SimplifyCFG: Refactor GatherConstantCompares() result in a struct

Code seems cleaner and easier to understand this way

llvm-svn: 222416

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -357,29 +357,55 @@ static ConstantInt *GetConstantInt(Value *V, const DataLayout *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
 
-// Try to match Instruction I as a comparison against a constant and populates
+  /// Construct and compute the result for the comparison instruction Cond
-// Vals with the set of value that match (or does not depending on isEQ).
+  ConstantComparesGatherer(Instruction *Cond, const DataLayout *DL) {
-// Return nullptr on failure, or return the Value the comparison matched against
+    gather(Cond, DL);
-// 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) {
 
+  /// 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 nullptr;
+      return false;
     }
 
     Value *RHSVal;
@@ -394,20 +420,20 @@ static Value* GatherConstantComparesMatch(Instruction *I,
         APInt Not = ~RHSC->getValue();
         if (Not.isPowerOf2()) {
           // If we already have a value for the switch, it has to match!
-        if(CurrValue && CurrValue != RHSVal)
+          if(!setValueOnce(RHSVal))
-          return nullptr;
+            return false;
 
           Vals.push_back(C);
           Vals.push_back(ConstantInt::get(C->getContext(),
                                           C->getValue() | Not));
           UsedICmps++;
-        return RHSVal;
+          return true;
         }
       }
 
       // If we already have a value for the switch, it has to match!
-    if(CurrValue && CurrValue != ICI->getOperand(0))
+      if(!setValueOnce(ICI->getOperand(0)))
-      return nullptr;
+        return false;
 
       UsedICmps++;
       Vals.push_back(C);
@@ -426,10 +452,6 @@ static Value* GatherConstantComparesMatch(Instruction *I,
       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.
@@ -438,29 +460,29 @@ static Value* GatherConstantComparesMatch(Instruction *I,
 
     // 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;
+      return false;
     }
 
+    // If we already have a value for the switch, it has to match!
+    if(!setValueOnce(CandidateVal))
+      return false;
+
     // 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;
+    return true;
 
-}
+  }
 
-/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
+  /// gather - Given a potentially 'or'd or 'and'd together collection of icmp
-/// collection of icmp eq/ne instructions that compare a value against a
+  /// eq/ne/lt/gt instructions that compare a value against a constant, extract
-/// constant, return the value being compared, and stick the constant into the
+  /// the value being compared, and stick the list constants into the Vals
-/// Values vector.
+  /// vector.
-/// One "Extra" case is allowed to differ from the other.
+  /// One "Extra" case is allowed to differ from the other.
-static Value *
+  void gather(Value *V, const DataLayout *DL) {
-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
@@ -469,14 +491,10 @@ GatherConstantCompares(Value *V, SmallVectorImpl<ConstantInt*> &Vals, Value *&Ex
     // 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)) {
-
         // 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));
@@ -485,32 +503,24 @@ GatherConstantCompares(Value *V, SmallVectorImpl<ConstantInt*> &Vals, Value *&Ex
         }
 
         // Try to match the current instruction
-      if (Value *Matched = GatherConstantComparesMatch(I,
+        if (matchInstruction(I, DL, isEQ))
-                                                       CurrValue,
-                                                       Vals,
-                                                       DL,
-                                                       UsedICmps,
-                                                       isEQ)) {
           // Match succeed, continue the loop
-        CurrValue = Matched;
           continue;
       }
-    }
 
       // 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) {
+      if (!Extra) {
         Extra = V;
         continue;
       }
-    return nullptr;
+      // Failed to parse a proper sequence, abort now
-
+      CompValue = nullptr;
+      break;
     }
-
+  }
-  // 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(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;
@@ -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);