Analysis: Reformulate WillNotOverflowUnsignedAdd for reusability

WillNotOverflowUnsignedAdd's smarts will live in ValueTracking as
computeOverflowForUnsignedAdd.  It now returns a tri-state result:
never overflows, always overflows and sometimes overflows.

llvm-svn: 225329

llvm/include/llvm/Analysis/ValueTracking.h

@@ -221,6 +221,11 @@ namespace llvm {
                                                AssumptionCache *AC,
                                                const Instruction *CxtI,
                                                const DominatorTree *DT);
+  OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
+                                               const DataLayout *DL,
+                                               AssumptionCache *AC,
+                                               const Instruction *CxtI,
+                                               const DominatorTree *DT);
 } // end namespace llvm
 
 #endif

llvm/lib/Analysis/ValueTracking.cpp

@@ -2729,3 +2729,32 @@ OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
 
   return OverflowResult::MayOverflow;
 }
+
+OverflowResult llvm::computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
+                                                   const DataLayout *DL,
+                                                   AssumptionCache *AC,
+                                                   const Instruction *CxtI,
+                                                   const DominatorTree *DT) {
+  bool LHSKnownNonNegative, LHSKnownNegative;
+  ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
+                 AC, CxtI, DT);
+  if (LHSKnownNonNegative || LHSKnownNegative) {
+    bool RHSKnownNonNegative, RHSKnownNegative;
+    ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
+                   AC, CxtI, DT);
+
+    if (LHSKnownNegative && RHSKnownNegative) {
+      // The sign bit is set in both cases: this MUST overflow.
+      // Create a simple add instruction, and insert it into the struct.
+      return OverflowResult::AlwaysOverflows;
+    }
+
+    if (LHSKnownNonNegative && RHSKnownNonNegative) {
+      // The sign bit is clear in both cases: this CANNOT overflow.
+      // Create a simple add instruction, and insert it into the struct.
+      return OverflowResult::NeverOverflows;
+    }
+  }
+
+  return OverflowResult::MayOverflow;
+}

llvm/lib/Transforms/InstCombine/InstCombine.h

@@ -282,7 +282,6 @@ private:
                                  bool DoXform = true);
   Instruction *transformSExtICmp(ICmpInst *ICI, Instruction &CI);
   bool WillNotOverflowSignedAdd(Value *LHS, Value *RHS, Instruction *CxtI);
-  bool WillNotOverflowUnsignedAdd(Value *LHS, Value *RHS, Instruction *CxtI);
   bool WillNotOverflowSignedSub(Value *LHS, Value *RHS, Instruction *CxtI);
   bool WillNotOverflowUnsignedSub(Value *LHS, Value *RHS, Instruction *CxtI);
   bool WillNotOverflowSignedMul(Value *LHS, Value *RHS, Instruction *CxtI);
@@ -391,6 +390,10 @@ public:
                                                const Instruction *CxtI) {
     return llvm::computeOverflowForUnsignedMul(LHS, RHS, DL, AC, CxtI, DT);
   }
+  OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
+                                               const Instruction *CxtI) {
+    return llvm::computeOverflowForUnsignedAdd(LHS, RHS, DL, AC, CxtI, DT);
+  }
 
 private:
   /// SimplifyAssociativeOrCommutative - This performs a few simplifications for

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -937,22 +937,6 @@ bool InstCombiner::WillNotOverflowSignedAdd(Value *LHS, Value *RHS,
   return false;
 }
 
-/// WillNotOverflowUnsignedAdd - Return true if we can prove that:
-///    (zext (add LHS, RHS))  === (add (zext LHS), (zext RHS))
-bool InstCombiner::WillNotOverflowUnsignedAdd(Value *LHS, Value *RHS,
-                                              Instruction *CxtI) {
-  // There are different heuristics we can use for this. Here is a simple one.
-  // If the sign bit of LHS and that of RHS are both zero, no unsigned wrap.
-  bool LHSKnownNonNegative, LHSKnownNegative;
-  bool RHSKnownNonNegative, RHSKnownNegative;
-  ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, /*Depth=*/0, CxtI);
-  ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, /*Depth=*/0, CxtI);
-  if (LHSKnownNonNegative && RHSKnownNonNegative)
-    return true;
-
-  return false;
-}
-
 /// \brief Return true if we can prove that:
 ///    (sub LHS, RHS)  === (sub nsw LHS, RHS)
 /// This basically requires proving that the add in the original type would not
@@ -1327,7 +1311,9 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
     Changed = true;
     I.setHasNoSignedWrap(true);
   }
-  if (!I.hasNoUnsignedWrap() && WillNotOverflowUnsignedAdd(LHS, RHS, &I)) {
+  if (!I.hasNoUnsignedWrap() &&
+      computeOverflowForUnsignedAdd(LHS, RHS, &I) ==
+          OverflowResult::NeverOverflows) {
     Changed = true;
     I.setHasNoUnsignedWrap(true);
   }

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -352,33 +352,11 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     break;
   case Intrinsic::uadd_with_overflow: {
     Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
-    IntegerType *IT = cast<IntegerType>(II->getArgOperand(0)->getType());
-    uint32_t BitWidth = IT->getBitWidth();
-    APInt LHSKnownZero(BitWidth, 0);
-    APInt LHSKnownOne(BitWidth, 0);
-    computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, 0, II);
-    bool LHSKnownNegative = LHSKnownOne[BitWidth - 1];
-    bool LHSKnownPositive = LHSKnownZero[BitWidth - 1];
-
-    if (LHSKnownNegative || LHSKnownPositive) {
-      APInt RHSKnownZero(BitWidth, 0);
-      APInt RHSKnownOne(BitWidth, 0);
-      computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, 0, II);
-      bool RHSKnownNegative = RHSKnownOne[BitWidth - 1];
-      bool RHSKnownPositive = RHSKnownZero[BitWidth - 1];
-      if (LHSKnownNegative && RHSKnownNegative) {
-        // The sign bit is set in both cases: this MUST overflow.
-        // Create a simple add instruction, and insert it into the struct.
-        return CreateOverflowTuple(II, Builder->CreateAdd(LHS, RHS), true,
-                                    /*ReUseName*/true);
-      }
-
-      if (LHSKnownPositive && RHSKnownPositive) {
-        // The sign bit is clear in both cases: this CANNOT overflow.
-        // Create a simple add instruction, and insert it into the struct.
-        return CreateOverflowTuple(II, Builder->CreateNUWAdd(LHS, RHS), false);
-      }
-    }
+    OverflowResult OR = computeOverflowForUnsignedAdd(LHS, RHS, II);
+    if (OR == OverflowResult::NeverOverflows)
+      return CreateOverflowTuple(II, Builder->CreateNUWAdd(LHS, RHS), false);
+    if (OR == OverflowResult::AlwaysOverflows)
+      return CreateOverflowTuple(II, Builder->CreateAdd(LHS, RHS), true);
   }
   // FALL THROUGH uadd into sadd
   case Intrinsic::sadd_with_overflow: