[InstCombine] Provide a way to calculate KnownZero/One for Add/Sub in SimplifyDemande...

SimplifyDemandedUseBits for Add/Sub already recursed down LHS and RHS for simplifying bits. If that didn't provide any simplifications we fall back to calling computeKnownBits which will recurse again. Instead just take the known bits for LHS and RHS we already have and call into a new function in ValueTracking that can calculate the known bits given the LHS/RHS bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298711 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/ValueTracking.h b/include/llvm/Analysis/ValueTracking.h
index e3c2f3bed2277537c90fb51a5240eb5f66d78991..08b6f300bc5c45e8d77893f87db58f4fe13f8aa9 100644 (file)
--- a/include/llvm/Analysis/ValueTracking.h
+++ b/include/llvm/Analysis/ValueTracking.h
@@ -55,6 +55,11 @@ template <typename T> class ArrayRef;
                         const Instruction *CxtI = nullptr,
                         const DominatorTree *DT = nullptr,
                         OptimizationRemarkEmitter *ORE = nullptr);
+  /// Compute known bits for add/sub using LHS/RHS known bits.
+  void computeKnownBitsForAddSub(bool Add, bool NSW,
+                                 APInt &KnownZero, APInt &KnownOne,
+                                 APInt &LHSKnownZero, APInt &LHSKnownOne,
+                                 APInt &RHSKnownZero, APInt &RHSKnownOne);
   /// Compute known bits from the range metadata.
   /// \p KnownZero the set of bits that are known to be zero
   /// \p KnownOne the set of bits that are known to be one

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 6f043666cefbb1dcb80c32a691ba883bd3f39a1b..eeb6d49b6a48b91c221d625c80ac2e9c7b260090 100644 (file)
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -250,37 +250,29 @@ unsigned llvm::ComputeNumSignBits(const Value *V, const DataLayout &DL,
   return ::ComputeNumSignBits(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT));
 }
 
-static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
-                                   bool NSW,
-                                   APInt &KnownZero, APInt &KnownOne,
-                                   APInt &KnownZero2, APInt &KnownOne2,
-                                   unsigned Depth, const Query &Q) {
-  unsigned BitWidth = KnownZero.getBitWidth();
-
-  // If an initial sequence of bits in the result is not needed, the
-  // corresponding bits in the operands are not needed.
-  APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
-  computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, Depth + 1, Q);
-  computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q);
-
+/// Compute known bits for add/sub using LHS/RHS known bits.
+void llvm::computeKnownBitsForAddSub(bool Add, bool NSW,
+                                     APInt &KnownZero, APInt &KnownOne,
+                                     APInt &LHSKnownZero, APInt &LHSKnownOne,
+                                     APInt &RHSKnownZero, APInt &RHSKnownOne) {
   // Carry in a 1 for a subtract, rather than a 0.
   uint64_t CarryIn = 0;
   if (!Add) {
     // Sum = LHS + ~RHS + 1
-    std::swap(KnownZero2, KnownOne2);
+    std::swap(RHSKnownZero, RHSKnownOne);
     CarryIn = 1;
   }
 
-  APInt PossibleSumZero = ~LHSKnownZero + ~KnownZero2 + CarryIn;
-  APInt PossibleSumOne = LHSKnownOne + KnownOne2 + CarryIn;
+  APInt PossibleSumZero = ~LHSKnownZero + ~RHSKnownZero + CarryIn;
+  APInt PossibleSumOne = LHSKnownOne + RHSKnownOne + CarryIn;
 
   // Compute known bits of the carry.
-  APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ KnownZero2);
-  APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ KnownOne2;
+  APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ RHSKnownZero);
+  APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ RHSKnownOne;
 
   // Compute set of known bits (where all three relevant bits are known).
   APInt LHSKnown = LHSKnownZero | LHSKnownOne;
-  APInt RHSKnown = KnownZero2 | KnownOne2;
+  APInt RHSKnown = RHSKnownZero | RHSKnownOne;
   APInt CarryKnown = CarryKnownZero | CarryKnownOne;
   APInt Known = LHSKnown & RHSKnown & CarryKnown;
 
@@ -296,14 +288,36 @@ static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
     if (NSW) {
       // Adding two non-negative numbers, or subtracting a negative number from
       // a non-negative one, can't wrap into negative.
-      if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
+      if (LHSKnownZero.isNegative() && RHSKnownZero.isNegative())
         KnownZero.setSignBit();
       // Adding two negative numbers, or subtracting a non-negative number from
       // a negative one, can't wrap into non-negative.
-      else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
+      else if (LHSKnownOne.isNegative() && RHSKnownOne.isNegative())
         KnownOne.setSignBit();
     }
   }
+
+  // Put the RHS/LHS back how we found them.
+  if (!Add) {
+    std::swap(RHSKnownZero, RHSKnownOne);
+  }
+}
+
+static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
+                                   bool NSW,
+                                   APInt &KnownZero, APInt &KnownOne,
+                                   APInt &KnownZero2, APInt &KnownOne2,
+                                   unsigned Depth, const Query &Q) {
+  unsigned BitWidth = KnownZero.getBitWidth();
+
+  // If an initial sequence of bits in the result is not needed, the
+  // corresponding bits in the operands are not needed.
+  APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
+  computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, Depth + 1, Q);
+  computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q);
+
+  computeKnownBitsForAddSub(Add, NSW, KnownZero, KnownOne, LHSKnownZero,
+                            LHSKnownOne, KnownZero2, KnownOne2);
 }
 
 static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 41d4a4820bf31ef70d77983a29009faf7f78c876..d10fa06f0c2e85c06d1f883b446177fa4c6c7d88 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -538,7 +538,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
                                LHSKnownZero, LHSKnownOne, Depth + 1) ||
           ShrinkDemandedConstant(I, 1, DemandedFromOps) ||
           SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
-                               LHSKnownZero, LHSKnownOne, Depth + 1)) {
+                               RHSKnownZero, RHSKnownOne, Depth + 1)) {
         // Disable the nsw and nuw flags here: We can no longer guarantee that
         // we won't wrap after simplification. Removing the nsw/nuw flags is
         // legal here because the top bit is not demanded.
@@ -549,9 +549,10 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       }
     }
 
-    // Otherwise just hand the add/sub off to computeKnownBits to fill in
-    // the known zeros and ones.
-    computeKnownBits(V, KnownZero, KnownOne, Depth, CxtI);
+    // Otherwise compute the known bits using the RHS/LHS known bits.
+    bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
+    computeKnownBitsForAddSub(V, NSW, KnownZero, KnownOne, LHSKnownZero,
+                              LHSKnownOne, RHSKnownZero, RHSKnownOne);
     break;
   }
   case Instruction::Shl: