[SelectionDAG] Add a signed integer absolute ISD node

Reduced version of D26357 - based on the discussion on llvm-dev about canonicalization of UMIN/UMAX/SMIN/SMAX as well as ABS I've reduced that patch to just the ABS ISD node (with x86/sse support) to improve basic combines and lowering.

ARM/AArch64, Hexagon, PowerPC and NVPTX all have similar instructions allowing us to make this a generic opcode and move away from the hard coded tablegen patterns which makes it tricky to match more complex patterns.

At the moment this patch doesn't attempt legalization as we only create an ABS node if its legal/custom.

Differential Revision: https://reviews.llvm.org/D29639

llvm-svn: 297780

4 files changed, 41 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 788b52d..0fe1eda 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -262,6 +262,7 @@ namespace {
     SDValue visitSRA(SDNode *N);
     SDValue visitSRL(SDNode *N);
     SDValue visitRotate(SDNode *N);
+    SDValue visitABS(SDNode *N);
     SDValue visitBSWAP(SDNode *N);
     SDValue visitBITREVERSE(SDNode *N);
     SDValue visitCTLZ(SDNode *N);
@@ -1423,6 +1424,7 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::SRL:                return visitSRL(N);
   case ISD::ROTR:
   case ISD::ROTL:               return visitRotate(N);
+  case ISD::ABS:                return visitABS(N);
   case ISD::BSWAP:              return visitBSWAP(N);
   case ISD::BITREVERSE:         return visitBITREVERSE(N);
   case ISD::CTLZ:               return visitCTLZ(N);
@@ -5004,6 +5006,17 @@ SDValue DAGCombiner::visitXOR(SDNode *N) {
                                          N01C->getAPIntValue(), DL, VT));
     }
   }
+
+  // fold Y = sra (X, size(X)-1); xor (add (X, Y), Y) -> (abs X)
+  unsigned OpSizeInBits = VT.getScalarSizeInBits();
+  if (N0.getOpcode() == ISD::ADD && N0.getOperand(1) == N1 &&
+      N1.getOpcode() == ISD::SRA && N1.getOperand(0) == N0.getOperand(0) &&
+      TLI.isOperationLegalOrCustom(ISD::ABS, VT)) {
+    if (ConstantSDNode *C = isConstOrConstSplat(N1.getOperand(1)))
+      if (C->getAPIntValue() == (OpSizeInBits - 1))
+        return DAG.getNode(ISD::ABS, SDLoc(N), VT, N0.getOperand(0));
+  }
+
   // fold (xor x, x) -> 0
   if (N0 == N1)
     return tryFoldToZero(SDLoc(N), TLI, VT, DAG, LegalOperations, LegalTypes);
@@ -5746,6 +5759,22 @@ SDValue DAGCombiner::visitSRL(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitABS(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  EVT VT = N->getValueType(0);
+
+  // fold (abs c1) -> c2
+  if (DAG.isConstantIntBuildVectorOrConstantInt(N0))
+    return DAG.getNode(ISD::ABS, SDLoc(N), VT, N0);
+  // fold (abs (abs x)) -> (abs x)
+  if (N0.getOpcode() == ISD::ABS)
+    return N0;
+  // fold (abs x) -> x iff not-negative
+  if (DAG.SignBitIsZero(N0))
+    return N0;
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitBSWAP(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   EVT VT = N->getValueType(0);
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 4f33eef..aed422a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3336,6 +3336,9 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
       if (VT == MVT::f128 && C->getValueType(0) == MVT::i128)
         return getConstantFP(APFloat(APFloat::IEEEquad(), Val), DL, VT);
       break;
+    case ISD::ABS:
+      return getConstant(Val.abs(), DL, VT, C->isTargetOpcode(),
+                         C->isOpaque());
     case ISD::BITREVERSE:
       return getConstant(Val.reverseBits(), DL, VT, C->isTargetOpcode(),
                          C->isOpaque());
@@ -3455,6 +3458,7 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
       case ISD::TRUNCATE:
       case ISD::UINT_TO_FP:
       case ISD::SINT_TO_FP:
+      case ISD::ABS:
       case ISD::BITREVERSE:
       case ISD::BSWAP:
       case ISD::CTLZ:
@@ -3572,6 +3576,12 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     }
     if (OpOpcode == ISD::UNDEF)
       return getUNDEF(VT);
+      break;
+  case ISD::ABS:
+    assert(VT.isInteger() && VT == Operand.getValueType() &&
+           "Invalid ABS!");
+    if (OpOpcode == ISD::UNDEF)
+      return getUNDEF(VT);
     break;
   case ISD::BSWAP:
     assert(VT.isInteger() && VT == Operand.getValueType() &&
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
index ba9ec68..488c60a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
@@ -300,6 +300,7 @@ std::string SDNode::getOperationName(const SelectionDAG *G) const {
   case ISD::GET_DYNAMIC_AREA_OFFSET:    return "get.dynamic.area.offset";
 
   // Bit manipulation
+  case ISD::ABS:                        return "abs";
   case ISD::BITREVERSE:                 return "bitreverse";
   case ISD::BSWAP:                      return "bswap";
   case ISD::CTPOP:                      return "ctpop";
diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index 518417d..7a2d50e 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -900,6 +900,7 @@ void TargetLoweringBase::initActions() {
     setOperationAction(ISD::SMAX, VT, Expand);
     setOperationAction(ISD::UMIN, VT, Expand);
     setOperationAction(ISD::UMAX, VT, Expand);
+    setOperationAction(ISD::ABS, VT, Expand);
 
     // Overflow operations default to expand
     setOperationAction(ISD::SADDO, VT, Expand);