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SimplifyCFG: turn recursive GatherConstantCompares into iterative

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A long sequence of || or && could lead to a stack explosion.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222384 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Mehdi Amini 2014-11-19 20:09:11 +00:00
parent 6e0f244d1f
commit 30bd0c753e
1 changed files with 139 additions and 100 deletions

239
lib/Transforms/Utils/SimplifyCFG.cpp

@ -357,114 +357,159 @@ 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 (not ((ICI = dyn_cast<ICmpInst>(I)) &&
(C = GetConstantInt(I->getOperand(1), DL)))) {
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(CurrValue && CurrValue != RHSVal)
return nullptr;
Vals.push_back(C);
Vals.push_back(ConstantInt::get(C->getContext(),
C->getValue() | Not));
UsedICmps++;
return RHSVal;
}
}
// If we already have a value for the switch, it has to match!
if(CurrValue && CurrValue != ICI->getOperand(0))
return nullptr;
UsedICmps++;
Vals.push_back(C);
return ICI->getOperand(0);
}
// 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;
}
// If we already have a value for the switch, it has to match!
if(CurrValue && CurrValue != CandidateVal)
return nullptr;
// 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 there are a ton of values, we don't want to make a ginormous switch.
if (Span.getSetSize().ugt(8) || Span.isEmptySet()) {
return nullptr;
}
// 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));
UsedICmps++;
return CandidateVal;
}
/// 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, std::vector<ConstantInt*> &Vals, Value *&Extra,
const DataLayout *DL, bool isEQ, unsigned &UsedICmps) {
GatherConstantCompares(Value *V, SmallVectorImpl<ConstantInt*> &Vals, Value *&Extra,
const DataLayout *DL, unsigned &UsedICmps) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return nullptr;
// If this is an icmp against a constant, handle this as one of the cases.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
if (ConstantInt *C = GetConstantInt(I->getOperand(1), DL)) {
Value *RHSVal;
ConstantInt *RHSC;
bool isEQ = (I->getOpcode() == Instruction::Or);
if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
// (x & ~2^x) == y --> x == y || x == y|2^x
// This undoes a transformation done by instcombine to fuse 2 compares.
if (match(ICI->getOperand(0),
m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
APInt Not = ~RHSC->getValue();
if (Not.isPowerOf2()) {
Vals.push_back(C);
Vals.push_back(
ConstantInt::get(C->getContext(), C->getValue() | Not));
UsedICmps++;
return RHSVal;
}
}
// Keep a stack (SmallVector for efficiency) for depth-first traversal
SmallVector<Value *, 8> DFT;
UsedICmps++;
Vals.push_back(C);
return I->getOperand(0);
// Initialize
DFT.push_back(V);
// Will hold the value used for the switch comparison
Value *CurrValue = nullptr;
while(not 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 we have "x ult 3" comparison, 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.
bool hasAdd =
match(I->getOperand(0), m_Add(m_Value(RHSVal), m_ConstantInt(RHSC)));
if (hasAdd)
Span = Span.subtract(RHSC->getValue());
// If this is an and/!= check then we want to optimize "x ugt 2" into
// x != 0 && x != 1.
if (!isEQ)
Span = Span.inverse();
// 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;
for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
UsedICmps++;
return hasAdd ? RHSVal : I->getOperand(0);
}
return nullptr;
}
// Otherwise, we can only handle an | or &, depending on isEQ.
if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
return nullptr;
unsigned NumValsBeforeLHS = Vals.size();
unsigned UsedICmpsBeforeLHS = UsedICmps;
if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, DL,
isEQ, UsedICmps)) {
unsigned NumVals = Vals.size();
unsigned UsedICmpsBeforeRHS = UsedICmps;
if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, DL,
isEQ, UsedICmps)) {
if (LHS == RHS)
return LHS;
Vals.resize(NumVals);
UsedICmps = UsedICmpsBeforeRHS;
// Try to match the current instruction
if (Value *Matched = GatherConstantComparesMatch(I,
CurrValue,
Vals,
DL,
UsedICmps,
isEQ)) {
// Match succeed, continue the loop
CurrValue = Matched;
continue;
}
}
// The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
// set it and return success.
if (Extra == nullptr || Extra == I->getOperand(1)) {
Extra = I->getOperand(1);
return LHS;
// 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;
}
Vals.resize(NumValsBeforeLHS);
UsedICmps = UsedICmpsBeforeLHS;
return nullptr;
}
// If the LHS can't be folded in, but Extra is available and RHS can, try to
// use LHS as Extra.
if (Extra == nullptr || Extra == I->getOperand(0)) {
Value *OldExtra = Extra;
Extra = I->getOperand(0);
if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, DL,
isEQ, UsedICmps))
return RHS;
assert(Vals.size() == NumValsBeforeLHS);
Extra = OldExtra;
}
return nullptr;
// Return the value to be used for the switch comparison (if any)
return CurrValue;
}
static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
@ -2770,19 +2815,13 @@ static bool SimplifyBranchOnICmpChain(BranchInst *BI, const DataLayout *DL,
// 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;
std::vector<ConstantInt*> Values;
bool TrueWhenEqual = true;
SmallVector<ConstantInt*, 8> Values;
bool TrueWhenEqual = (Cond->getOpcode() == Instruction::Or);
Value *ExtraCase = nullptr;
unsigned UsedICmps = 0;
if (Cond->getOpcode() == Instruction::Or) {
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, DL, true,
UsedICmps);
} else if (Cond->getOpcode() == Instruction::And) {
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, DL, false,
UsedICmps);
TrueWhenEqual = false;
}
// Try to gather values from a chain of and/or to be turned into a switch
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, DL, UsedICmps);
// If we didn't have a multiply compared value, fail.
if (!CompVal) return false;