[ValueTracking] Extract isKnownPositive [NFCI]

Extract out a generic interface from a recently landed patch and document a TODO in case compile time becomes a problem.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@263062 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ValueTracking.h

@@ -92,6 +92,13 @@ namespace llvm {
                           const Instruction *CxtI = nullptr,
                           const DominatorTree *DT = nullptr);
 
+  /// Returns true if the given value is known be positive (i.e. non-negative
+  /// and non-zero).
+  bool isKnownPositive(Value *V, const DataLayout &DL, unsigned Depth = 0,
+                       AssumptionCache *AC = nullptr,
+                       const Instruction *CxtI = nullptr,
+                       const DominatorTree *DT = nullptr);
+
   /// isKnownNonEqual - Return true if the given values are known to be
   /// non-equal when defined. Supports scalar integer types only.
   bool isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL,

lib/Analysis/ValueTracking.cpp

@@ -182,6 +182,18 @@ bool llvm::isKnownNonNegative(Value *V, const DataLayout &DL, unsigned Depth,
   return NonNegative;
 }
 
+bool llvm::isKnownPositive(Value *V, const DataLayout &DL, unsigned Depth,
+                           AssumptionCache *AC, const Instruction *CxtI,
+                           const DominatorTree *DT) {
+  if (auto *CI = dyn_cast<ConstantInt>(V))
+    return CI->getValue().isStrictlyPositive();
+
+  // TODO: We'd doing two recursive queries here.  We should factor this such
+  // that only a single query is needed.
+  return isKnownNonNegative(V, DL, Depth, AC, CxtI, DT) &&
+    isKnownNonZero(V, DL, Depth, AC, CxtI, DT);
+}
+
 static bool isKnownNonEqual(Value *V1, Value *V2, const Query &Q);
 
 bool llvm::isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL,

lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -3178,9 +3178,9 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
       if (auto *SI = dyn_cast<SelectInst>(Op0)) {
         SelectPatternResult SPR = matchSelectPattern(SI, A, B);
         if (SPR.Flavor == SPF_SMIN) {
-          if (isKnownNonNegative(A, DL) && isKnownNonZero(A, DL))
+          if (isKnownPositive(A, DL))
             return new ICmpInst(I.getPredicate(), B, CI);
-          if (isKnownNonNegative(B, DL) && isKnownNonZero(B, DL))
+          if (isKnownPositive(B, DL))
             return new ICmpInst(I.getPredicate(), A, CI);
         }
       }