Add 'umax' similar to 'smax' SCEV. Closes PR2003.

Parse reversed smax and umax as smin and umin and express them with negative
or binary-not SCEVs (which are really just subtract under the hood).

Parse 'xor %x, -1' as (-1 - %x).

Remove dead code (ConstantInt::get always returns a ConstantInt).

Don't use getIntegerSCEV(-1, Ty). The first value is an int, then it gets
passed into a uint64_t. Instead, create the -1 directly from
ConstantInt::getAllOnesValue().

llvm-svn: 47360

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -237,12 +237,18 @@ namespace llvm {
     }
     SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
     SCEVHandle getSMaxExpr(std::vector<SCEVHandle> Operands);
+    SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
+    SCEVHandle getUMaxExpr(std::vector<SCEVHandle> Operands);
     SCEVHandle getUnknown(Value *V);
 
     /// getNegativeSCEV - Return the SCEV object corresponding to -V.
     ///
     SCEVHandle getNegativeSCEV(const SCEVHandle &V);
 
+    /// getNotSCEV - Return the SCEV object corresponding to ~V.
+    ///
+    SCEVHandle getNotSCEV(const SCEVHandle &V);
+
     /// getMinusSCEV - Return LHS-RHS.
     ///
     SCEVHandle getMinusSCEV(const SCEVHandle &LHS,

llvm/include/llvm/Analysis/ScalarEvolutionExpander.h

@@ -136,6 +136,8 @@ namespace llvm {
 
     Value *visitSMaxExpr(SCEVSMaxExpr *S);
 
+    Value *visitUMaxExpr(SCEVUMaxExpr *S);
+
     Value *visitUnknown(SCEVUnknown *S) {
       return S->getValue();
     }

llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h

@@ -25,7 +25,8 @@ namespace llvm {
     // These should be ordered in terms of increasing complexity to make the
     // folders simpler.
     scConstant, scTruncate, scZeroExtend, scSignExtend, scAddExpr, scMulExpr,
-    scUDivExpr, scAddRecExpr, scSMaxExpr, scUnknown, scCouldNotCompute
+    scUDivExpr, scAddRecExpr, scUMaxExpr, scSMaxExpr, scUnknown,
+    scCouldNotCompute
   };
 
   //===--------------------------------------------------------------------===//
@@ -275,7 +276,8 @@ namespace llvm {
     static inline bool classof(const SCEV *S) {
       return S->getSCEVType() == scAddExpr ||
              S->getSCEVType() == scMulExpr ||
-             S->getSCEVType() == scSMaxExpr;
+             S->getSCEVType() == scSMaxExpr ||
+             S->getSCEVType() == scUMaxExpr;
     }
   };
 
@@ -482,6 +484,27 @@ namespace llvm {
   };
 
 
+  //===--------------------------------------------------------------------===//
+  /// SCEVUMaxExpr - This class represents an unsigned maximum selection.
+  ///
+  class SCEVUMaxExpr : public SCEVCommutativeExpr {
+    friend class ScalarEvolution;
+
+    explicit SCEVUMaxExpr(const std::vector<SCEVHandle> &ops)
+      : SCEVCommutativeExpr(scUMaxExpr, ops) {
+    }
+
+  public:
+    virtual const char *getOperationStr() const { return " umax "; }
+
+    /// Methods for support type inquiry through isa, cast, and dyn_cast:
+    static inline bool classof(const SCEVUMaxExpr *S) { return true; }
+    static inline bool classof(const SCEV *S) {
+      return S->getSCEVType() == scUMaxExpr;
+    }
+  };
+
+
   //===--------------------------------------------------------------------===//
   /// SCEVUnknown - This means that we are dealing with an entirely unknown SCEV
   /// value, and only represent it as it's LLVM Value.  This is the "bottom"
@@ -546,6 +569,8 @@ namespace llvm {
         return ((SC*)this)->visitAddRecExpr((SCEVAddRecExpr*)S);
       case scSMaxExpr:
         return ((SC*)this)->visitSMaxExpr((SCEVSMaxExpr*)S);
+      case scUMaxExpr:
+        return ((SC*)this)->visitUMaxExpr((SCEVUMaxExpr*)S);
       case scUnknown:
         return ((SC*)this)->visitUnknown((SCEVUnknown*)S);
       case scCouldNotCompute:
@@ -565,4 +590,3 @@ namespace llvm {
 }
 
 #endif
-

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -320,6 +320,8 @@ replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
         return SE.getMulExpr(NewOps);
       else if (isa<SCEVSMaxExpr>(this))
         return SE.getSMaxExpr(NewOps);
+      else if (isa<SCEVUMaxExpr>(this))
+        return SE.getUMaxExpr(NewOps);
       else
         assert(0 && "Unknown commutative expr!");
     }
@@ -520,7 +522,16 @@ SCEVHandle ScalarEvolution::getNegativeSCEV(const SCEVHandle &V) {
   if (SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
     return getUnknown(ConstantExpr::getNeg(VC->getValue()));
 
-  return getMulExpr(V, getIntegerSCEV(-1, V->getType()));
+  return getMulExpr(V, getUnknown(ConstantInt::getAllOnesValue(V->getType())));
+}
+
+/// getNotSCEV - Return a SCEV corresponding to ~V = -1-V
+SCEVHandle ScalarEvolution::getNotSCEV(const SCEVHandle &V) {
+  if (SCEVConstant *VC = dyn_cast<SCEVConstant>(V))
+    return getUnknown(ConstantExpr::getNot(VC->getValue()));
+
+  SCEVHandle AllOnes = getUnknown(ConstantInt::getAllOnesValue(V->getType()));
+  return getMinusSCEV(AllOnes, V);
 }
 
 /// getMinusSCEV - Return a SCEV corresponding to LHS - RHS.
@@ -709,19 +720,12 @@ SCEVHandle ScalarEvolution::getAddExpr(std::vector<SCEVHandle> &Ops) {
     assert(Idx < Ops.size());
     while (SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {
       // We found two constants, fold them together!
-      Constant *Fold = ConstantInt::get(LHSC->getValue()->getValue() + 
+      ConstantInt *Fold = ConstantInt::get(LHSC->getValue()->getValue() + 
                                            RHSC->getValue()->getValue());
-      if (ConstantInt *CI = dyn_cast<ConstantInt>(Fold)) {
+      Ops[0] = getConstant(Fold);
-        Ops[0] = getConstant(CI);
       Ops.erase(Ops.begin()+1);  // Erase the folded element
       if (Ops.size() == 1) return Ops[0];
       LHSC = cast<SCEVConstant>(Ops[0]);
-      } else {
-        // If we couldn't fold the expression, move to the next constant.  Note
-        // that this is impossible to happen in practice because we always
-        // constant fold constant ints to constant ints.
-        ++Idx;
-      }
     }
 
     // If we are left with a constant zero being added, strip it off.
@@ -950,19 +954,12 @@ SCEVHandle ScalarEvolution::getMulExpr(std::vector<SCEVHandle> &Ops) {
     ++Idx;
     while (SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {
       // We found two constants, fold them together!
-      Constant *Fold = ConstantInt::get(LHSC->getValue()->getValue() * 
+      ConstantInt *Fold = ConstantInt::get(LHSC->getValue()->getValue() * 
                                            RHSC->getValue()->getValue());
-      if (ConstantInt *CI = dyn_cast<ConstantInt>(Fold)) {
+      Ops[0] = getConstant(Fold);
-        Ops[0] = getConstant(CI);
       Ops.erase(Ops.begin()+1);  // Erase the folded element
       if (Ops.size() == 1) return Ops[0];
       LHSC = cast<SCEVConstant>(Ops[0]);
-      } else {
-        // If we couldn't fold the expression, move to the next constant.  Note
-        // that this is impossible to happen in practice because we always
-        // constant fold constant ints to constant ints.
-        ++Idx;
-      }
     }
 
     // If we are left with a constant one being multiplied, strip it off.
@@ -1170,20 +1167,13 @@ SCEVHandle ScalarEvolution::getSMaxExpr(std::vector<SCEVHandle> Ops) {
     assert(Idx < Ops.size());
     while (SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {
       // We found two constants, fold them together!
-      Constant *Fold = ConstantInt::get(
+      ConstantInt *Fold = ConstantInt::get(
                               APIntOps::smax(LHSC->getValue()->getValue(),
                                              RHSC->getValue()->getValue()));
-      if (ConstantInt *CI = dyn_cast<ConstantInt>(Fold)) {
+      Ops[0] = getConstant(Fold);
-        Ops[0] = getConstant(CI);
       Ops.erase(Ops.begin()+1);  // Erase the folded element
       if (Ops.size() == 1) return Ops[0];
       LHSC = cast<SCEVConstant>(Ops[0]);
-      } else {
-        // If we couldn't fold the expression, move to the next constant.  Note
-        // that this is impossible to happen in practice because we always
-        // constant fold constant ints to constant ints.
-        ++Idx;
-      }
     }
 
     // If we are left with a constant -inf, strip it off.
@@ -1226,7 +1216,7 @@ SCEVHandle ScalarEvolution::getSMaxExpr(std::vector<SCEVHandle> Ops) {
 
   assert(!Ops.empty() && "Reduced smax down to nothing!");
 
-  // Okay, it looks like we really DO need an add expr.  Check to see if we
+  // Okay, it looks like we really DO need an smax expr.  Check to see if we
   // already have one, otherwise create a new one.
   std::vector<SCEV*> SCEVOps(Ops.begin(), Ops.end());
   SCEVCommutativeExpr *&Result = (*SCEVCommExprs)[std::make_pair(scSMaxExpr,
@@ -1235,6 +1225,86 @@ SCEVHandle ScalarEvolution::getSMaxExpr(std::vector<SCEVHandle> Ops) {
   return Result;
 }
 
+SCEVHandle ScalarEvolution::getUMaxExpr(const SCEVHandle &LHS,
+                                        const SCEVHandle &RHS) {
+  std::vector<SCEVHandle> Ops;
+  Ops.push_back(LHS);
+  Ops.push_back(RHS);
+  return getUMaxExpr(Ops);
+}
+
+SCEVHandle ScalarEvolution::getUMaxExpr(std::vector<SCEVHandle> Ops) {
+  assert(!Ops.empty() && "Cannot get empty umax!");
+  if (Ops.size() == 1) return Ops[0];
+
+  // Sort by complexity, this groups all similar expression types together.
+  GroupByComplexity(Ops);
+
+  // If there are any constants, fold them together.
+  unsigned Idx = 0;
+  if (SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) {
+    ++Idx;
+    assert(Idx < Ops.size());
+    while (SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {
+      // We found two constants, fold them together!
+      ConstantInt *Fold = ConstantInt::get(
+                              APIntOps::umax(LHSC->getValue()->getValue(),
+                                             RHSC->getValue()->getValue()));
+      Ops[0] = getConstant(Fold);
+      Ops.erase(Ops.begin()+1);  // Erase the folded element
+      if (Ops.size() == 1) return Ops[0];
+      LHSC = cast<SCEVConstant>(Ops[0]);
+    }
+
+    // If we are left with a constant zero, strip it off.
+    if (cast<SCEVConstant>(Ops[0])->getValue()->isMinValue(false)) {
+      Ops.erase(Ops.begin());
+      --Idx;
+    }
+  }
+
+  if (Ops.size() == 1) return Ops[0];
+
+  // Find the first UMax
+  while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scUMaxExpr)
+    ++Idx;
+
+  // Check to see if one of the operands is a UMax. If so, expand its operands
+  // onto our operand list, and recurse to simplify.
+  if (Idx < Ops.size()) {
+    bool DeletedUMax = false;
+    while (SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(Ops[Idx])) {
+      Ops.insert(Ops.end(), UMax->op_begin(), UMax->op_end());
+      Ops.erase(Ops.begin()+Idx);
+      DeletedUMax = true;
+    }
+
+    if (DeletedUMax)
+      return getUMaxExpr(Ops);
+  }
+
+  // Okay, check to see if the same value occurs in the operand list twice.  If
+  // so, delete one.  Since we sorted the list, these values are required to
+  // be adjacent.
+  for (unsigned i = 0, e = Ops.size()-1; i != e; ++i)
+    if (Ops[i] == Ops[i+1]) {      //  X umax Y umax Y  -->  X umax Y
+      Ops.erase(Ops.begin()+i, Ops.begin()+i+1);
+      --i; --e;
+    }
+
+  if (Ops.size() == 1) return Ops[0];
+
+  assert(!Ops.empty() && "Reduced umax down to nothing!");
+
+  // Okay, it looks like we really DO need a umax expr.  Check to see if we
+  // already have one, otherwise create a new one.
+  std::vector<SCEV*> SCEVOps(Ops.begin(), Ops.end());
+  SCEVCommutativeExpr *&Result = (*SCEVCommExprs)[std::make_pair(scUMaxExpr,
+                                                                 SCEVOps)];
+  if (Result == 0) Result = new SCEVUMaxExpr(Ops);
+  return Result;
+}
+
 SCEVHandle ScalarEvolution::getUnknown(Value *V) {
   if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
     return getConstant(CI);
@@ -1606,6 +1676,14 @@ static uint32_t GetMinTrailingZeros(SCEVHandle S) {
     return MinOpRes;
   }
 
+  if (SCEVUMaxExpr *M = dyn_cast<SCEVUMaxExpr>(S)) {
+    // The result is the min of all operands results.
+    uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0));
+    for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i)
+      MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i)));
+    return MinOpRes;
+  }
+
   // SCEVUDivExpr, SCEVUnknown
   return 0;
 }
@@ -1653,6 +1731,8 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
         if (CI->getValue().isSignBit())
           return SE.getAddExpr(getSCEV(I->getOperand(0)),
                                getSCEV(I->getOperand(1)));
+        else if (CI->isAllOnesValue())
+          return SE.getNotSCEV(getSCEV(I->getOperand(0)));
       }
       break;
 
@@ -1686,7 +1766,8 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
       return createNodeForPHI(cast<PHINode>(I));
 
     case Instruction::Select:
-      // This could be an SCEVSMax that was lowered earlier. Try to recover it.
+      // This could be a smax or umax that was lowered earlier.
+      // Try to recover it.
       if (ICmpInst *ICI = dyn_cast<ICmpInst>(I->getOperand(0))) {
         Value *LHS = ICI->getOperand(0);
         Value *RHS = ICI->getOperand(1);
@@ -1699,6 +1780,25 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
         case ICmpInst::ICMP_SGE:
           if (LHS == I->getOperand(1) && RHS == I->getOperand(2))
             return SE.getSMaxExpr(getSCEV(LHS), getSCEV(RHS));
+          else if (LHS == I->getOperand(2) && RHS == I->getOperand(1))
+            // -smax(-x, -y) == smin(x, y).
+            return SE.getNegativeSCEV(SE.getSMaxExpr(
+                                          SE.getNegativeSCEV(getSCEV(LHS)),
+                                          SE.getNegativeSCEV(getSCEV(RHS))));
+          break;
+        case ICmpInst::ICMP_ULT:
+        case ICmpInst::ICMP_ULE:
+          std::swap(LHS, RHS);
+          // fall through
+        case ICmpInst::ICMP_UGT:
+        case ICmpInst::ICMP_UGE:
+          if (LHS == I->getOperand(1) && RHS == I->getOperand(2))
+            return SE.getUMaxExpr(getSCEV(LHS), getSCEV(RHS));
+          else if (LHS == I->getOperand(2) && RHS == I->getOperand(1))
+            // ~umax(~x, ~y) == umin(x, y)
+            return SE.getNotSCEV(SE.getUMaxExpr(SE.getNotSCEV(getSCEV(LHS)),
+                                                SE.getNotSCEV(getSCEV(RHS))));
+          break;
         default:
           break;
         }
@@ -2212,7 +2312,7 @@ SCEVHandle ScalarEvolutionsImpl::getSCEVAtScope(SCEV *V, const Loop *L) {
 
   if (isa<SCEVConstant>(V)) return V;
 
-  // If this instruction is evolves from a constant-evolving PHI, compute the
+  // If this instruction is evolved from a constant-evolving PHI, compute the
   // exit value from the loop without using SCEVs.
   if (SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V)) {
     if (Instruction *I = dyn_cast<Instruction>(SU->getValue())) {
@@ -2308,6 +2408,8 @@ SCEVHandle ScalarEvolutionsImpl::getSCEVAtScope(SCEV *V, const Loop *L) {
           return SE.getMulExpr(NewOps);
         if (isa<SCEVSMaxExpr>(Comm))
           return SE.getSMaxExpr(NewOps);
+        if (isa<SCEVUMaxExpr>(Comm))
+          return SE.getUMaxExpr(NewOps);
         assert(0 && "Unknown commutative SCEV type!");
       }
     }
@@ -2540,8 +2642,8 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L, bool isSigned) {
 
     // Then, we get the value of the LHS in the first iteration in which the
     // above condition doesn't hold.  This equals to max(m,n).
-    // FIXME (PR2003): we should have an "umax" operator as well.
+    SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start)
-    SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS,Start) : (SCEVHandle)RHS;
+                              : SE.getUMaxExpr(RHS, Start);
 
     // Finally, we subtract these two values to get the number of times the
     // backedge is executed: max(m,n)-n.

llvm/lib/Analysis/ScalarEvolutionExpander.cpp

@@ -220,6 +220,16 @@ Value *SCEVExpander::visitSMaxExpr(SCEVSMaxExpr *S) {
   return LHS;
 }
 
+Value *SCEVExpander::visitUMaxExpr(SCEVUMaxExpr *S) {
+  Value *LHS = expand(S->getOperand(0));
+  for (unsigned i = 1; i < S->getNumOperands(); ++i) {
+    Value *RHS = expand(S->getOperand(i));
+    Value *ICmp = new ICmpInst(ICmpInst::ICMP_UGT, LHS, RHS, "tmp", InsertPt);
+    LHS = new SelectInst(ICmp, LHS, RHS, "umax", InsertPt);
+  }
+  return LHS;
+}
+
 Value *SCEVExpander::expand(SCEV *S) {
   // Check to see if we already expanded this.
   std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S);
@@ -230,4 +240,3 @@ Value *SCEVExpander::expand(SCEV *S) {
   InsertedExpressions[S] = V;
   return V;
 }
-

llvm/test/Analysis/ScalarEvolution/2007-08-06-Unsigned.ll

@@ -1,4 +1,4 @@
-; RUN: llvm-as < %s | opt -scalar-evolution -analyze | grep {Loop bb: ( -1 + ( -1 \\*  %x) +  %y) iterations!}
+; RUN: llvm-as < %s | opt -scalar-evolution -analyze | grep {Loop bb: ( -1 + ( -1 \\*  %x) + (( 1 +  %x) umax  %y)) iterations!}
 ; PR1597
 
 define i32 @f(i32 %x, i32 %y) {

llvm/test/Analysis/ScalarEvolution/2008-02-15-UMax.ll

@@ -0,0 +1,17 @@
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution | grep umax
+; PR2003
+
+define i32 @foo(i32 %n) {
+entry:
+        br label %header
+header:
+        %i = phi i32 [ 100, %entry ], [ %i.inc, %next ]
+        %cond = icmp ult i32 %i, %n
+        br i1 %cond, label %next, label %return
+next:
+        %i.inc = add i32 %i, 1
+        br label %header
+return:
+        ret i32 %i
+}
+