1 files changed, 44 insertions, 30 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index d10046c..05e702f 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -136,6 +136,18 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
         Value *NewShl = Builder->CreateShl(XorLHS, ShAmt, "sext");
         return BinaryOperator::CreateAShr(NewShl, ShAmt);
       }
+
+      // If this is a xor that was canonicalized from a sub, turn it back into
+      // a sub and fuse this add with it.
+      if (LHS->hasOneUse() && (XorRHS->getValue()+1).isPowerOf2()) {
+        IntegerType *IT = cast<IntegerType>(I.getType());
+        APInt LHSKnownOne(IT->getBitWidth(), 0);
+        APInt LHSKnownZero(IT->getBitWidth(), 0);
+        ComputeMaskedBits(XorLHS, LHSKnownZero, LHSKnownOne);
+        if ((XorRHS->getValue() | LHSKnownZero).isAllOnesValue())
+          return BinaryOperator::CreateSub(ConstantExpr::getAdd(XorRHS, CI),
+                                           XorLHS);
+      }
     }
   }
 
@@ -189,14 +201,13 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
 
   // A+B --> A|B iff A and B have no bits set in common.
   if (IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
-    APInt Mask = APInt::getAllOnesValue(IT->getBitWidth());
     APInt LHSKnownOne(IT->getBitWidth(), 0);
     APInt LHSKnownZero(IT->getBitWidth(), 0);
-    ComputeMaskedBits(LHS, Mask, LHSKnownZero, LHSKnownOne);
+    ComputeMaskedBits(LHS, LHSKnownZero, LHSKnownOne);
     if (LHSKnownZero != 0) {
       APInt RHSKnownOne(IT->getBitWidth(), 0);
       APInt RHSKnownZero(IT->getBitWidth(), 0);
-      ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
+      ComputeMaskedBits(RHS, RHSKnownZero, RHSKnownOne);
       
       // No bits in common -> bitwise or.
       if ((LHSKnownZero|RHSKnownZero).isAllOnesValue())
@@ -466,57 +477,57 @@ Value *InstCombiner::OptimizePointerDifference(Value *LHS, Value *RHS,
   // If LHS is a gep based on RHS or RHS is a gep based on LHS, we can optimize
   // this.
   bool Swapped = false;
-  GetElementPtrInst *GEP = 0;
-  ConstantExpr *CstGEP = 0;
-  
-  // TODO: Could also optimize &A[i] - &A[j] -> "i-j", and "&A.foo[i] - &A.foo".
+  GEPOperator *GEP1 = 0, *GEP2 = 0;
+
   // For now we require one side to be the base pointer "A" or a constant
-  // expression derived from it.
-  if (GetElementPtrInst *LHSGEP = dyn_cast<GetElementPtrInst>(LHS)) {
+  // GEP derived from it.
+  if (GEPOperator *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
     // (gep X, ...) - X
     if (LHSGEP->getOperand(0) == RHS) {
-      GEP = LHSGEP;
+      GEP1 = LHSGEP;
       Swapped = false;
-    } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(RHS)) {
-      // (gep X, ...) - (ce_gep X, ...)
-      if (CE->getOpcode() == Instruction::GetElementPtr &&
-          LHSGEP->getOperand(0) == CE->getOperand(0)) {
-        CstGEP = CE;
-        GEP = LHSGEP;
+    } else if (GEPOperator *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
+      // (gep X, ...) - (gep X, ...)
+      if (LHSGEP->getOperand(0)->stripPointerCasts() ==
+            RHSGEP->getOperand(0)->stripPointerCasts()) {
+        GEP2 = RHSGEP;
+        GEP1 = LHSGEP;
         Swapped = false;
       }
     }
   }
   
-  if (GetElementPtrInst *RHSGEP = dyn_cast<GetElementPtrInst>(RHS)) {
+  if (GEPOperator *RHSGEP = dyn_cast<GEPOperator>(RHS)) {
     // X - (gep X, ...)
     if (RHSGEP->getOperand(0) == LHS) {
-      GEP = RHSGEP;
+      GEP1 = RHSGEP;
       Swapped = true;
-    } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(LHS)) {
-      // (ce_gep X, ...) - (gep X, ...)
-      if (CE->getOpcode() == Instruction::GetElementPtr &&
-          RHSGEP->getOperand(0) == CE->getOperand(0)) {
-        CstGEP = CE;
-        GEP = RHSGEP;
+    } else if (GEPOperator *LHSGEP = dyn_cast<GEPOperator>(LHS)) {
+      // (gep X, ...) - (gep X, ...)
+      if (RHSGEP->getOperand(0)->stripPointerCasts() ==
+            LHSGEP->getOperand(0)->stripPointerCasts()) {
+        GEP2 = LHSGEP;
+        GEP1 = RHSGEP;
         Swapped = true;
       }
     }
   }
   
-  if (GEP == 0)
+  // Avoid duplicating the arithmetic if GEP2 has non-constant indices and
+  // multiple users.
+  if (GEP1 == 0 ||
+      (GEP2 != 0 && !GEP2->hasAllConstantIndices() && !GEP2->hasOneUse()))
     return 0;
   
   // Emit the offset of the GEP and an intptr_t.
-  Value *Result = EmitGEPOffset(GEP);
+  Value *Result = EmitGEPOffset(GEP1);
   
   // If we had a constant expression GEP on the other side offsetting the
   // pointer, subtract it from the offset we have.
-  if (CstGEP) {
-    Value *CstOffset = EmitGEPOffset(CstGEP);
-    Result = Builder->CreateSub(Result, CstOffset);
+  if (GEP2) {
+    Value *Offset = EmitGEPOffset(GEP2);
+    Result = Builder->CreateSub(Result, Offset);
   }
-  
 
   // If we have p - gep(p, ...)  then we have to negate the result.
   if (Swapped)
@@ -587,6 +598,9 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
     ConstantInt *C2;
     if (match(Op1, m_Add(m_Value(X), m_ConstantInt(C2))))
       return BinaryOperator::CreateSub(ConstantExpr::getSub(C, C2), X);
+
+    if (SimplifyDemandedInstructionBits(I))
+      return &I;
   }