of argument-tracked functions.
+    if (canTrackArgumentsInterprocedurally(&F)) {
+      Solver.addArgumentTrackedFunction(&F);
+      continue;
+    }
+
+    // Assume the function is called.
+    Solver.markBlockExecutable(&F.front());
+
+    // Assume nothing about the incoming arguments.
+    for (Argument &AI : F.args())
+      Solver.markOverdefined(&AI);
+  }
+
+  // Determine if we can track any of the module's global variables. If so, add
+  // the global variables we can track to the solver's set of tracked global
+  // variables.
+  for (GlobalVariable &G : M.globals()) {
+    G.removeDeadConstantUsers();
+    if (canTrackGlobalVariableInterprocedurally(&G))
+      Solver.trackValueOfGlobalVariable(&G);
+  }
+
+  // Solve for constants.
+  bool ResolvedUndefs = true;
+  Solver.solve();
+  while (ResolvedUndefs) {
+    LLVM_DEBUG(dbgs() << "RESOLVING UNDEFS\n");
+    ResolvedUndefs = false;
+    for (Function &F : M) {
+      if (Solver.resolvedUndefsIn(F))
+        ResolvedUndefs = true;
+    }
+    if (ResolvedUndefs)
+      Solver.solve();
+  }
+
+  bool MadeChanges = false;
+
+  // Iterate over all of the instructions in the module, replacing them with
+  // constants if we have found them to be of constant values.
+
+  for (Function &F : M) {
+    if (F.isDeclaration())
+      continue;
+
+    SmallVector<BasicBlock *, 512> BlocksToErase;
+
+    if (Solver.isBlockExecutable(&F.front())) {
+      bool ReplacedPointerArg = false;
+      for (Argument &Arg : F.args()) {
+        if (!Arg.use_empty() && tryToReplaceWithConstant(Solver, &Arg)) {
+          ReplacedPointerArg |= Arg.getType()->isPointerTy();
+          ++NumArgsElimed;
+        }
+      }
+
+      // If we replaced an argument, we may now also access a global (currently
+      // classified as "other" memory). Update memory attribute to reflect this.
+      if (ReplacedPointerArg) {
+        auto UpdateAttrs = [&](AttributeList AL) {
+          MemoryEffects ME = AL.getMemoryEffects();
+          if (ME == MemoryEffects::unknown())
+            return AL;
+
+          ME |= MemoryEffects(MemoryEffects::Other,
+                              ME.getModRef(MemoryEffects::ArgMem));
+          return AL.addFnAttribute(
+              F.getContext(),
+              Attribute::getWithMemoryEffects(F.getContext(), ME));
+        };
+
+        F.setAttributes(UpdateAttrs(F.getAttributes()));
+        for (User *U : F.users()) {
+          auto *CB = dyn_cast<CallBase>(U);
+          if (!CB || CB->getCalledFunction() != &F)
+            continue;
+
+          CB->setAttributes(UpdateAttrs(CB->getAttributes()));
+        }
+      }
+      MadeChanges |= ReplacedPointerArg;
+    }
+
+    SmallPtrSet<Value *, 32> InsertedValues;
+    for (BasicBlock &BB : F) {
+      if (!Solver.isBlockExecutable(&BB)) {
+        LLVM_DEBUG(dbgs() << "  BasicBlock Dead:" << BB);
+        ++NumDeadBlocks;
+
+        MadeChanges = true;
+
+        if (&BB != &F.front())
+          BlocksToErase.push_back(&BB);
+        continue;
+      }
+
+      MadeChanges |= simplifyInstsInBlock(Solver, BB, InsertedValues,
+                                          NumInstRemoved, NumInstReplaced);
+    }
+
+    DomTreeUpdater DTU = Solver.getDTU(F);
+    // Change dead blocks to unreachable. We do it after replacing constants
+    // in all executable blocks, because changeToUnreachable may remove PHI
+    // nodes in executable blocks we found values for. The function's entry
+    // block is not part of BlocksToErase, so we have to handle it separately.
+    for (BasicBlock *BB : BlocksToErase) {
+      NumInstRemoved += changeToUnreachable(BB->getFirstNonPHI(),
+                                            /*PreserveLCSSA=*/false, &DTU);
+    }
+    if (!Solver.isBlockExecutable(&F.front()))
+      NumInstRemoved += changeToUnreachable(F.front().getFirstNonPHI(),
+                                            /*PreserveLCSSA=*/false, &DTU);
+
+    BasicBlock *NewUnreachableBB = nullptr;
+    for (BasicBlock &BB : F)
+      MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU, NewUnreachableBB);
+
+    for (BasicBlock *DeadBB : BlocksToErase)
+      if (!DeadBB->hasAddressTaken())
+        DTU.deleteBB(DeadBB);
+
+    for (BasicBlock &BB : F) {
+      for (Instruction &Inst : llvm::make_early_inc_range(BB)) {
+        if (Solver.getPredicateInfoFor(&Inst)) {
+          if (auto *II = dyn_cast<IntrinsicInst>(&Inst)) {
+            if (II->getIntrinsicID() == Intrinsic::ssa_copy) {
+              Value *Op = II->getOperand(0);
+              Inst.replaceAllUsesWith(Op);
+              Inst.eraseFromParent();
+            }
+          }
+        }
+      }
+    }
+  }
+
+  // If we inferred constant or undef return values for a function, we replaced
+  // all call uses with the inferred value.  This means we don't need to bother
+  // actually returning anything from the function.  Replace all return
+  // instructions with return undef.
+  //
+  // Do this in two stages: first identify the functions we should process, then
+  // actually zap their returns.  This is important because we can only do this
+  // if the address of the function isn't taken.  In cases where a return is the
+  // last use of a function, the order of processing functions would affect
+  // whether other functions are optimizable.
+  SmallVector<ReturnInst*, 8> ReturnsToZap;
+
+  for (const auto &I : Solver.getTrackedRetVals()) {
+    Function *F = I.first;
+    const ValueLatticeElement &ReturnValue = I.second;
+
+    // If there is a known constant range for the return value, add !range
+    // metadata to the function's call sites.
+    if (ReturnValue.isConstantRange() &&
+        !ReturnValue.getConstantRange().isSingleElement()) {
+      // Do not add range metadata if the return value may include undef.
+      if (ReturnValue.isConstantRangeIncludingUndef())
+        continue;
+
+      auto &CR = ReturnValue.getConstantRange();
+      for (User *User : F->users()) {
+        auto *CB = dyn_cast<CallBase>(User);
+        if (!CB || CB->getCalledFunction() != F)
+          continue;
+
+        // Limit to cases where the return value is guaranteed to be neither
+        // poison nor undef. Poison will be outside any range and currently
+        // values outside of the specified range cause immediate undefined
+        // behavior.
+        if (!isGuaranteedNotToBeUndefOrPoison(CB, nullptr, CB))
+          continue;
+
+        // Do not touch existing metadata for now.
+        // TODO: We should be able to take the intersection of the existing
+        // metadata and the inferred range.
+        if (CB->getMetadata(LLVMContext::MD_range))
+          continue;
+
+        LLVMContext &Context = CB->getParent()->getContext();
+        Metadata *RangeMD[] = {
+            ConstantAsMetadata::get(ConstantInt::get(Context, CR.getLower())),
+            ConstantAsMetadata::get(ConstantInt::get(Context, CR.getUpper()))};
+        CB->setMetadata(LLVMContext::MD_range, MDNode::get(Context, RangeMD));
+      }
+      continue;
+    }
+    if (F->getReturnType()->isVoidTy())
+      continue;
+    if (isConstant(ReturnValue) || ReturnValue.isUnknownOrUndef())
+      findReturnsToZap(*F, ReturnsToZap, Solver);
+  }
+
+  for (auto *F : Solver.getMRVFunctionsTracked()) {
+    assert(F->getReturnType()->isStructTy() &&
+           "The return type should be a struct");
+    StructType *STy = cast<StructType>(F->getReturnType());
+    if (Solver.isStructLatticeConstant(F, STy))
+      findReturnsToZap(*F, ReturnsToZap, Solver);
+  }
+
+  // Zap all returns which we've identified as zap to change.
+  SmallSetVector<Function *, 8> FuncZappedReturn;
+  for (ReturnInst *RI : ReturnsToZap) {
+    Function *F = RI->getParent()->getParent();
+    RI->setOperand(0, UndefValue::get(F->getReturnType()));
+    // Record all functions that are zapped.
+    FuncZappedReturn.insert(F);
+  }
+
+  // Remove the returned attribute for zapped functions and the
+  // corresponding call sites.
+  for (Function *F : FuncZappedReturn) {
+    for (Argument &A : F->args())
+      F->removeParamAttr(A.getArgNo(), Attribute::Returned);
+    for (Use &U : F->uses()) {
+      // Skip over blockaddr users.
+      if (isa<BlockAddress>(U.getUser()))
+        continue;
+      CallBase *CB = cast<CallBase>(U.getUser());
+      for (Use &Arg : CB->args())
+        CB->removeParamAttr(CB->getArgOperandNo(&Arg), Attribute::Returned);
+    }
+  }
+
+  // If we inferred constant or undef values for globals variables, we can
+  // delete the global and any stores that remain to it.
+  for (const auto &I : make_early_inc_range(Solver.getTrackedGlobals())) {
+    GlobalVariable *GV = I.first;
+    if (isOverdefined(I.second))
+      continue;
+    LLVM_DEBUG(dbgs() << "Found that GV '" << GV->getName()
+                      << "' is constant!\n");
+    while (!GV->use_empty()) {
+      StoreInst *SI = cast<StoreInst>(GV->user_back());
+      SI->eraseFromParent();
+      MadeChanges = true;
+    }
+    M.getGlobalList().erase(GV);
+    ++NumGlobalConst;
+  }
+
+  return MadeChanges;
+}
+
 PreservedAnalyses IPSCCPPass::run(Module &M, ModuleAnalysisManager &AM) {
   const DataLayout &DL = M.getDataLayout();
   auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
   auto GetTLI = [&FAM](Function &F) -> const TargetLibraryInfo & {
     return FAM.getResult<TargetLibraryAnalysis>(F);
   };
   auto getAnalysis = [&FAM](Function &F) -> AnalysisResultsForFn {
     DominatorTree &DT = FAM.getResult<DominatorTreeAnalysis>(F);

llvm/lib/Transforms/Scalar/SCCP.cpp

 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/DomTreeUpdater.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
-#include "llvm/Analysis/ValueLattice.h"
-#include "llvm/Analysis/ValueLatticeUtils.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
-#include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
-#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/User.h"
 #include "llvm/IR/Value.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/SCCPSolver.h"
 #include <cassert>
 #include <utility>
 #include <vector>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "sccp"
 
 STATISTIC(NumInstRemoved, "Number of instructions removed");
 STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
 STATISTIC(NumInstReplaced,
           "Number of instructions replaced with (simpler) instruction");
 
-STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
-STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
-STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
-STATISTIC(
-    IPNumInstReplaced,
-    "Number of instructions replaced with (simpler) instruction by IPSCCP");
-
-// Helper to check if \p LV is either a constant or a constant
-// range with a single element. This should cover exactly the same cases as the
-// old ValueLatticeElement::isConstant() and is intended to be used in the
-// transition to ValueLatticeElement.
-static bool isConstant(const ValueLatticeElement &LV) {
-  return LV.isConstant() ||
-         (LV.isConstantRange() && LV.getConstantRange().isSingleElement());
-}
-
-// Helper to check if \p LV is either overdefined or a constant range with more
-// than a single element. This should cover exactly the same cases as the old
-// ValueLatticeElement::isOverdefined() and is intended to be used in the
-// transition to ValueLatticeElement.
-static bool isOverdefined(const ValueLatticeElement &LV) {
-  return !LV.isUnknownOrUndef() && !isConstant(LV);
-}
-
-static bool canRemoveInstruction(Instruction *I) {
-  if (wouldInstructionBeTriviallyDead(I))
-    return true;
-
-  // Some instructions can be handled but are rejected above. Catch
-  // those cases by falling through to here.
-  // TODO: Mark globals as being constant earlier, so
-  // TODO: wouldInstructionBeTriviallyDead() knows that atomic loads
-  // TODO: are safe to remove.
-  return isa<LoadInst>(I);
-}
-
-static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
-  Constant *Const = nullptr;
-  if (V->getType()->isStructTy()) {
-    std::vector<ValueLatticeElement> IVs = Solver.getStructLatticeValueFor(V);
-    if (llvm::any_of(IVs, isOverdefined))
-      return false;
-    std::vector<Constant *> ConstVals;
-    auto *ST = cast<StructType>(V->getType());
-    for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
-      ValueLatticeElement V = IVs[i];
-      ConstVals.push_back(isConstant(V)
-                              ? Solver.getConstant(V)
-                              : UndefValue::get(ST->getElementType(i)));
-    }
-    Const = ConstantStruct::get(ST, ConstVals);
-  } else {
-    const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
-    if (isOverdefined(IV))
-      return false;
-
-    Const =
-        isConstant(IV) ? Solver.getConstant(IV) : UndefValue::get(V->getType());
-  }
-  assert(Const && "Constant is nullptr here!");
-
-  // Replacing `musttail` instructions with constant breaks `musttail` invariant
-  // unless the call itself can be removed.
-  // Calls with "clang.arc.attachedcall" implicitly use the return value and
-  // those uses cannot be updated with a constant.
-  CallBase *CB = dyn_cast<CallBase>(V);
-  if (CB && ((CB->isMustTailCall() &&
-              !canRemoveInstruction(CB)) ||
-             CB->getOperandBundle(LLVMContext::OB_clang_arc_attachedcall))) {
-    Function *F = CB->getCalledFunction();
-
-    // Don't zap returns of the callee
-    if (F)
-      Solver.addToMustPreserveReturnsInFunctions(F);
-
-    LLVM_DEBUG(dbgs() << "  Can\'t treat the result of call " << *CB
-                      << " as a constant\n");
-    return false;
-  }
-
-  LLVM_DEBUG(dbgs() << "  Constant: " << *Const << " = " << *V << '\n');
-
-  // Replaces all of the uses of a variable with uses of the constant.
-  V->replaceAllUsesWith(Const);
-  return true;
-}
-
-/// Try to replace signed instructions with their unsigned equivalent.
-static bool replaceSignedInst(SCCPSolver &Solver,
-                              SmallPtrSetImpl<Value *> &InsertedValues,
-                              Instruction &Inst) {
-  // Determine if a signed value is known to be >= 0.
-  auto isNonNegative = [&Solver](Value *V) {
-    // If this value was constant-folded, it may not have a solver entry.
-    // Handle integers. Otherwise, return false.
-    if (auto *C = dyn_cast<Constant>(V)) {
-      auto *CInt = dyn_cast<ConstantInt>(C);
-      return CInt && !CInt->isNegative();
-    }
-    const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
-    return IV.isConstantRange(/*UndefAllowed=*/false) &&
-           IV.getConstantRange().isAllNonNegative();
-  };
-
-  Instruction *NewInst = nullptr;
-  switch (Inst.getOpcode()) {
-  // Note: We do not fold sitofp -> uitofp here because that could be more
-  // expensive in codegen and may not be reversible in the backend.
-  case Instruction::SExt: {
-    // If the source value is not negative, this is a zext.
-    Value *Op0 = Inst.getOperand(0);
-    if (InsertedValues.count(Op0) || !isNonNegative(Op0))
-      return false;
-    NewInst = new ZExtInst(Op0, Inst.getType(), "", &Inst);
-    break;
-  }
-  case Instruction::AShr: {
-    // If the shifted value is not negative, this is a logical shift right.
-    Value *Op0 = Inst.getOperand(0);
-    if (InsertedValues.count(Op0) || !isNonNegative(Op0))
-      return false;
-    NewInst = BinaryOperator::CreateLShr(Op0, Inst.getOperand(1), "", &Inst);
-    break;
-  }
-  case Instruction::SDiv:
-  case Instruction::SRem: {
-    // If both operands are not negative, this is the same as udiv/urem.
-    Value *Op0 = Inst.getOperand(0), *Op1 = Inst.getOperand(1);
-    if (InsertedValues.count(Op0) || InsertedValues.count(Op1) ||
-        !isNonNegative(Op0) || !isNonNegative(Op1))
-      return false;
-    auto NewOpcode = Inst.getOpcode() == Instruction::SDiv ? Instruction::UDiv
-                                                           : Instruction::URem;
-    NewInst = BinaryOperator::Create(NewOpcode, Op0, Op1, "", &Inst);
-    break;
-  }
-  default:
-    return false;
-  }
-
-  // Wire up the new instruction and update state.
-  assert(NewInst && "Expected replacement instruction");
-  NewInst->takeName(&Inst);
-  InsertedValues.insert(NewInst);
-  Inst.replaceAllUsesWith(NewInst);
-  Solver.removeLatticeValueFor(&Inst);
-  Inst.eraseFromParent();
-  return true;
-}
-
-static bool simplifyInstsInBlock(SCCPSolver &Solver, BasicBlock &BB,
-                                 SmallPtrSetImpl<Value *> &InsertedValues,
-                                 Statistic &InstRemovedStat,
-                                 Statistic &InstReplacedStat) {
-  bool MadeChanges = false;
-  for (Instruction &Inst : make_early_inc_range(BB)) {
-    if (Inst.getType()->isVoidTy())
-      continue;
-    if (tryToReplaceWithConstant(Solver, &Inst)) {
-      if (canRemoveInstruction(&Inst))
-        Inst.eraseFromParent();
-
-      MadeChanges = true;
-      ++InstRemovedStat;
-    } else if (replaceSignedInst(Solver, InsertedValues, Inst)) {
-      MadeChanges = true;
-      ++InstReplacedStat;
-    }
-  }
-  return MadeChanges;
-}
-
-static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
-                                   DomTreeUpdater &DTU,
-                                   BasicBlock *&NewUnreachableBB);
-
 // runSCCP() - Run the Sparse Conditional Constant Propagation algorithm,
 // and return true if the function was modified.
 static bool runSCCP(Function &F, const DataLayout &DL,
                     const TargetLibraryInfo *TLI, DomTreeUpdater &DTU) {
   LLVM_DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n");
   SCCPSolver Solver(
       DL, [TLI](Function &F) -> const TargetLibraryInfo & { return *TLI; },
       F.getContext());
INITIALIZE_PASS_BEGIN(SCCPLegacyPass, "sccp",
                       "Sparse Conditional Constant Propagation", false, false)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 INITIALIZE_PASS_END(SCCPLegacyPass, "sccp",
                     "Sparse Conditional Constant Propagation", false, false)
 
 // createSCCPPass - This is the public interface to this file.
 FunctionPass *llvm::createSCCPPass() { return new SCCPLegacyPass(); }
 
-static void findReturnsToZap(Function &F,
-                             SmallVector<ReturnInst *, 8> &ReturnsToZap,
-                             SCCPSolver &Solver) {
-  // We can only do this if we know that nothing else can call the function.
-  if (!Solver.isArgumentTrackedFunction(&F))
-    return;
-
-  if (Solver.mustPreserveReturn(&F)) {
-    LLVM_DEBUG(
-        dbgs()
-        << "Can't zap returns of the function : " << F.getName()
-        << " due to present musttail or \"clang.arc.attachedcall\" call of "
-           "it\n");
-    return;
-  }
-
-  assert(
-      all_of(F.users(),
-             [&Solver](User *U) {
-               if (isa<Instruction>(U) &&
-                   !Solver.isBlockExecutable(cast<Instruction>(U)->getParent()))
-                 return true;
-               // Non-callsite uses are not impacted by zapping. Also, constant
-               // uses (like blockaddresses) could stuck around, without being
-               // used in the underlying IR, meaning we do not have lattice
-               // values for them.
-               if (!isa<CallBase>(U))
-                 return true;
-               if (U->getType()->isStructTy()) {
-                 return all_of(Solver.getStructLatticeValueFor(U),
-                               [](const ValueLatticeElement &LV) {
-                                 return !isOverdefined(LV);
-                               });
-               }
-               return !isOverdefined(Solver.getLatticeValueFor(U));
-             }) &&
-      "We can only zap functions where all live users have a concrete value");
-
-  for (BasicBlock &BB : F) {
-    if (CallInst *CI = BB.getTerminatingMustTailCall()) {
-      LLVM_DEBUG(dbgs() << "Can't zap return of the block due to present "
-                        << "musttail call : " << *CI << "\n");
-      (void)CI;
-      return;
-    }
-
-    if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator()))
-      if (!isa<UndefValue>(RI->getOperand(0)))
-        ReturnsToZap.push_back(RI);
-  }
-}
-
-static bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
-                                   DomTreeUpdater &DTU,
-                                   BasicBlock *&NewUnreachableBB) {
-  SmallPtrSet<BasicBlock *, 8> FeasibleSuccessors;
-  bool HasNonFeasibleEdges = false;
-  for (BasicBlock *Succ : successors(BB)) {
-    if (Solver.isEdgeFeasible(BB, Succ))
-      FeasibleSuccessors.insert(Succ);
-    else
-      HasNonFeasibleEdges = true;
-  }
-
-  // All edges feasible, nothing to do.
-  if (!HasNonFeasibleEdges)
-    return false;
-
-  // SCCP can only determine non-feasible edges for br, switch and indirectbr.
-  Instruction *TI = BB->getTerminator();
-  assert((isa<BranchInst>(TI) || isa<SwitchInst>(TI) ||
-          isa<IndirectBrInst>(TI)) &&
-         "Terminator must be a br, switch or indirectbr");
-
-  if (FeasibleSuccessors.size() == 0) {
-    // Branch on undef/poison, replace with unreachable.
-    SmallPtrSet<BasicBlock *, 8> SeenSuccs;
-    SmallVector<DominatorTree::UpdateType, 8> Updates;
-    for (BasicBlock *Succ : successors(BB)) {
-      Succ->removePredecessor(BB);
-      if (SeenSuccs.insert(Succ).second)
-        Updates.push_back({DominatorTree::Delete, BB, Succ});
-    }
-    TI->eraseFromParent();
-    new UnreachableInst(BB->getContext(), BB);
-    DTU.applyUpdatesPermissive(Updates);
-  } else if (FeasibleSuccessors.size() == 1) {
-    // Replace with an unconditional branch to the only feasible successor.
-    BasicBlock *OnlyFeasibleSuccessor = *FeasibleSuccessors.begin();
-    SmallVector<DominatorTree::UpdateType, 8> Updates;
-    bool HaveSeenOnlyFeasibleSuccessor = false;
-    for (BasicBlock *Succ : successors(BB)) {
-      if (Succ == OnlyFeasibleSuccessor && !HaveSeenOnlyFeasibleSuccessor) {
-        // Don't remove the edge to the only feasible successor the first time
-        // we see it. We still do need to remove any multi-edges to it though.
-        HaveSeenOnlyFeasibleSuccessor = true;
-        continue;
-      }
-
-      Succ->removePredecessor(BB);
-      Updates.push_back({DominatorTree::Delete, BB, Succ});
-    }
-
-    BranchInst::Create(OnlyFeasibleSuccessor, BB);
-    TI->eraseFromParent();
-    DTU.applyUpdatesPermissive(Updates);
-  } else if (FeasibleSuccessors.size() > 1) {
-    SwitchInstProfUpdateWrapper SI(*cast<SwitchInst>(TI));
-    SmallVector<DominatorTree::UpdateType, 8> Updates;
-
-    // If the default destination is unfeasible it will never be taken. Replace
-    // it with a new block with a single Unreachable instruction.
-    BasicBlock *DefaultDest = SI->getDefaultDest();
-    if (!FeasibleSuccessors.contains(DefaultDest)) {
-      if (!NewUnreachableBB) {
-        NewUnreachableBB =
-            BasicBlock::Create(DefaultDest->getContext(), "default.unreachable",
-                               DefaultDest->getParent(), DefaultDest);
-        new UnreachableInst(DefaultDest->getContext(), NewUnreachableBB);
-      }
-
-      SI->setDefaultDest(NewUnreachableBB);
-      Updates.push_back({DominatorTree::Delete, BB, DefaultDest});
-      Updates.push_back({DominatorTree::Insert, BB, NewUnreachableBB});
-    }
-
-    for (auto CI = SI->case_begin(); CI != SI->case_end();) {
-      if (FeasibleSuccessors.contains(CI->getCaseSuccessor())) {
-        ++CI;
-        continue;
-      }
-
-      BasicBlock *Succ = CI->getCaseSuccessor();
-      Succ->removePredecessor(BB);
-      Updates.push_back({DominatorTree::Delete, BB, Succ});
-      SI.removeCase(CI);
-      // Don't increment CI, as we removed a case.
-    }
-
-    DTU.applyUpdatesPermissive(Updates);
-  } else {
-    llvm_unreachable("Must have at least one feasible successor");
-  }
-  return true;
-}
-
-bool llvm::runIPSCCP(
-    Module &M, const DataLayout &DL,
-    std::function<const TargetLibraryInfo &(Function &)> GetTLI,
-    function_ref<AnalysisResultsForFn(Function &)> getAnalysis) {
-  SCCPSolver Solver(DL, GetTLI, M.getContext());
-
-  // Loop over all functions, marking arguments to those with their addresses
-  // taken or that are external as overdefined.
-  for (Function &F : M) {
-    if (F.isDeclaration())
-      continue;
-
-    Solver.addAnalysis(F, getAnalysis(F));
-
-    // Determine if we can track the function's return values. If so, add the
-    // function to the solver's set of return-tracked functions.
-    if (canTrackReturnsInterprocedurally(&F))
-      Solver.addTrackedFunction(&F);
-
-    // Determine if we can track the function's arguments. If so, add the
-    // function to the solver's set of argument-tracked functions.
-    if (canTrackArgumentsInterprocedurally(&F)) {
-      Solver.addArgumentTrackedFunction(&F);
-      continue;
-    }
-
-    // Assume the function is called.
-    Solver.markBlockExecutable(&F.front());
-
-    // Assume nothing about the incoming arguments.
-    for (Argument &AI : F.args())
-      Solver.markOverdefined(&AI);
-  }
-
-  // Determine if we can track any of the module's global variables. If so, add
-  // the global variables we can track to the solver's set of tracked global
-  // variables.
-  for (GlobalVariable &G : M.globals()) {
-    G.removeDeadConstantUsers();
-    if (canTrackGlobalVariableInterprocedurally(&G))
-      Solver.trackValueOfGlobalVariable(&G);
-  }
-
-  // Solve for constants.
-  bool ResolvedUndefs = true;
-  Solver.solve();
-  while (ResolvedUndefs) {
-    LLVM_DEBUG(dbgs() << "RESOLVING UNDEFS\n");
-    ResolvedUndefs = false;
-    for (Function &F : M) {
-      if (Solver.resolvedUndefsIn(F))
-        ResolvedUndefs = true;
-    }
-    if (ResolvedUndefs)
-      Solver.solve();
-  }
-
-  bool MadeChanges = false;
-
-  // Iterate over all of the instructions in the module, replacing them with
-  // constants if we have found them to be of constant values.
-
-  for (Function &F : M) {
-    if (F.isDeclaration())
-      continue;
-
-    SmallVector<BasicBlock *, 512> BlocksToErase;
-
-    if (Solver.isBlockExecutable(&F.front())) {
-      bool ReplacedPointerArg = false;
-      for (Argument &Arg : F.args()) {
-        if (!Arg.use_empty() && tryToReplaceWithConstant(Solver, &Arg)) {
-          ReplacedPointerArg |= Arg.getType()->isPointerTy();
-          ++IPNumArgsElimed;
-        }
-      }
-
-      // If we replaced an argument, we may now also access a global (currently
-      // classified as "other" memory). Update memory attribute to reflect this.
-      if (ReplacedPointerArg) {
-        auto UpdateAttrs = [&](AttributeList AL) {
-          MemoryEffects ME = AL.getMemoryEffects();
-          if (ME == MemoryEffects::unknown())
-            return AL;
-
-          ME |= MemoryEffects(MemoryEffects::Other,
-                              ME.getModRef(MemoryEffects::ArgMem));
-          return AL.addFnAttribute(
-              F.getContext(),
-              Attribute::getWithMemoryEffects(F.getContext(), ME));
-        };
-
-        F.setAttributes(UpdateAttrs(F.getAttributes()));
-        for (User *U : F.users()) {
-          auto *CB = dyn_cast<CallBase>(U);
-          if (!CB || CB->getCalledFunction() != &F)
-            continue;
-
-          CB->setAttributes(UpdateAttrs(CB->getAttributes()));
-        }
-      }
-      MadeChanges |= ReplacedPointerArg;
-    }
-
-    SmallPtrSet<Value *, 32> InsertedValues;
-    for (BasicBlock &BB : F) {
-      if (!Solver.isBlockExecutable(&BB)) {
-        LLVM_DEBUG(dbgs() << "  BasicBlock Dead:" << BB);
-        ++NumDeadBlocks;
-
-        MadeChanges = true;
-
-        if (&BB != &F.front())
-          BlocksToErase.push_back(&BB);
-        continue;
-      }
-
-      MadeChanges |= simplifyInstsInBlock(Solver, BB, InsertedValues,
-                                          IPNumInstRemoved, IPNumInstReplaced);
-    }
-
-    DomTreeUpdater DTU = Solver.getDTU(F);
-    // Change dead blocks to unreachable. We do it after replacing constants
-    // in all executable blocks, because changeToUnreachable may remove PHI
-    // nodes in executable blocks we found values for. The function's entry
-    // block is not part of BlocksToErase, so we have to handle it separately.
-    for (BasicBlock *BB : BlocksToErase) {
-      NumInstRemoved += changeToUnreachable(BB->getFirstNonPHI(),
-                                            /*PreserveLCSSA=*/false, &DTU);
-    }
-    if (!Solver.isBlockExecutable(&F.front()))
-      NumInstRemoved += changeToUnreachable(F.front().getFirstNonPHI(),
-                                            /*PreserveLCSSA=*/false, &DTU);
-
-    BasicBlock *NewUnreachableBB = nullptr;
-    for (BasicBlock &BB : F)
-      MadeChanges |= removeNonFeasibleEdges(Solver, &BB, DTU, NewUnreachableBB);
-
-    for (BasicBlock *DeadBB : BlocksToErase)
-      if (!DeadBB->hasAddressTaken())
-        DTU.deleteBB(DeadBB);
-
-    for (BasicBlock &BB : F) {
-      for (Instruction &Inst : llvm::make_early_inc_range(BB)) {
-        if (Solver.getPredicateInfoFor(&Inst)) {
-          if (auto *II = dyn_cast<IntrinsicInst>(&Inst)) {
-            if (II->getIntrinsicID() == Intrinsic::ssa_copy) {
-              Value *Op = II->getOperand(0);
-              Inst.replaceAllUsesWith(Op);
-              Inst.eraseFromParent();
-            }
-          }
-        }
-      }
-    }
-  }
-
-  // If we inferred constant or undef return values for a function, we replaced
-  // all call uses with the inferred value.  This means we don't need to bother
-  // actually returning anything from the function.  Replace all return
-  // instructions with return undef.
-  //
-  // Do this in two stages: first identify the functions we should process, then
-  // actually zap their returns.  This is important because we can only do this
-  // if the address of the function isn't taken.  In cases where a return is the
-  // last use of a function, the order of processing functions would affect
-  // whether other functions are optimizable.
-  SmallVector<ReturnInst*, 8> ReturnsToZap;
-
-  for (const auto &I : Solver.getTrackedRetVals()) {
-    Function *F = I.first;
-    const ValueLatticeElement &ReturnValue = I.second;
-
-    // If there is a known constant range for the return value, add !range
-    // metadata to the function's call sites.
-    if (ReturnValue.isConstantRange() &&
-        !ReturnValue.getConstantRange().isSingleElement()) {
-      // Do not add range metadata if the return value may include undef.
-      if (ReturnValue.isConstantRangeIncludingUndef())
-        continue;
-
-      auto &CR = ReturnValue.getConstantRange();
-      for (User *User : F->users()) {
-        auto *CB = dyn_cast<CallBase>(User);
-        if (!CB || CB->getCalledFunction() != F)
-          continue;
-
-        // Limit to cases where the return value is guaranteed to be neither
-        // poison nor undef. Poison will be outside any range and currently
-        // values outside of the specified range cause immediate undefined
-        // behavior.
-        if (!isGuaranteedNotToBeUndefOrPoison(CB, nullptr, CB))
-          continue;
-
-        // Do not touch existing metadata for now.
-        // TODO: We should be able to take the intersection of the existing
-        // metadata and the inferred range.
-        if (CB->getMetadata(LLVMContext::MD_range))
-          continue;
-
-        LLVMContext &Context = CB->getParent()->getContext();
-        Metadata *RangeMD[] = {
-            ConstantAsMetadata::get(ConstantInt::get(Context, CR.getLower())),
-            ConstantAsMetadata::get(ConstantInt::get(Context, CR.getUpper()))};
-        CB->setMetadata(LLVMContext::MD_range, MDNode::get(Context, RangeMD));
-      }
-      continue;
-    }
-    if (F->getReturnType()->isVoidTy())
-      continue;
-    if (isConstant(ReturnValue) || ReturnValue.isUnknownOrUndef())
-      findReturnsToZap(*F, ReturnsToZap, Solver);
-  }
-
-  for (auto *F : Solver.getMRVFunctionsTracked()) {
-    assert(F->getReturnType()->isStructTy() &&
-           "The return type should be a struct");
-    StructType *STy = cast<StructType>(F->getReturnType());
-    if (Solver.isStructLatticeConstant(F, STy))
-      findReturnsToZap(*F, ReturnsToZap, Solver);
-  }
-
-  // Zap all returns which we've identified as zap to change.
-  SmallSetVector<Function *, 8> FuncZappedReturn;
-  for (ReturnInst *RI : ReturnsToZap) {
-    Function *F = RI->getParent()->getParent();
-    RI->setOperand(0, UndefValue::get(F->getReturnType()));
-    // Record all functions that are zapped.
-    FuncZappedReturn.insert(F);
-  }
-
-  // Remove the returned attribute for zapped functions and the
-  // corresponding call sites.
-  for (Function *F : FuncZappedReturn) {
-    for (Argument &A : F->args())
-      F->removeParamAttr(A.getArgNo(), Attribute::Returned);
-    for (Use &U : F->uses()) {
-      // Skip over blockaddr users.
-      if (isa<BlockAddress>(U.getUser()))
-        continue;
-      CallBase *CB = cast<CallBase>(U.getUser());
-      for (Use &Arg : CB->args())
-        CB->removeParamAttr(CB->getArgOperandNo(&Arg), Attribute::Returned);
-    }
-  }
-
-  // If we inferred constant or undef values for globals variables, we can
-  // delete the global and any stores that remain to it.
-  for (const auto &I : make_early_inc_range(Solver.getTrackedGlobals())) {
-    GlobalVariable *GV = I.first;
-    if (isOverdefined(I.second))
-      continue;
-    LLVM_DEBUG(dbgs() << "Found that GV '" << GV->getName()
-                      << "' is constant!\n");
-    while (!GV->use_empty()) {
-      StoreInst *SI = cast<StoreInst>(GV->user_back());
-      SI->eraseFromParent();
-      MadeChanges = true;
-    }
-    M.getGlobalList().erase(GV);
-    ++IPNumGlobalConst;
-  }
-
-  return MadeChanges;
-}

llvm/lib/Transforms/Utils/SCCPSolver.cpp

 // utility.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/SCCPSolver.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/ValueLattice.h"
+#include "llvm/Analysis/ValueLatticeUtils.h"
 #include "llvm/IR/InstVisitor.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include <cassert>
 #include <utility>
 #include <vector>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "sccp"
 
 // The maximum number of range extensions allowed for operations requiring
 // widening.
 static const unsigned MaxNumRangeExtensions = 10;
 
 /// Returns MergeOptions with MaxWidenSteps set to MaxNumRangeExtensions.
 static ValueLatticeElement::MergeOptions getMaxWidenStepsOpts() {
   return ValueLatticeElement::MergeOptions().setMaxWidenSteps(
       MaxNumRangeExtensions);
 }
 
-namespace {
+namespace llvm {
 
 // Helper to check if \p LV is either a constant or a constant
 // range with a single element. This should cover exactly the same cases as the
 // old ValueLatticeElement::isConstant() and is intended to be used in the
 // transition to ValueLatticeElement.
 bool isConstant(const ValueLatticeElement &LV) {
   return LV.isConstant() ||
          (LV.isConstantRange() && LV.getConstantRange().isSingleElement());
 }
 
 // Helper to check if \p LV is either overdefined or a constant range with more
 // than a single element. This should cover exactly the same cases as the old
 // ValueLatticeElement::isOverdefined() and is intended to be used in the
 // transition to ValueLatticeElement.
 bool isOverdefined(const ValueLatticeElement &LV) {
   return !LV.isUnknownOrUndef() && !isConstant(LV);
 }
 
-} // namespace
+static bool canRemoveInstruction(Instruction *I) {
+  if (wouldInstructionBeTriviallyDead(I))
+    return true;
 
-namespace llvm {
+  // Some instructions can be handled but are rejected above. Catch
+  // those cases by falling through to here.
+  // TODO: Mark globals as being constant earlier, so
+  // TODO: wouldInstructionBeTriviallyDead() knows that atomic loads
+  // TODO: are safe to remove.
+  return isa<LoadInst>(I);
+}
+
+bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
+  Constant *Const = nullptr;
+  if (V->getType()->isStructTy()) {
+    std::vector<ValueLatticeElement> IVs = Solver.getStructLatticeValueFor(V);
+    if (llvm::any_of(IVs, isOverdefined))
+      return false;
+    std::vector<Constant *> ConstVals;
+    auto *ST = cast<StructType>(V->getType());
+    for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
+      ValueLatticeElement V = IVs[i];
+      ConstVals.push_back(isConstant(V)
+                              ? Solver.getConstant(V)
+                              : UndefValue::get(ST->getElementType(i)));
+    }
+    Const = ConstantStruct::get(ST, ConstVals);
+  } else {
+    const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
+    if (isOverdefined(IV))
+      return false;
+
+    Const =
+        isConstant(IV) ? Solver.getConstant(IV) : UndefValue::get(V->getType());
+  }
+  assert(Const && "Constant is nullptr here!");
+
+  // Replacing `musttail` instructions with constant breaks `musttail` invariant
+  // unless the call itself can be removed.
+  // Calls with "clang.arc.attachedcall" implicitly use the return value and
+  // those uses cannot be updated with a constant.
+  CallBase *CB = dyn_cast<CallBase>(V);
+  if (CB && ((CB->isMustTailCall() &&
+              !canRemoveInstruction(CB)) ||
+             CB->getOperandBundle(LLVMContext::OB_clang_arc_attachedcall))) {
+    Function *F = CB->getCalledFunction();
+
+    // Don't zap returns of the callee
+    if (F)
+      Solver.addToMustPreserveReturnsInFunctions(F);
+
+    LLVM_DEBUG(dbgs() << "  Can\'t treat the result of call " << *CB
+                      << " as a constant\n");
+    return false;
+  }
+
+  LLVM_DEBUG(dbgs() << "  Constant: " << *Const << " = " << *V << '\n');
+
+  // Replaces all of the uses of a variable with uses of the constant.
+  V->replaceAllUsesWith(Const);
+  return true;
+}
+
+/// Try to replace signed instructions with their unsigned equivalent.
+static bool replaceSignedInst(SCCPSolver &Solver,
+                              SmallPtrSetImpl<Value *> &InsertedValues,
+                              Instruction &Inst) {
+  // Determine if a signed value is known to be >= 0.
+  auto isNonNegative = [&Solver](Value *V) {
+    // If this value was constant-folded, it may not have a solver entry.
+    // Handle integers. Otherwise, return false.
+    if (auto *C = dyn_cast<Constant>(V)) {
+      auto *CInt = dyn_cast<ConstantInt>(C);
+      return CInt && !CInt->isNegative();
+    }
+    const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
+    return IV.isConstantRange(/*UndefAllowed=*/false) &&
+           IV.getConstantRange().isAllNonNegative();
+  };
+
+  Instruction *NewInst = nullptr;
+  switch (Inst.getOpcode()) {
+  // Note: We do not fold sitofp -> uitofp here because that could be more
+  // expensive in codegen and may not be reversible in the backend.
+  case Instruction::SExt: {
+    // If the source value is not negative, this is a zext.
+    Value *Op0 = Inst.getOperand(0);
+    if (InsertedValues.count(Op0) || !isNonNegative(Op0))
+      return false;
+    NewInst = new ZExtInst(Op0, Inst.getType(), "", &Inst);
+    break;
+  }
+  case Instruction::AShr: {
+    // If the shifted value is not negative, this is a logical shift right.
+    Value *Op0 = Inst.getOperand(0);
+    if (InsertedValues.count(Op0) || !isNonNegative(Op0))
+      return false;
+    NewInst = BinaryOperator::CreateLShr(Op0, Inst.getOperand(1), "", &Inst);
+    break;
+  }
+  case Instruction::SDiv:
+  case Instruction::SRem: {
+    // If both operands are not negative, this is the same as udiv/urem.
+    Value *Op0 = Inst.getOperand(0), *Op1 = Inst.getOperand(1);
+    if (InsertedValues.count(Op0) || InsertedValues.count(Op1) ||
+        !isNonNegative(Op0) || !isNonNegative(Op1))
+      return false;
+    auto NewOpcode = Inst.getOpcode() == Instruction::SDiv ? Instruction::UDiv
+                                                           : Instruction::URem;
+    NewInst = BinaryOperator::Create(NewOpcode, Op0, Op1, "", &Inst);
+    break;
+  }
+  default:
+    return false;
+  }
+
+  // Wire up the new instruction and update state.
+  assert(NewInst && "Expected replacement instruction");
+  NewInst->takeName(&Inst);
+  InsertedValues.insert(NewInst);
+  Inst.replaceAllUsesWith(NewInst);
+  Solver.removeLatticeValueFor(&Inst);
+  Inst.eraseFromParent();
+  return true;
+}
+
+bool simplifyInstsInBlock(SCCPSolver &Solver, BasicBlock &BB,
+                          SmallPtrSetImpl<Value *> &InsertedValues,
+                          Statistic &InstRemovedStat,
+                          Statistic &InstReplacedStat) {
+  bool MadeChanges = false;
+  for (Instruction &Inst : make_early_inc_range(BB)) {
+    if (Inst.getType()->isVoidTy())
+      continue;
+    if (tryToReplaceWithConstant(Solver, &Inst)) {
+      if (canRemoveInstruction(&Inst))
+        Inst.eraseFromParent();
+
+      MadeChanges = true;
+      ++InstRemovedStat;
+    } else if (replaceSignedInst(Solver, InsertedValues, Inst)) {
+      MadeChanges = true;
+      ++InstReplacedStat;
+    }
+  }
+  return MadeChanges;
+}
+
+bool removeNonFeasibleEdges(const SCCPSolver &Solver, BasicBlock *BB,
+                            DomTreeUpdater &DTU,
+                            BasicBlock *&NewUnreachableBB) {
+  SmallPtrSet<BasicBlock *, 8> FeasibleSuccessors;
+  bool HasNonFeasibleEdges = false;
+  for (BasicBlock *Succ : successors(BB)) {
+    if (Solver.isEdgeFeasible(BB, Succ))
+      FeasibleSuccessors.insert(Succ);
+    else
+      HasNonFeasibleEdges = true;
+  }
+
+  // All edges feasible, nothing to do.
+  if (!HasNonFeasibleEdges)
+    return false;
+
+  // SCCP can only determine non-feasible edges for br, switch and indirectbr.
+  Instruction *TI = BB->getTerminator();
+  assert((isa<BranchInst>(TI) || isa<SwitchInst>(TI) ||
+          isa<IndirectBrInst>(TI)) &&
+         "Terminator must be a br, switch or indirectbr");
+
+  if (FeasibleSuccessors.size() == 0) {
+    // Branch on undef/poison, replace with unreachable.
+    SmallPtrSet<BasicBlock *, 8> SeenSuccs;
+    SmallVector<DominatorTree::UpdateType, 8> Updates;
+    for (BasicBlock *Succ : successors(BB)) {
+      Succ->removePredecessor(BB);
+      if (SeenSuccs.insert(Succ).second)
+        Updates.push_back({DominatorTree::Delete, BB, Succ});
+    }
+    TI->eraseFromParent();
+    new UnreachableInst(BB->getContext(), BB);
+    DTU.applyUpdatesPermissive(Updates);
+  } else if (FeasibleSuccessors.size() == 1) {
+    // Replace with an unconditional branch to the only feasible successor.
+    BasicBlock *OnlyFeasibleSuccessor = *FeasibleSuccessors.begin();
+    SmallVector<DominatorTree::UpdateType, 8> Updates;
+    bool HaveSeenOnlyFeasibleSuccessor = false;
+    for (BasicBlock *Succ : successors(BB)) {
+      if (Succ == OnlyFeasibleSuccessor && !HaveSeenOnlyFeasibleSuccessor) {
+        // Don't remove the edge to the only feasible successor the first time
+        // we see it. We still do need to remove any multi-edges to it though.
+        HaveSeenOnlyFeasibleSuccessor = true;
+        continue;
+      }
+
+      Succ->removePredecessor(BB);
+      Updates.push_back({DominatorTree::Delete, BB, Succ});
+    }
+
+    BranchInst::Create(OnlyFeasibleSuccessor, BB);
+    TI->eraseFromParent();
+    DTU.applyUpdatesPermissive(Updates);
+  } else if (FeasibleSuccessors.size() > 1) {
+    SwitchInstProfUpdateWrapper SI(*cast<SwitchInst>(TI));
+    SmallVector<DominatorTree::UpdateType, 8> Updates;
+
+    // If the default destination is unfeasible it will never be taken. Replace
+    // it with a new block with a single Unreachable instruction.
+    BasicBlock *DefaultDest = SI->getDefaultDest();
+    if (!FeasibleSuccessors.contains(DefaultDest)) {
+      if (!NewUnreachableBB) {
+        NewUnreachableBB =
+            BasicBlock::Create(DefaultDest->getContext(), "default.unreachable",
+                               DefaultDest->getParent(), DefaultDest);
+        new UnreachableInst(DefaultDest->getContext(), NewUnreachableBB);
+      }
+
+      SI->setDefaultDest(NewUnreachableBB);
+      Updates.push_back({DominatorTree::Delete, BB, DefaultDest});
+      Updates.push_back({DominatorTree::Insert, BB, NewUnreachableBB});
+    }
+
+    for (auto CI = SI->case_begin(); CI != SI->case_end();) {
+      if (FeasibleSuccessors.contains(CI->getCaseSuccessor())) {
+        ++CI;
+        continue;
+      }
+
+      BasicBlock *Succ = CI->getCaseSuccessor();
+      Succ->removePredecessor(BB);
+      Updates.push_back({DominatorTree::Delete, BB, Succ});
+      SI.removeCase(CI);
+      // Don't increment CI, as we removed a case.
+    }
+
+    DTU.applyUpdatesPermissive(Updates);
+  } else {
+    llvm_unreachable("Must have at least one feasible successor");
+  }
+  return true;
+}
 
 /// Helper class for SCCPSolver. This implements the instruction visitor and
 /// holds all the state.
 class SCCPInstVisitor : public InstVisitor<SCCPInstVisitor> {
   const DataLayout &DL;
   std::function<const TargetLibraryInfo &(Function &)> GetTLI;
   SmallPtrSet<BasicBlock *, 8> BBExecutable; // The BBs that are executable.
   DenseMap<Value *, ValueLatticeElement>

llvm/utils/gn/secondary/llvm/lib/Transforms/IPO/BUILD.gn

 static_library("IPO") {
   output_name = "LLVMipo"
   deps = [
     "//llvm/lib/Analysis",
     "//llvm/lib/Bitcode/Reader",
     "//llvm/lib/Bitcode/Writer",
     "//llvm/lib/Frontend/OpenMP",
     "//llvm/lib/IR",
     "//llvm/lib/IRReader",
     "//llvm/lib/Linker",
     "//llvm/lib/Object",
     "//llvm/lib/ProfileData",
     "//llvm/lib/Support",
     "//llvm/lib/Transforms/AggressiveInstCombine",
     "//llvm/lib/Transforms/InstCombine",
     "//llvm/lib/Transforms/Instrumentation",
-    "//llvm/lib/Transforms/Scalar",
     "//llvm/lib/Transforms/Utils",
     "//llvm/lib/Transforms/Vectorize",
   ]
   sources = [
     "AlwaysInliner.cpp",
     "Annotation2Metadata.cpp",
     "ArgumentPromotion.cpp",
     "Attributor.cpp",