[llvm] r245762 - Improve the determinism of MergeFunctions

Mehdi Amini via llvm-commits llvm-commits at lists.llvm.org
Sat Aug 22 17:32:05 PDT 2015


Hi,


> On Aug 21, 2015, at 4:27 PM, JF Bastien via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: jfb
> Date: Fri Aug 21 18:27:24 2015
> New Revision: 245762
> 
> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D245762-26view-3Drev&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=v-ruWq0KCv2O3thJZiK6naxuXK8mQHZUmGq5FBtAmZ4&m=8AXWbmpresvhRsDs49PoX5gvb_41wieiXuHyjTJ5YMo&s=FoM7SY1rz3BRnUS5DPo6KV91Zjpw7DxGgcFb8AWousg&e= 
> Log:
> Improve the determinism of MergeFunctions
> 
> Summary:
> 
> Merge functions previously relied on unsigned comparisons of pointer values to
> order functions. This caused observable non-determinism in the compiler for
> large bitcode programs. Basically, opt -mergefuncs program.bc | md5sum produces
> different hashes when run repeatedly on the same machine. Differing output was
> observed on three large bitcodes, but it was less frequent on the smallest file.
> It is possible that this only manifests on the large inputs, hence remaining
> undetected until now.
> 
> This patch fixes this by removing (almost, see below) all places where
> comparisons between pointers are used to order functions. Most of these changes
> are local, but the comparison of global values requires assigning an identifier
> to each local in the order it is visited. This is very similar to the way the
> comparison function identifies Value*'s defined within a function. Because the
> order of visiting the functions and their subparts is deterministic, the
> identifiers assigned to the globals will be as well, and the order of functions
> will be deterministic.
> 
> With these changes, there is no more observed non-determinism. There is also
> only minor slowdowns (negligible to 4%) compared to the baseline, which is
> likely a result of the fact that global comparisons involve hash lookups and not
> just pointer comparisons.
> 
> The one caveat so far is that programs containing BlockAddress constants can
> still be non-deterministic. It is not clear what the right solution is here. In
> particular, even if the global numbers are used to order by function, we still
> need a way to order the BasicBlock*'s. Unfortunately, we cannot just bail out
> and fail to order the functions or consider them equal, because we require a
> total order over functions. Note that programs with BlockAddress constants are
> relatively rare, so the impact of leaving this in is minor as long as this pass
> is opt-in.
> 
> Author: jrkoenig
> 
> Reviewers: nlewycky, jfb, dschuff
> 
> Subscribers: jevinskie, llvm-commits, chapuni
> 
> Differential revision: https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D12168&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=v-ruWq0KCv2O3thJZiK6naxuXK8mQHZUmGq5FBtAmZ4&m=8AXWbmpresvhRsDs49PoX5gvb_41wieiXuHyjTJ5YMo&s=p-0b5PAhXedHTFOoxIbiG0nruh9yDWiUogCym25HyvQ&e= 
> 
> Added:
>    llvm/trunk/test/Transforms/MergeFunc/constant-entire-value.ll
> Modified:
>    llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
> 
> Modified: llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_Transforms_IPO_MergeFunctions.cpp-3Frev-3D245762-26r1-3D245761-26r2-3D245762-26view-3Ddiff&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=v-ruWq0KCv2O3thJZiK6naxuXK8mQHZUmGq5FBtAmZ4&m=8AXWbmpresvhRsDs49PoX5gvb_41wieiXuHyjTJ5YMo&s=mdhMReHM3LfubUScGkXKDBloDc16X-lxEn4f_KZhc6Y&e= 
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp Fri Aug 21 18:27:24 2015
> @@ -106,6 +106,7 @@
> #include "llvm/IR/Module.h"
> #include "llvm/IR/Operator.h"
> #include "llvm/IR/ValueHandle.h"
> +#include "llvm/IR/ValueMap.h"
> #include "llvm/Pass.h"
> #include "llvm/Support/CommandLine.h"
> #include "llvm/Support/Debug.h"
> @@ -130,14 +131,50 @@ static cl::opt<unsigned> NumFunctionsFor
> 
> namespace {
> 
> +/// GlobalNumberState assigns an integer to each global value in the program,
> +/// which is used by the comparison routine to order references to globals. This
> +/// state must be preserved throughout the pass, because Functions and other
> +/// globals need to maintain their relative order. Globals are assigned a number
> +/// when they are first visited. This order is deterministic, and so the
> +/// assigned numbers are as well. When two functions are merged, neither number
> +/// is updated. If the symbols are weak, this would be incorrect. If they are
> +/// strong, then one will be replaced at all references to the other, and so
> +/// direct callsites will now see one or the other symbol, and no update is
> +/// necessary. Note that if we were guaranteed unique names, we could just
> +/// compare those, but this would not work for stripped bitcodes or for those
> +/// few symbols without a name.
> +class GlobalNumberState {
> +  struct Config : ValueMapConfig<GlobalValue*> {
> +    enum { FollowRAUW = false };
> +  };
> +  // Each GlobalValue is mapped to an identifier. The Config ensures when RAUW
> +  // occurs, the mapping does not change. Tracking changes is unnecessary, and
> +  // also problematic for weak symbols (which may be overwritten).
> +  typedef ValueMap<GlobalValue *, uint64_t, Config> ValueNumberMap;
> +  ValueNumberMap GlobalNumbers;
> +  // The next unused serial number to assign to a global.
> +  uint64_t NextNumber;
> +  public:
> +    GlobalNumberState() : GlobalNumbers(), NextNumber(0) {}
> +    uint64_t getNumber(GlobalValue* Global) {
> +      ValueNumberMap::iterator MapIter;
> +      bool Inserted;
> +      std::tie(MapIter, Inserted) = GlobalNumbers.insert({Global, NextNumber});
> +      if (Inserted)
> +        NextNumber++;
> +      return MapIter->second;
> +    }
> +};
> +
> /// FunctionComparator - Compares two functions to determine whether or not
> /// they will generate machine code with the same behaviour. DataLayout is
> /// used if available. The comparator always fails conservatively (erring on the
> /// side of claiming that two functions are different).
> class FunctionComparator {
> public:
> -  FunctionComparator(const Function *F1, const Function *F2)
> -      : FnL(F1), FnR(F2) {}
> +  FunctionComparator(const Function *F1, const Function *F2,
> +                     GlobalNumberState* GN)
> +      : FnL(F1), FnR(F2), GlobalNumbers(GN) {}
> 
>   /// Test whether the two functions have equivalent behaviour.
>   int compare();
> @@ -148,7 +185,7 @@ public:
> 
> private:
>   /// Test whether two basic blocks have equivalent behaviour.
> -  int compare(const BasicBlock *BBL, const BasicBlock *BBR);
> +  int cmpBasicBlocks(const BasicBlock *BBL, const BasicBlock *BBR);
> 
>   /// Constants comparison.
>   /// Its analog to lexicographical comparison between hypothetical numbers
> @@ -254,6 +291,10 @@ private:
>   /// If these properties are equal - compare their contents.
>   int cmpConstants(const Constant *L, const Constant *R);
> 
> +  /// Compares two global values by number. Uses the GlobalNumbersState to
> +  /// identify the same gobals across function calls.
> +  int cmpGlobalValues(GlobalValue *L, GlobalValue *R);
> +
>   /// Assign or look up previously assigned numbers for the two values, and
>   /// return whether the numbers are equal. Numbers are assigned in the order
>   /// visited.
> @@ -333,8 +374,9 @@ private:
>   ///
>   /// 1. If types are of different kind (different type IDs).
>   ///    Return result of type IDs comparison, treating them as numbers.
> -  /// 2. If types are vectors or integers, compare Type* values as numbers.
> -  /// 3. Types has same ID, so check whether they belongs to the next group:
> +  /// 2. If types are integers, check that they have the same width. If they
> +  /// are vectors, check that they have the same count and subtype.
> +  /// 3. Types have the same ID, so check whether they are one of:
>   /// * Void
>   /// * Float
>   /// * Double
> @@ -343,8 +385,7 @@ private:
>   /// * PPC_FP128
>   /// * Label
>   /// * Metadata
> -  /// If so - return 0, yes - we can treat these types as equal only because
> -  /// their IDs are same.
> +  /// We can treat these types as equal whenever their IDs are same.
>   /// 4. If Left and Right are pointers, return result of address space
>   /// comparison (numbers comparison). We can treat pointer types of same
>   /// address space as equal.
> @@ -359,7 +400,8 @@ private:
> 
>   int cmpAPInts(const APInt &L, const APInt &R) const;
>   int cmpAPFloats(const APFloat &L, const APFloat &R) const;
> -  int cmpStrings(StringRef L, StringRef R) const;
> +  int cmpInlineAsm(const InlineAsm *L, const InlineAsm *R) const;
> +  int cmpMem(StringRef L, StringRef R) const;
>   int cmpAttrs(const AttributeSet L, const AttributeSet R) const;
> 
>   // The two functions undergoing comparison.
> @@ -399,33 +441,28 @@ private:
>   /// could be operands from further BBs we didn't scan yet.
>   /// So it's impossible to use dominance properties in general.
>   DenseMap<const Value*, int> sn_mapL, sn_mapR;
> +
> +  // The global state we will use
> +  GlobalNumberState* GlobalNumbers;
> };
> 
> class FunctionNode {
>   mutable AssertingVH<Function> F;
>   FunctionComparator::FunctionHash Hash;
> -
> public:
>   // Note the hash is recalculated potentially multiple times, but it is cheap.
> -  FunctionNode(Function *F) : F(F), Hash(FunctionComparator::functionHash(*F)){}
> +  FunctionNode(Function *F)
> +    : F(F), Hash(FunctionComparator::functionHash(*F))  {}
>   Function *getFunc() const { return F; }
> +  FunctionComparator::FunctionHash getHash() const { return Hash; }
> 
>   /// Replace the reference to the function F by the function G, assuming their
>   /// implementations are equal.
>   void replaceBy(Function *G) const {
> -    assert(!(*this < FunctionNode(G)) && !(FunctionNode(G) < *this) &&
> -           "The two functions must be equal");
> -
>     F = G;
>   }
> 
>   void release() { F = 0; }
> -  bool operator<(const FunctionNode &RHS) const {
> -    // Order first by hashes, then full function comparison.
> -    if (Hash != RHS.Hash)
> -      return Hash < RHS.Hash;
> -    return (FunctionComparator(F, RHS.getFunc()).compare()) == -1;
> -  }
> };
> }
> 
> @@ -444,13 +481,17 @@ int FunctionComparator::cmpAPInts(const
> }
> 
> int FunctionComparator::cmpAPFloats(const APFloat &L, const APFloat &R) const {
> -  if (int Res = cmpNumbers((uint64_t)&L.getSemantics(),
> -                           (uint64_t)&R.getSemantics()))
> +  // TODO: This correctly handles all existing fltSemantics, because they all
> +  // have different precisions. This isn't very robust, however, if new types
> +  // with different exponent ranges are introduced.
> +  const fltSemantics &SL = L.getSemantics(), &SR = R.getSemantics();
> +  if (int Res = cmpNumbers(APFloat::semanticsPrecision(SL),
> +                           APFloat::semanticsPrecision(SR)))
>     return Res;
>   return cmpAPInts(L.bitcastToAPInt(), R.bitcastToAPInt());
> }
> 
> -int FunctionComparator::cmpStrings(StringRef L, StringRef R) const {
> +int FunctionComparator::cmpMem(StringRef L, StringRef R) const {
>   // Prevent heavy comparison, compare sizes first.
>   if (int Res = cmpNumbers(L.size(), R.size()))
>     return Res;
> @@ -556,9 +597,25 @@ int FunctionComparator::cmpConstants(con
>   if (!L->isNullValue() && R->isNullValue())
>     return -1;
> 
> +  auto GlobalValueL = const_cast<GlobalValue*>(dyn_cast<GlobalValue>(L));
> +  auto GlobalValueR = const_cast<GlobalValue*>(dyn_cast<GlobalValue>(R));
> +  if (GlobalValueL && GlobalValueR) {
> +    return cmpGlobalValues(GlobalValueL, GlobalValueR);
> +  }
> +
>   if (int Res = cmpNumbers(L->getValueID(), R->getValueID()))
>     return Res;
> 
> +  if (const auto *SeqL = dyn_cast<ConstantDataSequential>(L)) {
> +    const auto *SeqR = dyn_cast<ConstantDataSequential>(R);
> +    // This handles ConstantDataArray and ConstantDataVector. Note that we
> +    // compare the two raw data arrays, which might differ depending on the host
> +    // endianness. This isn't a problem though, because the endiness of a module
> +    // will affect the order of the constants, but this order is the same
> +    // for a given input module and host platform.
> +    return cmpMem(SeqL->getRawDataValues(), SeqR->getRawDataValues());


You are dereferencing SeqR after a dyn_cast<>. There is something fishy here.
Can you have a look?

Thanks,

Mehdi



> +  }
> +
>   switch (L->getValueID()) {
>   case Value::UndefValueVal: return TypesRes;
>   case Value::ConstantIntVal: {
> @@ -627,12 +684,21 @@ int FunctionComparator::cmpConstants(con
>     }
>     return 0;
>   }
> -  case Value::FunctionVal:
> -  case Value::GlobalVariableVal:
> -  case Value::GlobalAliasVal:
> -  default: // Unknown constant, cast L and R pointers to numbers and compare.
> +  case Value::BlockAddressVal: {
> +    // FIXME: This still uses a pointer comparison. It isn't clear how to remove
> +    // this. This only affects programs which take BlockAddresses and store them
> +    // as constants, which is limited to interepreters, etc.
>     return cmpNumbers((uint64_t)L, (uint64_t)R);
>   }
> +  default: // Unknown constant, abort.
> +    DEBUG(dbgs() << "Looking at valueID " << L->getValueID() << "\n");
> +    llvm_unreachable("Constant ValueID not recognized.");
> +    return -1;
> +  }
> +}
> +
> +int FunctionComparator::cmpGlobalValues(GlobalValue *L, GlobalValue* R) {
> +  return cmpNumbers(GlobalNumbers->getNumber(L), GlobalNumbers->getNumber(R));
> }
> 
> /// cmpType - compares two types,
> @@ -660,10 +726,15 @@ int FunctionComparator::cmpTypes(Type *T
>     llvm_unreachable("Unknown type!");
>     // Fall through in Release mode.
>   case Type::IntegerTyID:
> -  case Type::VectorTyID:
> -    // TyL == TyR would have returned true earlier.
> -    return cmpNumbers((uint64_t)TyL, (uint64_t)TyR);
> -
> +    return cmpNumbers(cast<IntegerType>(TyL)->getBitWidth(),
> +                      cast<IntegerType>(TyR)->getBitWidth());
> +  case Type::VectorTyID: {
> +    VectorType *VTyL = cast<VectorType>(TyL), *VTyR = cast<VectorType>(TyR);
> +    if (int Res = cmpNumbers(VTyL->getNumElements(), VTyR->getNumElements()))
> +      return Res;
> +    return cmpTypes(VTyL->getElementType(), VTyR->getElementType());
> +  }
> +  // TyL == TyR would have returned true earlier, because types are uniqued.
>   case Type::VoidTyID:
>   case Type::FloatTyID:
>   case Type::DoubleTyID:
> @@ -895,9 +966,8 @@ int FunctionComparator::cmpGEPs(const GE
>   if (GEPL->accumulateConstantOffset(DL, OffsetL) &&
>       GEPR->accumulateConstantOffset(DL, OffsetR))
>     return cmpAPInts(OffsetL, OffsetR);
> -
> -  if (int Res = cmpNumbers((uint64_t)GEPL->getPointerOperand()->getType(),
> -                           (uint64_t)GEPR->getPointerOperand()->getType()))
> +  if (int Res = cmpTypes(GEPL->getPointerOperand()->getType(),
> +                         GEPR->getPointerOperand()->getType()))
>     return Res;
> 
>   if (int Res = cmpNumbers(GEPL->getNumOperands(), GEPR->getNumOperands()))
> @@ -911,6 +981,28 @@ int FunctionComparator::cmpGEPs(const GE
>   return 0;
> }
> 
> +int FunctionComparator::cmpInlineAsm(const InlineAsm *L,
> +                                     const InlineAsm *R) const {
> +  // InlineAsm's are uniqued. If they are the same pointer, obviously they are
> +  // the same, otherwise compare the fields.
> +  if (L == R)
> +    return 0;
> +  if (int Res = cmpTypes(L->getFunctionType(), R->getFunctionType()))
> +    return Res;
> +  if (int Res = cmpMem(L->getAsmString(), R->getAsmString()))
> +    return Res;
> +  if (int Res = cmpMem(L->getConstraintString(), R->getConstraintString()))
> +    return Res;
> +  if (int Res = cmpNumbers(L->hasSideEffects(), R->hasSideEffects()))
> +    return Res;
> +  if (int Res = cmpNumbers(L->isAlignStack(), R->isAlignStack()))
> +    return Res;
> +  if (int Res = cmpNumbers(L->getDialect(), R->getDialect()))
> +    return Res;
> +  llvm_unreachable("InlineAsm blocks were not uniqued.");
> +  return 0;
> +}
> +
> /// Compare two values used by the two functions under pair-wise comparison. If
> /// this is the first time the values are seen, they're added to the mapping so
> /// that we will detect mismatches on next use.
> @@ -945,7 +1037,7 @@ int FunctionComparator::cmpValues(const
>   const InlineAsm *InlineAsmR = dyn_cast<InlineAsm>(R);
> 
>   if (InlineAsmL && InlineAsmR)
> -    return cmpNumbers((uint64_t)L, (uint64_t)R);
> +    return cmpInlineAsm(InlineAsmL, InlineAsmR);
>   if (InlineAsmL)
>     return 1;
>   if (InlineAsmR)
> @@ -957,7 +1049,8 @@ int FunctionComparator::cmpValues(const
>   return cmpNumbers(LeftSN.first->second, RightSN.first->second);
> }
> // Test whether two basic blocks have equivalent behaviour.
> -int FunctionComparator::compare(const BasicBlock *BBL, const BasicBlock *BBR) {
> +int FunctionComparator::cmpBasicBlocks(const BasicBlock *BBL,
> +                                       const BasicBlock *BBR) {
>   BasicBlock::const_iterator InstL = BBL->begin(), InstLE = BBL->end();
>   BasicBlock::const_iterator InstR = BBR->begin(), InstRE = BBR->end();
> 
> @@ -1020,7 +1113,7 @@ int FunctionComparator::compare() {
>     return Res;
> 
>   if (FnL->hasGC()) {
> -    if (int Res = cmpNumbers((uint64_t)FnL->getGC(), (uint64_t)FnR->getGC()))
> +    if (int Res = cmpMem(FnL->getGC(), FnR->getGC()))
>       return Res;
>   }
> 
> @@ -1028,7 +1121,7 @@ int FunctionComparator::compare() {
>     return Res;
> 
>   if (FnL->hasSection()) {
> -    if (int Res = cmpStrings(FnL->getSection(), FnR->getSection()))
> +    if (int Res = cmpMem(FnL->getSection(), FnR->getSection()))
>       return Res;
>   }
> 
> @@ -1074,7 +1167,7 @@ int FunctionComparator::compare() {
>     if (int Res = cmpValues(BBL, BBR))
>       return Res;
> 
> -    if (int Res = compare(BBL, BBR))
> +    if (int Res = cmpBasicBlocks(BBL, BBR))
>       return Res;
> 
>     const TerminatorInst *TermL = BBL->getTerminator();
> @@ -1129,7 +1222,7 @@ FunctionComparator::FunctionHash Functio
>   SmallVector<const BasicBlock *, 8> BBs;
>   SmallSet<const BasicBlock *, 16> VisitedBBs;
> 
> -  // Walk the blocks in the same order as FunctionComparator::compare(),
> +  // Walk the blocks in the same order as FunctionComparator::cmpBasicBlocks(),
>   // accumulating the hash of the function "structure." (BB and opcode sequence)
>   BBs.push_back(&F.getEntryBlock());
>   VisitedBBs.insert(BBs[0]);
> @@ -1163,14 +1256,31 @@ class MergeFunctions : public ModulePass
> public:
>   static char ID;
>   MergeFunctions()
> -    : ModulePass(ID), HasGlobalAliases(false) {
> +    : ModulePass(ID), FnTree(FunctionNodeCmp(&GlobalNumbers)),
> +      HasGlobalAliases(false) {
>     initializeMergeFunctionsPass(*PassRegistry::getPassRegistry());
>   }
> 
>   bool runOnModule(Module &M) override;
> 
> private:
> -  typedef std::set<FunctionNode> FnTreeType;
> +  // The function comparison operator is provided here so that FunctionNodes do
> +  // not need to become larger with another pointer.
> +  class FunctionNodeCmp {
> +    GlobalNumberState* GlobalNumbers;
> +  public:
> +    FunctionNodeCmp(GlobalNumberState* GN) : GlobalNumbers(GN) {}
> +    bool operator()(const FunctionNode &LHS, const FunctionNode &RHS) const {
> +      // Order first by hashes, then full function comparison.
> +      if (LHS.getHash() != RHS.getHash())
> +        return LHS.getHash() < RHS.getHash();
> +      FunctionComparator FCmp(LHS.getFunc(), RHS.getFunc(), GlobalNumbers);
> +      return FCmp.compare() == -1;
> +    }
> +  };
> +  typedef std::set<FunctionNode, FunctionNodeCmp> FnTreeType;
> +
> +  GlobalNumberState GlobalNumbers;
> 
>   /// A work queue of functions that may have been modified and should be
>   /// analyzed again.
> @@ -1245,8 +1355,8 @@ bool MergeFunctions::doSanityCheck(std::
>       for (std::vector<WeakVH>::iterator J = I; J != E && j < Max; ++J, ++j) {
>         Function *F1 = cast<Function>(*I);
>         Function *F2 = cast<Function>(*J);
> -        int Res1 = FunctionComparator(F1, F2).compare();
> -        int Res2 = FunctionComparator(F2, F1).compare();
> +        int Res1 = FunctionComparator(F1, F2, &GlobalNumbers).compare();
> +        int Res2 = FunctionComparator(F2, F1, &GlobalNumbers).compare();
> 
>         // If F1 <= F2, then F2 >= F1, otherwise report failure.
>         if (Res1 != -Res2) {
> @@ -1267,8 +1377,8 @@ bool MergeFunctions::doSanityCheck(std::
>             continue;
> 
>           Function *F3 = cast<Function>(*K);
> -          int Res3 = FunctionComparator(F1, F3).compare();
> -          int Res4 = FunctionComparator(F2, F3).compare();
> +          int Res3 = FunctionComparator(F1, F3, &GlobalNumbers).compare();
> +          int Res4 = FunctionComparator(F2, F3, &GlobalNumbers).compare();
> 
>           bool Transitive = true;
> 
> @@ -1556,6 +1666,8 @@ void MergeFunctions::replaceFunctionInTr
>           (!F->mayBeOverridden() && !G->mayBeOverridden())) &&
>          "Only change functions if both are strong or both are weak");
>   (void)F;
> +  assert(FunctionComparator(F, G, &GlobalNumbers).compare() == 0 &&
> +         "The two functions must be equal");
> 
>   IterToF->replaceBy(G);
> }
> 
> Added: llvm/trunk/test/Transforms/MergeFunc/constant-entire-value.ll
> URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_Transforms_MergeFunc_constant-2Dentire-2Dvalue.ll-3Frev-3D245762-26view-3Dauto&d=BQIGaQ&c=eEvniauFctOgLOKGJOplqw&r=v-ruWq0KCv2O3thJZiK6naxuXK8mQHZUmGq5FBtAmZ4&m=8AXWbmpresvhRsDs49PoX5gvb_41wieiXuHyjTJ5YMo&s=XV-m4M5ffPZ4yM6fTcQlJGawM37EGxaZ-ixc9lXpz7w&e= 
> ==============================================================================
> --- llvm/trunk/test/Transforms/MergeFunc/constant-entire-value.ll (added)
> +++ llvm/trunk/test/Transforms/MergeFunc/constant-entire-value.ll Fri Aug 21 18:27:24 2015
> @@ -0,0 +1,42 @@
> +; RUN: opt -S -mergefunc < %s | FileCheck %s
> +
> +; RUN: opt -S -mergefunc < %s | FileCheck -check-prefix=NOPLUS %s
> +
> +; This makes sure that zeros in constants don't cause problems with string based
> +; memory comparisons
> +define internal i32 @sum(i32 %x, i32 %y) {
> +; CHECK-LABEL: @sum
> +  %sum = add i32 %x, %y
> +  %1 = extractvalue [3 x i32] [ i32 3, i32 0, i32 2 ], 2
> +  %sum2 = add i32 %sum, %1
> +  %sum3 = add i32 %sum2, %y
> +  ret i32 %sum3
> +}
> +
> +define internal i32 @add(i32 %x, i32 %y) {
> +; CHECK-LABEL: @add
> +  %sum = add i32 %x, %y
> +  %1 = extractvalue [3 x i32] [ i32 3, i32 0, i32 1 ], 2
> +  %sum2 = add i32 %sum, %1
> +  %sum3 = add i32 %sum2, %y
> +  ret i32 %sum3
> +}
> +
> +define internal i32 @plus(i32 %x, i32 %y) {
> +; NOPLUS-NOT: @plus
> +  %sum = add i32 %x, %y
> +  %1 = extractvalue [3 x i32] [ i32 3, i32 0, i32 5 ], 2
> +  %sum2 = add i32 %sum, %1
> +  %sum3 = add i32 %sum2, %y
> +  ret i32 %sum3
> +}
> +
> +define internal i32 @next(i32 %x, i32 %y) {
> +; CHECK-LABEL: @next
> +  %sum = add i32 %x, %y
> +  %1 = extractvalue [3 x i32] [ i32 3, i32 0, i32 5 ], 2
> +  %sum2 = add i32 %sum, %1
> +  %sum3 = add i32 %sum2, %y
> +  ret i32 %sum3
> +}
> +
> 
> 
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