[TargetLowering] SimplifyDemandedBits - use DemandedElts to better identify partial splat shift amounts

llvm-svn: 364541

1 files changed, 21 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 74ab96afe5a..50cd8cded62 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1040,20 +1040,23 @@ bool TargetLowering::SimplifyDemandedBits(
     SDValue Op0 = Op.getOperand(0);
     SDValue Op1 = Op.getOperand(1);
 
-    if (ConstantSDNode *SA = isConstOrConstSplat(Op1)) {
+    if (ConstantSDNode *SA = isConstOrConstSplat(Op1, DemandedElts)) {
       // If the shift count is an invalid immediate, don't do anything.
       if (SA->getAPIntValue().uge(BitWidth))
         break;
 
       unsigned ShAmt = SA->getZExtValue();
+      if (ShAmt == 0)
+        return TLO.CombineTo(Op, Op0);
 
       // If this is ((X >>u C1) << ShAmt), see if we can simplify this into a
       // single shift.  We can do this if the bottom bits (which are shifted
       // out) are never demanded.
+      // TODO - support non-uniform vector amounts.
       if (Op0.getOpcode() == ISD::SRL) {
-        if (ShAmt &&
-            (DemandedBits & APInt::getLowBitsSet(BitWidth, ShAmt)) == 0) {
-          if (ConstantSDNode *SA2 = isConstOrConstSplat(Op0.getOperand(1))) {
+        if ((DemandedBits & APInt::getLowBitsSet(BitWidth, ShAmt)) == 0) {
+          if (ConstantSDNode *SA2 =
+                  isConstOrConstSplat(Op0.getOperand(1), DemandedElts)) {
             if (SA2->getAPIntValue().ult(BitWidth)) {
               unsigned C1 = SA2->getZExtValue();
               unsigned Opc = ISD::SHL;
@@ -1134,13 +1137,16 @@ bool TargetLowering::SimplifyDemandedBits(
     SDValue Op0 = Op.getOperand(0);
     SDValue Op1 = Op.getOperand(1);
 
-    if (ConstantSDNode *SA = isConstOrConstSplat(Op1)) {
+    if (ConstantSDNode *SA = isConstOrConstSplat(Op1, DemandedElts)) {
       // If the shift count is an invalid immediate, don't do anything.
       if (SA->getAPIntValue().uge(BitWidth))
         break;
 
-      EVT ShiftVT = Op1.getValueType();
       unsigned ShAmt = SA->getZExtValue();
+      if (ShAmt == 0)
+        return TLO.CombineTo(Op, Op0);
+
+      EVT ShiftVT = Op1.getValueType();
       APInt InDemandedMask = (DemandedBits << ShAmt);
 
       // If the shift is exact, then it does demand the low bits (and knows that
@@ -1151,10 +1157,11 @@ bool TargetLowering::SimplifyDemandedBits(
       // If this is ((X << C1) >>u ShAmt), see if we can simplify this into a
       // single shift.  We can do this if the top bits (which are shifted out)
       // are never demanded.
+      // TODO - support non-uniform vector amounts.
       if (Op0.getOpcode() == ISD::SHL) {
-        if (ConstantSDNode *SA2 = isConstOrConstSplat(Op0.getOperand(1))) {
-          if (ShAmt &&
-              (DemandedBits & APInt::getHighBitsSet(BitWidth, ShAmt)) == 0) {
+        if (ConstantSDNode *SA2 =
+                isConstOrConstSplat(Op0.getOperand(1), DemandedElts)) {
+          if ((DemandedBits & APInt::getHighBitsSet(BitWidth, ShAmt)) == 0) {
             if (SA2->getAPIntValue().ult(BitWidth)) {
               unsigned C1 = SA2->getZExtValue();
               unsigned Opc = ISD::SRL;
@@ -1195,12 +1202,15 @@ bool TargetLowering::SimplifyDemandedBits(
     if (DemandedBits.isOneValue())
       return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, dl, VT, Op0, Op1));
 
-    if (ConstantSDNode *SA = isConstOrConstSplat(Op1)) {
+    if (ConstantSDNode *SA = isConstOrConstSplat(Op1, DemandedElts)) {
       // If the shift count is an invalid immediate, don't do anything.
       if (SA->getAPIntValue().uge(BitWidth))
         break;
 
       unsigned ShAmt = SA->getZExtValue();
+      if (ShAmt == 0)
+        return TLO.CombineTo(Op, Op0);
+
       APInt InDemandedMask = (DemandedBits << ShAmt);
 
       // If the shift is exact, then it does demand the low bits (and knows that
@@ -1251,7 +1261,7 @@ bool TargetLowering::SimplifyDemandedBits(
     SDValue Op2 = Op.getOperand(2);
     bool IsFSHL = (Op.getOpcode() == ISD::FSHL);
 
-    if (ConstantSDNode *SA = isConstOrConstSplat(Op2)) {
+    if (ConstantSDNode *SA = isConstOrConstSplat(Op2, DemandedElts)) {
       unsigned Amt = SA->getAPIntValue().urem(BitWidth);
 
       // For fshl, 0-shift returns the 1st arg.