Reimplement r114460 in target-independent DAGCombine rather than target-dependent, by using

the predicate to discover the number of sign bits.  Enhance X86's target lowering to provide
a useful response to this query.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114473 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 29 insertions, 23 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c71b3c0cad..1bd1e00fcd 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1424,6 +1424,20 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
                                        N0.getOperand(0).getOperand(1),
                                        N0.getOperand(1)));
 
+  if (N1.getOpcode() == ISD::AND) {
+    SDValue AndOp0 = N1.getOperand(0);
+    ConstantSDNode *AndOp1 = dyn_cast<ConstantSDNode>(N1->getOperand(1)); 
+    unsigned NumSignBits = DAG.ComputeNumSignBits(AndOp0);
+    unsigned DestBits = VT.getScalarType().getSizeInBits();
+    
+    // (add z, (and (sbbl x, x), 1)) -> (sub z, (sbbl x, x))
+    // and similar xforms where the inner op is either ~0 or 0.
+    if (NumSignBits == DestBits && AndOp1 && AndOp1->isOne()) {
+      DebugLoc DL = N->getDebugLoc();
+      return DAG.getNode(ISD::SUB, DL, VT, N->getOperand(0), AndOp0);
+    }
+  }
+
   return SDValue();
 }
 
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index ad9ef77a9d..ab57353ba1 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -1021,7 +1021,6 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
   setTargetDAGCombine(ISD::OR);
   setTargetDAGCombine(ISD::STORE);
   setTargetDAGCombine(ISD::ZERO_EXTEND);
-  setTargetDAGCombine(ISD::ADD);
   if (Subtarget->is64Bit())
     setTargetDAGCombine(ISD::MUL);
 
@@ -9980,6 +9979,16 @@ void X86TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
   }
 }
 
+unsigned X86TargetLowering::ComputeNumSignBitsForTargetNode(SDValue Op,
+                                                         unsigned Depth) const {
+  // SETCC_CARRY sets the dest to ~0 for true or 0 for false.
+  if (Op.getOpcode() == X86ISD::SETCC_CARRY)
+    return Op.getValueType().getScalarType().getSizeInBits();
+  
+  // Fallback case.
+  return 1;
+}
+
 /// isGAPlusOffset - Returns true (and the GlobalValue and the offset) if the
 /// node is a GlobalAddress + offset.
 bool X86TargetLowering::isGAPlusOffset(SDNode *N,
@@ -10454,27 +10463,6 @@ static SDValue PerformCMOVCombine(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
-/// PerformAddCombine - Optimize ADD when combined with X86 opcodes.
-static SDValue PerformAddCombine(SDNode *N, SelectionDAG &DAG,
-                                 TargetLowering::DAGCombinerInfo &DCI) {
-  if (DCI.isBeforeLegalize() || DCI.isCalledByLegalizer())
-    return SDValue();
-  
-  EVT VT = N->getValueType(0);
-  SDValue Op1 = N->getOperand(1);
-  if (Op1->getOpcode() == ISD::AND) {
-    SDValue AndOp0 = Op1->getOperand(0);
-    ConstantSDNode *AndOp1 = dyn_cast<ConstantSDNode>(Op1->getOperand(1)); 
-    // (add z, (and (sbbl x, x), 1)) -> (sub z, (sbbl x, x))
-    if (AndOp0->getOpcode() == X86ISD::SETCC_CARRY &&
-        AndOp1 && AndOp1->getZExtValue() == 1) {
-      DebugLoc DL = N->getDebugLoc();
-      return DAG.getNode(ISD::SUB, DL, VT, N->getOperand(0), AndOp0);
-    }
-  }
-  
-  return SDValue();
-}
 
 /// PerformMulCombine - Optimize a single multiply with constant into two
 /// in order to implement it with two cheaper instructions, e.g.
@@ -10961,7 +10949,6 @@ SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
                         return PerformEXTRACT_VECTOR_ELTCombine(N, DAG, *this);
   case ISD::SELECT:         return PerformSELECTCombine(N, DAG, Subtarget);
   case X86ISD::CMOV:        return PerformCMOVCombine(N, DAG, DCI);
-  case ISD::ADD:            return PerformAddCombine(N, DAG, DCI);
   case ISD::MUL:            return PerformMulCombine(N, DAG, DCI);
   case ISD::SHL:
   case ISD::SRA:
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index 6e6f25c93a..9bb5f64b56 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -523,6 +523,11 @@ namespace llvm {
                                                 const SelectionDAG &DAG,
                                                 unsigned Depth = 0) const;
 
+    // ComputeNumSignBitsForTargetNode - Determine the number of bits in the
+    // operation that are sign bits.
+    virtual unsigned ComputeNumSignBitsForTargetNode(SDValue Op,
+                                                     unsigned Depth) const;
+
     virtual bool
     isGAPlusOffset(SDNode *N, const GlobalValue* &GA, int64_t &Offset) const;