[SCEV] Add explicit representations of umin/smin

Summary:
Currently we express umin as `~umax(~x, ~y)`. However, this becomes
a problem for operands in non-integral pointer spaces, because `~x`
is not something we can compute for `x` non-integral. However, since
comparisons are generally still allowed, we are actually able to
express `umin(x, y)` directly as long as we don't try to express is
as a umax. Support this by adding an explicit umin/smin representation
to SCEV. We do this by factoring the existing getUMax/getSMax functions
into a new function that does all four. The previous two functions were
largely identical.

Reviewed By: sanjoy
Differential Revision: https://reviews.llvm.org/D50167

llvm-svn: 360159

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -598,6 +598,8 @@ class ScalarEvolution {
   /// \p IndexExprs The expressions for the indices.
   const SCEV *getGEPExpr(GEPOperator *GEP,
                          const SmallVectorImpl<const SCEV *> &IndexExprs);
+  const SCEV *getMinMaxExpr(unsigned Kind,
+                            SmallVectorImpl<const SCEV *> &Operands);
   const SCEV *getSMaxExpr(const SCEV *LHS, const SCEV *RHS);
   const SCEV *getSMaxExpr(SmallVectorImpl<const SCEV *> &Operands);
   const SCEV *getUMaxExpr(const SCEV *LHS, const SCEV *RHS);

llvm/include/llvm/Analysis/ScalarEvolutionExpander.h

@@ -367,6 +367,10 @@ namespace llvm {
 
     Value *visitUMaxExpr(const SCEVUMaxExpr *S);
 
+    Value *visitSMinExpr(const SCEVSMinExpr *S);
+
+    Value *visitUMinExpr(const SCEVUMinExpr *S);
+
     Value *visitUnknown(const SCEVUnknown *S) {
       return S->getValue();
     }

llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h

@@ -39,7 +39,7 @@ class Type;
     // These should be ordered in terms of increasing complexity to make the
     // folders simpler.
     scConstant, scTruncate, scZeroExtend, scSignExtend, scAddExpr, scMulExpr,
-    scUDivExpr, scAddRecExpr, scUMaxExpr, scSMaxExpr,
+    scUDivExpr, scAddRecExpr, scUMaxExpr, scSMaxExpr, scUMinExpr, scSMinExpr,
     scUnknown, scCouldNotCompute
   };
 
@@ -190,10 +190,9 @@ class Type;
 
     /// Methods for support type inquiry through isa, cast, and dyn_cast:
     static bool classof(const SCEV *S) {
-      return S->getSCEVType() == scAddExpr ||
-             S->getSCEVType() == scMulExpr ||
-             S->getSCEVType() == scSMaxExpr ||
-             S->getSCEVType() == scUMaxExpr ||
+      return S->getSCEVType() == scAddExpr || S->getSCEVType() == scMulExpr ||
+             S->getSCEVType() == scSMaxExpr || S->getSCEVType() == scUMaxExpr ||
+             S->getSCEVType() == scSMinExpr || S->getSCEVType() == scUMinExpr ||
              S->getSCEVType() == scAddRecExpr;
     }
   };
@@ -208,10 +207,9 @@ class Type;
   public:
     /// Methods for support type inquiry through isa, cast, and dyn_cast:
     static bool classof(const SCEV *S) {
-      return S->getSCEVType() == scAddExpr ||
-             S->getSCEVType() == scMulExpr ||
-             S->getSCEVType() == scSMaxExpr ||
-             S->getSCEVType() == scUMaxExpr;
+      return S->getSCEVType() == scAddExpr || S->getSCEVType() == scMulExpr ||
+             S->getSCEVType() == scSMaxExpr || S->getSCEVType() == scUMaxExpr ||
+             S->getSCEVType() == scSMinExpr || S->getSCEVType() == scUMinExpr;
     }
 
     /// Set flags for a non-recurrence without clearing previously set flags.
@@ -366,17 +364,53 @@ class Type;
     }
   };
 
-  /// This class represents a signed maximum selection.
-  class SCEVSMaxExpr : public SCEVCommutativeExpr {
+  /// This node is the base class min/max selections.
+  class SCEVMinMaxExpr : public SCEVCommutativeExpr {
     friend class ScalarEvolution;
 
-    SCEVSMaxExpr(const FoldingSetNodeIDRef ID,
-                 const SCEV *const *O, size_t N)
-      : SCEVCommutativeExpr(ID, scSMaxExpr, O, N) {
-      // Max never overflows.
+    static bool isMinMaxType(enum SCEVTypes T) {
+      return T == scSMaxExpr || T == scUMaxExpr || T == scSMinExpr ||
+             T == scUMinExpr;
+    }
+
+  protected:
+    /// Note: Constructing subclasses via this constructor is allowed
+    SCEVMinMaxExpr(const FoldingSetNodeIDRef ID, enum SCEVTypes T,
+                   const SCEV *const *O, size_t N)
+        : SCEVCommutativeExpr(ID, T, O, N) {
+      assert(isMinMaxType(T));
+      // Min and max never overflow
       setNoWrapFlags((NoWrapFlags)(FlagNUW | FlagNSW));
     }
 
+  public:
+    static bool classof(const SCEV *S) {
+      return isMinMaxType(static_cast<SCEVTypes>(S->getSCEVType()));
+    }
+
+    static enum SCEVTypes negate(enum SCEVTypes T) {
+      switch (T) {
+      case scSMaxExpr:
+        return scSMinExpr;
+      case scSMinExpr:
+        return scSMaxExpr;
+      case scUMaxExpr:
+        return scUMinExpr;
+      case scUMinExpr:
+        return scUMaxExpr;
+      default:
+        llvm_unreachable("Not a min or max SCEV type!");
+      }
+    }
+  };
+
+  /// This class represents a signed maximum selection.
+  class SCEVSMaxExpr : public SCEVMinMaxExpr {
+    friend class ScalarEvolution;
+
+    SCEVSMaxExpr(const FoldingSetNodeIDRef ID, const SCEV *const *O, size_t N)
+        : SCEVMinMaxExpr(ID, scSMaxExpr, O, N) {}
+
   public:
     /// Methods for support type inquiry through isa, cast, and dyn_cast:
     static bool classof(const SCEV *S) {
@@ -385,15 +419,11 @@ class Type;
   };
 
   /// This class represents an unsigned maximum selection.
-  class SCEVUMaxExpr : public SCEVCommutativeExpr {
+  class SCEVUMaxExpr : public SCEVMinMaxExpr {
     friend class ScalarEvolution;
 
-    SCEVUMaxExpr(const FoldingSetNodeIDRef ID,
-                 const SCEV *const *O, size_t N)
-      : SCEVCommutativeExpr(ID, scUMaxExpr, O, N) {
-      // Max never overflows.
-      setNoWrapFlags((NoWrapFlags)(FlagNUW | FlagNSW));
-    }
+    SCEVUMaxExpr(const FoldingSetNodeIDRef ID, const SCEV *const *O, size_t N)
+        : SCEVMinMaxExpr(ID, scUMaxExpr, O, N) {}
 
   public:
     /// Methods for support type inquiry through isa, cast, and dyn_cast:
@@ -402,6 +432,34 @@ class Type;
     }
   };
 
+  /// This class represents a signed minimum selection.
+  class SCEVSMinExpr : public SCEVMinMaxExpr {
+    friend class ScalarEvolution;
+
+    SCEVSMinExpr(const FoldingSetNodeIDRef ID, const SCEV *const *O, size_t N)
+        : SCEVMinMaxExpr(ID, scSMinExpr, O, N) {}
+
+  public:
+    /// Methods for support type inquiry through isa, cast, and dyn_cast:
+    static bool classof(const SCEV *S) {
+      return S->getSCEVType() == scSMinExpr;
+    }
+  };
+
+  /// This class represents an unsigned minimum selection.
+  class SCEVUMinExpr : public SCEVMinMaxExpr {
+    friend class ScalarEvolution;
+
+    SCEVUMinExpr(const FoldingSetNodeIDRef ID, const SCEV *const *O, size_t N)
+        : SCEVMinMaxExpr(ID, scUMinExpr, O, N) {}
+
+  public:
+    /// Methods for support type inquiry through isa, cast, and dyn_cast:
+    static bool classof(const SCEV *S) {
+      return S->getSCEVType() == scUMinExpr;
+    }
+  };
+
   /// This means that we are dealing with an entirely unknown SCEV
   /// value, and only represent it as its LLVM Value.  This is the
   /// "bottom" value for the analysis.
@@ -474,6 +532,10 @@ class Type;
         return ((SC*)this)->visitSMaxExpr((const SCEVSMaxExpr*)S);
       case scUMaxExpr:
         return ((SC*)this)->visitUMaxExpr((const SCEVUMaxExpr*)S);
+      case scSMinExpr:
+        return ((SC *)this)->visitSMinExpr((const SCEVSMinExpr *)S);
+      case scUMinExpr:
+        return ((SC *)this)->visitUMinExpr((const SCEVUMinExpr *)S);
       case scUnknown:
         return ((SC*)this)->visitUnknown((const SCEVUnknown*)S);
       case scCouldNotCompute:
@@ -527,6 +589,8 @@ class Type;
         case scMulExpr:
         case scSMaxExpr:
         case scUMaxExpr:
+        case scSMinExpr:
+        case scUMinExpr:
         case scAddRecExpr:
           for (const auto *Op : cast<SCEVNAryExpr>(S)->operands())
             push(Op);
@@ -689,6 +753,26 @@ class Type;
       return !Changed ? Expr : SE.getUMaxExpr(Operands);
     }
 
+    const SCEV *visitSMinExpr(const SCEVSMinExpr *Expr) {
+      SmallVector<const SCEV *, 2> Operands;
+      bool Changed = false;
+      for (auto *Op : Expr->operands()) {
+        Operands.push_back(((SC *)this)->visit(Op));
+        Changed |= Op != Operands.back();
+      }
+      return !Changed ? Expr : SE.getSMinExpr(Operands);
+    }
+
+    const SCEV *visitUMinExpr(const SCEVUMinExpr *Expr) {
+      SmallVector<const SCEV *, 2> Operands;
+      bool Changed = false;
+      for (auto *Op : Expr->operands()) {
+        Operands.push_back(((SC *)this)->visit(Op));
+        Changed |= Op != Operands.back();
+      }
+      return !Changed ? Expr : SE.getUMinExpr(Operands);
+    }
+
     const SCEV *visitUnknown(const SCEVUnknown *Expr) {
       return Expr;
     }