[llvm] r222416 - SimplifyCFG: Refactor GatherConstantCompares() result in a struct
Mehdi Amini
mehdi.amini at apple.com
Wed Nov 19 22:51:03 PST 2014
Author: mehdi_amini
Date: Thu Nov 20 00:51:02 2014
New Revision: 222416
URL: http://llvm.org/viewvc/llvm-project?rev=222416&view=rev
Log:
SimplifyCFG: Refactor GatherConstantCompares() result in a struct
Code seems cleaner and easier to understand this way
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=222416&r1=222415&r2=222416&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Thu Nov 20 00:51:02 2014
@@ -357,160 +357,170 @@ static ConstantInt *GetConstantInt(Value
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);
+ }
+
+ /// Prevent copy
+ ConstantComparesGatherer(const ConstantComparesGatherer&) = delete;
+ ConstantComparesGatherer &operator=(const ConstantComparesGatherer&) = delete;
+
+private:
+
+ /// 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;
+ }
+
+ /// 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;
+ }
+ Value *RHSVal;
+ ConstantInt *RHSC;
-// 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;
- }
-
- 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;
+ // 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 we already have a value for the switch, it has to match!
- if(CurrValue && CurrValue != ICI->getOperand(0))
- return nullptr;
+ // If we already have a value for the switch, it has to match!
+ if(!setValueOnce(ICI->getOperand(0)))
+ return false;
- UsedICmps++;
- Vals.push_back(C);
- return ICI->getOperand(0);
- }
+ 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 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 have "x ult 3", for example, then we can add 0,1,2 to the set.
- ConstantRange Span = ConstantRange::makeICmpRegion(ICI->getPredicate(),
- C->getValue());
+ // 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;
+ }
- // 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(!setValueOnce(CandidateVal))
+ return false;
- // If we already have a value for the switch, it has to match!
- if(CurrValue && CurrValue != CandidateVal)
- 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));
- // 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();
+ UsedICmps++;
+ return true;
- // 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, 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);
-
- // Keep a stack (SmallVector for efficiency) for depth-first traversal
- SmallVector<Value *, 8> DFT;
-
- // Initialize
- DFT.push_back(V);
-
- // Will hold the value used for the switch comparison
- Value *CurrValue = nullptr;
-
- 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;
@@ -2810,18 +2820,17 @@ static bool SimplifyBranchOnICmpChain(Br
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;
@@ -2830,6 +2839,8 @@ static bool SimplifyBranchOnICmpChain(Br
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);
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