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-rw-r--r--llvm/lib/Transforms/Scalar/IndVarSimplify.cpp426
1 files changed, 200 insertions, 226 deletions
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index fabbf6e19e5..ccd25d8fb50 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -53,6 +53,7 @@
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
@@ -89,13 +90,14 @@ namespace {
void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
SmallPtrSet<Instruction*, 16> &DeadInsts);
- Instruction *LinearFunctionTestReplace(Loop *L, SCEV *IterationCount,
- SCEVExpander &RW);
+ void LinearFunctionTestReplace(Loop *L, SCEVHandle IterationCount, Value *IndVar,
+ BasicBlock *ExitingBlock,
+ BranchInst *BI,
+ SCEVExpander &Rewriter);
void RewriteLoopExitValues(Loop *L, SCEV *IterationCount);
void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts);
- void OptimizeCanonicalIVType(Loop *L);
void HandleFloatingPointIV(Loop *L, PHINode *PH,
SmallPtrSet<Instruction*, 16> &DeadInsts);
};
@@ -225,68 +227,54 @@ void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
/// variable. This pass is able to rewrite the exit tests of any loop where the
/// SCEV analysis can determine a loop-invariant trip count of the loop, which
/// is actually a much broader range than just linear tests.
-///
-/// This method returns a "potentially dead" instruction whose computation chain
-/// should be deleted when convenient.
-Instruction *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
- SCEV *IterationCount,
- SCEVExpander &RW) {
- // Find the exit block for the loop. We can currently only handle loops with
- // a single exit.
- SmallVector<BasicBlock*, 8> ExitBlocks;
- L->getExitBlocks(ExitBlocks);
- if (ExitBlocks.size() != 1) return 0;
- BasicBlock *ExitBlock = ExitBlocks[0];
-
- // Make sure there is only one predecessor block in the loop.
- BasicBlock *ExitingBlock = 0;
- for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
- PI != PE; ++PI)
- if (L->contains(*PI)) {
- if (ExitingBlock == 0)
- ExitingBlock = *PI;
- else
- return 0; // Multiple exits from loop to this block.
- }
- assert(ExitingBlock && "Loop info is broken");
-
- if (!isa<BranchInst>(ExitingBlock->getTerminator()))
- return 0; // Can't rewrite non-branch yet
- BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator());
- assert(BI->isConditional() && "Must be conditional to be part of loop!");
-
- Instruction *PotentiallyDeadInst = dyn_cast<Instruction>(BI->getCondition());
-
+void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
+ SCEVHandle IterationCount,
+ Value *IndVar,
+ BasicBlock *ExitingBlock,
+ BranchInst *BI,
+ SCEVExpander &Rewriter) {
// If the exiting block is not the same as the backedge block, we must compare
// against the preincremented value, otherwise we prefer to compare against
// the post-incremented value.
- BasicBlock *Header = L->getHeader();
- pred_iterator HPI = pred_begin(Header);
- assert(HPI != pred_end(Header) && "Loop with zero preds???");
- if (!L->contains(*HPI)) ++HPI;
- assert(HPI != pred_end(Header) && L->contains(*HPI) &&
- "No backedge in loop?");
-
- SCEVHandle TripCount = IterationCount;
- Value *IndVar;
- if (*HPI == ExitingBlock) {
+ Value *CmpIndVar;
+ if (ExitingBlock == L->getLoopLatch()) {
+ // What ScalarEvolution calls the "iteration count" is actually the
+ // number of times the branch is taken. Add one to get the number
+ // of times the branch is executed. If this addition may overflow,
+ // we have to be more pessimistic and cast the induction variable
+ // before doing the add.
+ SCEVHandle Zero = SE->getIntegerSCEV(0, IterationCount->getType());
+ SCEVHandle N =
+ SE->getAddExpr(IterationCount,
+ SE->getIntegerSCEV(1, IterationCount->getType()));
+ if ((isa<SCEVConstant>(N) && !N->isZero()) ||
+ SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
+ // No overflow. Cast the sum.
+ IterationCount = SE->getTruncateOrZeroExtend(N, IndVar->getType());
+ } else {
+ // Potential overflow. Cast before doing the add.
+ IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
+ IndVar->getType());
+ IterationCount =
+ SE->getAddExpr(IterationCount,
+ SE->getIntegerSCEV(1, IndVar->getType()));
+ }
+
// The IterationCount expression contains the number of times that the
// backedge actually branches to the loop header. This is one less than the
// number of times the loop executes, so add one to it.
- ConstantInt *OneC = ConstantInt::get(IterationCount->getType(), 1);
- TripCount = SE->getAddExpr(IterationCount, SE->getConstant(OneC));
- IndVar = L->getCanonicalInductionVariableIncrement();
+ CmpIndVar = L->getCanonicalInductionVariableIncrement();
} else {
// We have to use the preincremented value...
- IndVar = L->getCanonicalInductionVariable();
+ IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
+ IndVar->getType());
+ CmpIndVar = IndVar;
}
-
- DOUT << "INDVARS: LFTR: TripCount = " << *TripCount
- << " IndVar = " << *IndVar << "\n";
// Expand the code for the iteration count into the preheader of the loop.
BasicBlock *Preheader = L->getLoopPreheader();
- Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator());
+ Value *ExitCnt = Rewriter.expandCodeFor(IterationCount,
+ Preheader->getTerminator());
// Insert a new icmp_ne or icmp_eq instruction before the branch.
ICmpInst::Predicate Opcode;
@@ -295,14 +283,18 @@ Instruction *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
else
Opcode = ICmpInst::ICMP_EQ;
- Value *Cond = new ICmpInst(Opcode, IndVar, ExitCnt, "exitcond", BI);
+ DOUT << "INDVARS: Rewriting loop exit condition to:\n"
+ << " LHS:" << *CmpIndVar // includes a newline
+ << " op:\t"
+ << (Opcode == ICmpInst::ICMP_NE ? "!=" : "=") << "\n"
+ << " RHS:\t" << *IterationCount << "\n";
+
+ Value *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
BI->setCondition(Cond);
++NumLFTR;
Changed = true;
- return PotentiallyDeadInst;
}
-
/// RewriteLoopExitValues - Check to see if this loop has a computable
/// loop-invariant execution count. If so, this means that we can compute the
/// final value of any expressions that are recurrent in the loop, and
@@ -444,15 +436,100 @@ bool IndVarSimplify::doInitialization(Loop *L, LPPassManager &LPM) {
return Changed;
}
-bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
+/// getEffectiveIndvarType - Determine the widest type that the
+/// induction-variable PHINode Phi is cast to.
+///
+static const Type *getEffectiveIndvarType(const PHINode *Phi) {
+ const Type *Ty = Phi->getType();
+
+ for (Value::use_const_iterator UI = Phi->use_begin(), UE = Phi->use_end();
+ UI != UE; ++UI) {
+ const Type *CandidateType = NULL;
+ if (const ZExtInst *ZI = dyn_cast<ZExtInst>(UI))
+ CandidateType = ZI->getDestTy();
+ else if (const SExtInst *SI = dyn_cast<SExtInst>(UI))
+ CandidateType = SI->getDestTy();
+ if (CandidateType &&
+ CandidateType->getPrimitiveSizeInBits() >
+ Ty->getPrimitiveSizeInBits())
+ Ty = CandidateType;
+ }
+
+ return Ty;
+}
+
+/// isOrigIVAlwaysNonNegative - Analyze the original induction variable
+/// in the loop to determine whether it would ever have a negative
+/// value.
+///
+/// TODO: This duplicates a fair amount of ScalarEvolution logic.
+/// Perhaps this can be merged with ScalarEvolution::getIterationCount.
+///
+static bool isOrigIVAlwaysNonNegative(const Loop *L,
+ const Instruction *OrigCond) {
+ // Verify that the loop is sane and find the exit condition.
+ const ICmpInst *Cmp = dyn_cast<ICmpInst>(OrigCond);
+ if (!Cmp) return false;
+
+ // For now, analyze only SLT loops for signed overflow.
+ if (Cmp->getPredicate() != ICmpInst::ICMP_SLT) return false;
+
+ // Get the increment instruction. Look past SExtInsts if we will
+ // be able to prove that the original induction variable doesn't
+ // undergo signed overflow.
+ const Value *OrigIncrVal = Cmp->getOperand(0);
+ const Value *IncrVal = OrigIncrVal;
+ if (SExtInst *SI = dyn_cast<SExtInst>(Cmp->getOperand(0))) {
+ if (!isa<ConstantInt>(Cmp->getOperand(1)) ||
+ !cast<ConstantInt>(Cmp->getOperand(1))->getValue()
+ .isSignedIntN(IncrVal->getType()->getPrimitiveSizeInBits()))
+ return false;
+ IncrVal = SI->getOperand(0);
+ }
+ // For now, only analyze induction variables that have simple increments.
+ const BinaryOperator *IncrOp = dyn_cast<BinaryOperator>(IncrVal);
+ if (!IncrOp ||
+ IncrOp->getOpcode() != Instruction::Add ||
+ !isa<ConstantInt>(IncrOp->getOperand(1)) ||
+ !cast<ConstantInt>(IncrOp->getOperand(1))->equalsInt(1))
+ return false;
+
+ // Make sure the PHI looks like a normal IV.
+ const PHINode *PN = dyn_cast<PHINode>(IncrOp->getOperand(0));
+ if (!PN || PN->getNumIncomingValues() != 2)
+ return false;
+ unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
+ unsigned BackEdge = !IncomingEdge;
+ if (!L->contains(PN->getIncomingBlock(BackEdge)) ||
+ PN->getIncomingValue(BackEdge) != IncrOp)
+ return false;
+
+ // For now, only analyze loops with a constant start value, so that
+ // we can easily determine if the start value is non-negative and
+ // not a maximum value which would wrap on the first iteration.
+ const Value *InitialVal = PN->getIncomingValue(IncomingEdge);
+ if (!isa<ConstantInt>(InitialVal) ||
+ cast<ConstantInt>(InitialVal)->getValue().isNegative() ||
+ cast<ConstantInt>(InitialVal)->getValue().isMaxSignedValue())
+ return false;
+
+ // The original induction variable will start at some non-negative
+ // non-max value, it counts up by one, and the loop iterates only
+ // while it remans less than (signed) some value in the same type.
+ // As such, it will always be non-negative.
+ return true;
+}
+
+bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
Changed = false;
- BasicBlock *Header = L->getHeader();
+ BasicBlock *Header = L->getHeader();
+ BasicBlock *ExitingBlock = L->getExitingBlock();
SmallPtrSet<Instruction*, 16> DeadInsts;
-
+
// Verify the input to the pass in already in LCSSA form.
assert(L->isLCSSAForm());
@@ -486,35 +563,23 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
}
}
- // If there are no induction variables in the loop, there is nothing more to
- // do.
- if (IndVars.empty()) {
- // Actually, if we know how many times the loop iterates, lets insert a
- // canonical induction variable to help subsequent passes.
- if (!isa<SCEVCouldNotCompute>(IterationCount)) {
- SCEVExpander Rewriter(*SE, *LI);
- Rewriter.getOrInsertCanonicalInductionVariable(L,
- IterationCount->getType());
- if (Instruction *I = LinearFunctionTestReplace(L, IterationCount,
- Rewriter)) {
- SmallPtrSet<Instruction*, 16> InstructionsToDelete;
- InstructionsToDelete.insert(I);
- DeleteTriviallyDeadInstructions(InstructionsToDelete);
- }
- }
- return Changed;
+ // Compute the type of the largest recurrence expression, and collect
+ // the set of the types of the other recurrence expressions.
+ const Type *LargestType = 0;
+ SmallSetVector<const Type *, 4> SizesToInsert;
+ if (!isa<SCEVCouldNotCompute>(IterationCount)) {
+ LargestType = IterationCount->getType();
+ SizesToInsert.insert(IterationCount->getType());
}
-
- // Compute the type of the largest recurrence expression.
- //
- const Type *LargestType = IndVars[0].first->getType();
- bool DifferingSizes = false;
- for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
- const Type *Ty = IndVars[i].first->getType();
- DifferingSizes |=
- Ty->getPrimitiveSizeInBits() != LargestType->getPrimitiveSizeInBits();
- if (Ty->getPrimitiveSizeInBits() > LargestType->getPrimitiveSizeInBits())
- LargestType = Ty;
+ for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
+ const PHINode *PN = IndVars[i].first;
+ SizesToInsert.insert(PN->getType());
+ const Type *EffTy = getEffectiveIndvarType(PN);
+ SizesToInsert.insert(EffTy);
+ if (!LargestType ||
+ EffTy->getPrimitiveSizeInBits() >
+ LargestType->getPrimitiveSizeInBits())
+ LargestType = EffTy;
}
// Create a rewriter object which we'll use to transform the code with.
@@ -522,17 +587,32 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// Now that we know the largest of of the induction variables in this loop,
// insert a canonical induction variable of the largest size.
- Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
- ++NumInserted;
- Changed = true;
- DOUT << "INDVARS: New CanIV: " << *IndVar;
-
- if (!isa<SCEVCouldNotCompute>(IterationCount)) {
- IterationCount = SE->getTruncateOrZeroExtend(IterationCount, LargestType);
- if (Instruction *DI = LinearFunctionTestReplace(L, IterationCount,Rewriter))
- DeadInsts.insert(DI);
+ Value *IndVar = 0;
+ if (!SizesToInsert.empty()) {
+ IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
+ ++NumInserted;
+ Changed = true;
+ DOUT << "INDVARS: New CanIV: " << *IndVar;
}
+ // If we have a trip count expression, rewrite the loop's exit condition
+ // using it. We can currently only handle loops with a single exit.
+ bool OrigIVAlwaysNonNegative = false;
+ if (!isa<SCEVCouldNotCompute>(IterationCount) && ExitingBlock)
+ // Can't rewrite non-branch yet.
+ if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
+ if (Instruction *OrigCond = dyn_cast<Instruction>(BI->getCondition())) {
+ // Determine if the OrigIV will ever have a non-zero sign bit.
+ OrigIVAlwaysNonNegative = isOrigIVAlwaysNonNegative(L, OrigCond);
+
+ // We'll be replacing the original condition, so it'll be dead.
+ DeadInsts.insert(OrigCond);
+ }
+
+ LinearFunctionTestReplace(L, IterationCount, IndVar,
+ ExitingBlock, BI, Rewriter);
+ }
+
// Now that we have a canonical induction variable, we can rewrite any
// recurrences in terms of the induction variable. Start with the auxillary
// induction variables, and recursively rewrite any of their uses.
@@ -541,21 +621,13 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// If there were induction variables of other sizes, cast the primary
// induction variable to the right size for them, avoiding the need for the
// code evaluation methods to insert induction variables of different sizes.
- if (DifferingSizes) {
- SmallVector<unsigned,4> InsertedSizes;
- InsertedSizes.push_back(LargestType->getPrimitiveSizeInBits());
- for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
- unsigned ithSize = IndVars[i].first->getType()->getPrimitiveSizeInBits();
- if (std::find(InsertedSizes.begin(), InsertedSizes.end(), ithSize)
- == InsertedSizes.end()) {
- PHINode *PN = IndVars[i].first;
- InsertedSizes.push_back(ithSize);
- Instruction *New = new TruncInst(IndVar, PN->getType(), "indvar",
- InsertPt);
- Rewriter.addInsertedValue(New, SE->getSCEV(New));
- DOUT << "INDVARS: Made trunc IV for " << *PN
- << " NewVal = " << *New << "\n";
- }
+ for (unsigned i = 0, e = SizesToInsert.size(); i != e; ++i) {
+ const Type *Ty = SizesToInsert[i];
+ if (Ty != LargestType) {
+ Instruction *New = new TruncInst(IndVar, Ty, "indvar", InsertPt);
+ Rewriter.addInsertedValue(New, SE->getSCEV(New));
+ DOUT << "INDVARS: Made trunc IV for type " << *Ty << ": "
+ << *New << "\n";
}
}
@@ -568,6 +640,23 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
<< " into = " << *NewVal << "\n";
NewVal->takeName(PN);
+ /// If the new canonical induction variable is wider than the original,
+ /// and the original has uses that are casts to wider types, see if the
+ /// truncate and extend can be omitted.
+ if (isa<TruncInst>(NewVal))
+ for (Value::use_iterator UI = PN->use_begin(), UE = PN->use_end();
+ UI != UE; ++UI)
+ if (isa<ZExtInst>(UI) ||
+ (isa<SExtInst>(UI) && OrigIVAlwaysNonNegative)) {
+ Value *TruncIndVar = IndVar;
+ if (TruncIndVar->getType() != UI->getType())
+ TruncIndVar = new TruncInst(IndVar, UI->getType(), "truncindvar",
+ InsertPt);
+ UI->replaceAllUsesWith(TruncIndVar);
+ if (Instruction *DeadUse = dyn_cast<Instruction>(*UI))
+ DeadInsts.insert(DeadUse);
+ }
+
// Replace the old PHI Node with the inserted computation.
PN->replaceAllUsesWith(NewVal);
DeadInsts.insert(PN);
@@ -603,125 +692,10 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
#endif
DeleteTriviallyDeadInstructions(DeadInsts);
- OptimizeCanonicalIVType(L);
assert(L->isLCSSAForm());
return Changed;
}
-/// OptimizeCanonicalIVType - If loop induction variable is always
-/// sign or zero extended then extend the type of the induction
-/// variable.
-void IndVarSimplify::OptimizeCanonicalIVType(Loop *L) {
- PHINode *PH = L->getCanonicalInductionVariable();
- if (!PH) return;
-
- // Check loop iteration count.
- SCEVHandle IC = SE->getIterationCount(L);
- if (isa<SCEVCouldNotCompute>(IC)) return;
- SCEVConstant *IterationCount = dyn_cast<SCEVConstant>(IC);
- if (!IterationCount) return;
-
- unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
- unsigned BackEdge = IncomingEdge^1;
-
- // Check IV uses. If all IV uses are either SEXT or ZEXT (except
- // IV increment instruction) then this IV is suitable for this
- // transformation.
- bool isSEXT = false;
- BinaryOperator *Incr = NULL;
- const Type *NewType = NULL;
- for(Value::use_iterator UI = PH->use_begin(), UE = PH->use_end();
- UI != UE; ++UI) {
- const Type *CandidateType = NULL;
- if (ZExtInst *ZI = dyn_cast<ZExtInst>(UI))
- CandidateType = ZI->getDestTy();
- else if (SExtInst *SI = dyn_cast<SExtInst>(UI)) {
- CandidateType = SI->getDestTy();
- isSEXT = true;
- }
- else if ((Incr = dyn_cast<BinaryOperator>(UI))) {
- // Validate IV increment instruction.
- if (PH->getIncomingValue(BackEdge) == Incr)
- continue;
- }
- if (!CandidateType) {
- NewType = NULL;
- break;
- }
- if (!NewType)
- NewType = CandidateType;
- else if (NewType != CandidateType) {
- NewType = NULL;
- break;
- }
- }
-
- // IV uses are not suitable then avoid this transformation.
- if (!NewType || !Incr)
- return;
-
- // IV increment instruction has two uses, one is loop exit condition
- // and second is the IV (phi node) itself.
- ICmpInst *Exit = NULL;
- for(Value::use_iterator II = Incr->use_begin(), IE = Incr->use_end();
- II != IE; ++II) {
- if (PH == *II) continue;
- Exit = dyn_cast<ICmpInst>(*II);
- break;
- }
- if (!Exit) return;
- ConstantInt *EV = dyn_cast<ConstantInt>(Exit->getOperand(0));
- if (!EV)
- EV = dyn_cast<ConstantInt>(Exit->getOperand(1));
- if (!EV) return;
-
- // Check iteration count max value to avoid loops that wrap around IV.
- APInt ICount = IterationCount->getValue()->getValue();
- if (ICount.isNegative()) return;
- uint32_t BW = PH->getType()->getPrimitiveSizeInBits();
- APInt Max = (isSEXT ? APInt::getSignedMaxValue(BW) : APInt::getMaxValue(BW));
- if (ICount.getZExtValue() > Max.getZExtValue()) return;
-
- // Extend IV type.
-
- SCEVExpander Rewriter(*SE, *LI);
- Value *NewIV = Rewriter.getOrInsertCanonicalInductionVariable(L,NewType);
- PHINode *NewPH = cast<PHINode>(NewIV);
- Instruction *NewIncr = cast<Instruction>(NewPH->getIncomingValue(BackEdge));
-
- // Replace all SEXT or ZEXT uses.
- SmallVector<Instruction *, 4> PHUses;
- for(Value::use_iterator UI = PH->use_begin(), UE = PH->use_end();
- UI != UE; ++UI) {
- Instruction *I = cast<Instruction>(UI);
- PHUses.push_back(I);
- }
- while (!PHUses.empty()){
- Instruction *Use = PHUses.back(); PHUses.pop_back();
- if (Incr == Use) continue;
-
- SE->deleteValueFromRecords(Use);
- Use->replaceAllUsesWith(NewIV);
- Use->eraseFromParent();
- }
-
- // Replace exit condition.
- ConstantInt *NEV = ConstantInt::get(NewType, EV->getZExtValue());
- Instruction *NE = new ICmpInst(Exit->getPredicate(),
- NewIncr, NEV, "new.exit",
- Exit->getParent()->getTerminator());
- SE->deleteValueFromRecords(Exit);
- Exit->replaceAllUsesWith(NE);
- Exit->eraseFromParent();
-
- // Remove old IV and increment instructions.
- SE->deleteValueFromRecords(PH);
- PH->removeIncomingValue((unsigned)0);
- PH->removeIncomingValue((unsigned)0);
- SE->deleteValueFromRecords(Incr);
- Incr->eraseFromParent();
-}
-
/// Return true if it is OK to use SIToFPInst for an inducation variable
/// with given inital and exit values.
static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
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