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SimplifyCFG: Refactor GatherConstantCompares() result in a struct
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Code seems cleaner and easier to understand this way




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222416 91177308-0d34-0410-b5e6-96231b3b80d8
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@joker-eph
joker-eph committed Nov 20, 2014
1 parent dc0b300 commit b3e705e
Showing 1 changed file with 147 additions and 136 deletions.
283 changes: 147 additions & 136 deletions lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -357,160 +357,170 @@ static ConstantInt *GetConstantInt(Value *V, const DataLayout *DL) {
return nullptr;
}



// Try to match Instruction I as a comparison against a constant and populates
// Vals with the set of value that match (or does not depending on isEQ).
// Return nullptr on failure, or return the Value the comparison matched against
// on success
// CurrValue, if supplied, is the value we want to match against. The function
// is expected to fail if a match is found but the value compared to is not the
// one expected. If CurrValue is supplied, the return value has to be either
// nullptr or CurrValue
static Value* GatherConstantComparesMatch(Instruction *I,
Value *CurrValue,
SmallVectorImpl<ConstantInt*> &Vals,
const DataLayout *DL,
unsigned &UsedICmps,
bool isEQ) {

// If this is an icmp against a constant, handle this as one of the cases.
ICmpInst *ICI;
ConstantInt *C;
if (!((ICI = dyn_cast<ICmpInst>(I)) &&
(C = GetConstantInt(I->getOperand(1), DL)))) {
return nullptr;
/// Given a chain of or (||) or and (&&) comparison of a value against a
/// constant, this will try to recover the information required for a switch
/// structure.
/// It will depth-first traverse the chain of comparison, seeking for patterns
/// like %a == 12 or %a < 4 and combine them to produce a set of integer
/// representing the different cases for the switch.
/// Note that if the chain is composed of '||' it will build the set of elements
/// that matches the comparisons (i.e. any of this value validate the chain)
/// while for a chain of '&&' it will build the set elements that make the test
/// fail.
struct ConstantComparesGatherer {

Value *CompValue = nullptr; /// Value found for the switch comparison
Value *Extra = nullptr; /// Extra clause to be checked before the switch
SmallVector<ConstantInt*, 8> Vals; /// Set of integers to match in switch
unsigned UsedICmps = 0; /// Number of comparisons matched in the and/or chain

/// Construct and compute the result for the comparison instruction Cond
ConstantComparesGatherer(Instruction *Cond, const DataLayout *DL) {
gather(Cond, DL);
}

Value *RHSVal;
ConstantInt *RHSC;

// Pattern match a special case
// (x & ~2^x) == y --> x == y || x == y|2^x
// This undoes a transformation done by instcombine to fuse 2 compares.
if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
if (match(ICI->getOperand(0),
m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
APInt Not = ~RHSC->getValue();
if (Not.isPowerOf2()) {
// If we already have a value for the switch, it has to match!
if(CurrValue && CurrValue != RHSVal)
return nullptr;

Vals.push_back(C);
Vals.push_back(ConstantInt::get(C->getContext(),
C->getValue() | Not));
UsedICmps++;
return RHSVal;
}
}
/// Prevent copy
ConstantComparesGatherer(const ConstantComparesGatherer&) = delete;
ConstantComparesGatherer &operator=(const ConstantComparesGatherer&) = delete;

// If we already have a value for the switch, it has to match!
if(CurrValue && CurrValue != ICI->getOperand(0))
return nullptr;
private:

UsedICmps++;
Vals.push_back(C);
return ICI->getOperand(0);
/// Try to set the current value used for the comparison, it succeeds only if
/// it wasn't set before or if the new value is the same as the old one
bool setValueOnce(Value *NewVal) {
if(CompValue && CompValue != NewVal) return false;
return CompValue = NewVal;
}

// If we have "x ult 3", for example, then we can add 0,1,2 to the set.
ConstantRange Span = ConstantRange::makeICmpRegion(ICI->getPredicate(),
C->getValue());

// Shift the range if the compare is fed by an add. This is the range
// compare idiom as emitted by instcombine.
Value *CandidateVal = I->getOperand(0);
if(match(I->getOperand(0), m_Add(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
Span = Span.subtract(RHSC->getValue());
CandidateVal = RHSVal;
}
/// Try to match Instruction "I" as a comparison against a constant and
/// populates the array Vals with the set of values that match (or do not
/// match depending on isEQ).
/// Return false on failure. On success, the Value the comparison matched
/// against is placed in CompValue.
/// If CompValue is already set, the function is expected to fail if a match
/// is found but the value compared to is different.
bool matchInstruction(Instruction *I, const DataLayout *DL, bool isEQ) {
// If this is an icmp against a constant, handle this as one of the cases.
ICmpInst *ICI;
ConstantInt *C;
if (!((ICI = dyn_cast<ICmpInst>(I)) &&
(C = GetConstantInt(I->getOperand(1), DL)))) {
return false;
}

// If we already have a value for the switch, it has to match!
if(CurrValue && CurrValue != CandidateVal)
return nullptr;
Value *RHSVal;
ConstantInt *RHSC;

// Pattern match a special case
// (x & ~2^x) == y --> x == y || x == y|2^x
// This undoes a transformation done by instcombine to fuse 2 compares.
if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
if (match(ICI->getOperand(0),
m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
APInt Not = ~RHSC->getValue();
if (Not.isPowerOf2()) {
// If we already have a value for the switch, it has to match!
if(!setValueOnce(RHSVal))
return false;

Vals.push_back(C);
Vals.push_back(ConstantInt::get(C->getContext(),
C->getValue() | Not));
UsedICmps++;
return true;
}
}

// If this is an and/!= check, then we are looking to build the set of
// value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
// x != 0 && x != 1.
if (!isEQ)
Span = Span.inverse();
// If we already have a value for the switch, it has to match!
if(!setValueOnce(ICI->getOperand(0)))
return false;

// If there are a ton of values, we don't want to make a ginormous switch.
if (Span.getSetSize().ugt(8) || Span.isEmptySet()) {
return nullptr;
}
UsedICmps++;
Vals.push_back(C);
return ICI->getOperand(0);
}

// Add all values from the range to the set
for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
Vals.push_back(ConstantInt::get(I->getContext(), Tmp));
// If we have "x ult 3", for example, then we can add 0,1,2 to the set.
ConstantRange Span = ConstantRange::makeICmpRegion(ICI->getPredicate(),
C->getValue());

UsedICmps++;
return CandidateVal;
// Shift the range if the compare is fed by an add. This is the range
// compare idiom as emitted by instcombine.
Value *CandidateVal = I->getOperand(0);
if(match(I->getOperand(0), m_Add(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
Span = Span.subtract(RHSC->getValue());
CandidateVal = RHSVal;
}

}
// If this is an and/!= check, then we are looking to build the set of
// value that *don't* pass the and chain. I.e. to turn "x ugt 2" into
// x != 0 && x != 1.
if (!isEQ)
Span = Span.inverse();

/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
/// collection of icmp eq/ne instructions that compare a value against a
/// constant, return the value being compared, and stick the constant into the
/// Values vector.
/// One "Extra" case is allowed to differ from the other.
static Value *
GatherConstantCompares(Value *V, SmallVectorImpl<ConstantInt*> &Vals, Value *&Extra,
const DataLayout *DL, unsigned &UsedICmps) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return nullptr;

bool isEQ = (I->getOpcode() == Instruction::Or);
// If there are a ton of values, we don't want to make a ginormous switch.
if (Span.getSetSize().ugt(8) || Span.isEmptySet()) {
return false;
}

// Keep a stack (SmallVector for efficiency) for depth-first traversal
SmallVector<Value *, 8> DFT;
// If we already have a value for the switch, it has to match!
if(!setValueOnce(CandidateVal))
return false;

// Initialize
DFT.push_back(V);
// Add all values from the range to the set
for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
Vals.push_back(ConstantInt::get(I->getContext(), Tmp));

// Will hold the value used for the switch comparison
Value *CurrValue = nullptr;
UsedICmps++;
return true;

while(!DFT.empty()) {
V = DFT.pop_back_val();
}

if (Instruction *I = dyn_cast<Instruction>(V)) {
/// gather - Given a potentially 'or'd or 'and'd together collection of icmp
/// eq/ne/lt/gt instructions that compare a value against a constant, extract
/// the value being compared, and stick the list constants into the Vals
/// vector.
/// One "Extra" case is allowed to differ from the other.
void gather(Value *V, const DataLayout *DL) {
Instruction *I = dyn_cast<Instruction>(V);
bool isEQ = (I->getOpcode() == Instruction::Or);

// Keep a stack (SmallVector for efficiency) for depth-first traversal
SmallVector<Value *, 8> DFT;

// Initialize
DFT.push_back(V);

while(!DFT.empty()) {
V = DFT.pop_back_val();

if (Instruction *I = dyn_cast<Instruction>(V)) {
// If it is a || (or && depending on isEQ), process the operands.
if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
DFT.push_back(I->getOperand(1));
DFT.push_back(I->getOperand(0));
continue;
}

// If it is a || (or && depending on isEQ), process the operands.
if (I->getOpcode() == (isEQ ? Instruction::Or : Instruction::And)) {
DFT.push_back(I->getOperand(1));
DFT.push_back(I->getOperand(0));
continue;
// Try to match the current instruction
if (matchInstruction(I, DL, isEQ))
// Match succeed, continue the loop
continue;
}

// Try to match the current instruction
if (Value *Matched = GatherConstantComparesMatch(I,
CurrValue,
Vals,
DL,
UsedICmps,
isEQ)) {
// Match succeed, continue the loop
CurrValue = Matched;
// One element of the sequence of || (or &&) could not be match as a
// comparison against the same value as the others.
// We allow only one "Extra" case to be checked before the switch
if (!Extra) {
Extra = V;
continue;
}
// Failed to parse a proper sequence, abort now
CompValue = nullptr;
break;
}

// One element of the sequence of || (or &&) could not be match as a
// comparison against the same value as the others.
// We allow only one "Extra" case to be checked before the switch
if (Extra == nullptr) {
Extra = V;
continue;
}
return nullptr;

}

// Return the value to be used for the switch comparison (if any)
return CurrValue;
}
};

static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
Instruction *Cond = nullptr;
Expand Down Expand Up @@ -2810,18 +2820,17 @@ static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *DL,
Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
if (!Cond) return false;


// Change br (X == 0 | X == 1), T, F into a switch instruction.
// If this is a bunch of seteq's or'd together, or if it's a bunch of
// 'setne's and'ed together, collect them.
Value *CompVal = nullptr;
SmallVector<ConstantInt*, 8> Values;
bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
Value *ExtraCase = nullptr;
unsigned UsedICmps = 0;

// Try to gather values from a chain of and/or to be turned into a switch
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, DL, UsedICmps);
ConstantComparesGatherer ConstantCompare{Cond, DL};
// Unpack the result
SmallVectorImpl<ConstantInt*> &Values = ConstantCompare.Vals;
Value *CompVal = ConstantCompare.CompValue;
unsigned UsedICmps = ConstantCompare.UsedICmps;
Value *ExtraCase = ConstantCompare.Extra;

// If we didn't have a multiply compared value, fail.
if (!CompVal) return false;
Expand All @@ -2830,6 +2839,8 @@ static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *DL,
if (UsedICmps <= 1)
return false;

bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);

// There might be duplicate constants in the list, which the switch
// instruction can't handle, remove them now.
array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
Expand Down

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