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- Fix comment so that it describes how the code really works:

Browse Source 
// fold (or (shl x, (*ext y)), (srl x, (*ext (sub 32, y)))) ->
   //   (rotl x, y)
   // fold (or (shl x, (*ext y)), (srl x, (*ext (sub 32, y)))) ->
   //   (rotr x, (sub 32, y))

Example: (x == 0xDEADBEEF and y == 4)

    (x << 4) | (x >> 28)
 => 0xEADBEEF0 | 0x0000000D
 => 0xEADBEEFD

    (rotl x, 4)
 => 0xEADBEEFD

    (rotr x, 28)
 => 0xEADBEEFD

- Fix comment and code for second version. It wasn't using the rot* propertly.

   // fold (or (shl x, (*ext (sub 32, y))), (srl x, (*ext r))) -> 
   //   (rotr x, y)
   // fold (or (shl x, (*ext (sub 32, y))), (srl x, (*ext r))) ->
   //   (rotl x, (sub 32, y))

    (x << 28) | (x >> 4)
 => 0xD0000000 | 0x0DEADBEE
 => 0xDDEADBEE

    (rotl x, 4)
 => 0xEADBEEFD

    (rotr x, 28)
 => (0xEADBEEFD)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55575 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2008-08-31 00:37:27 +00:00
parent dc71563794
commit c5cbda12e9
1 changed files with 6 additions and 6 deletions
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12
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -2064,9 +2064,9 @@ SDNode *DAGCombiner::MatchRotate(SDValue LHS, SDValue RHS) {
if (RExtOp0.getOpcode() == ISD::SUB &&
RExtOp0.getOperand(1) == LExtOp0) {
// fold (or (shl x, (*ext y)), (srl x, (*ext (sub 32, y)))) ->
// (rotr x, y)
// (rotl x, y)
// fold (or (shl x, (*ext y)), (srl x, (*ext (sub 32, y)))) ->
// (rotl x, (sub 32, y))
// (rotr x, (sub 32, y))
if (ConstantSDNode *SUBC = cast<ConstantSDNode>(RExtOp0.getOperand(0))) {
if (SUBC->getAPIntValue() == OpSizeInBits) {
return DAG.getNode(HasROTL ? ISD::ROTL : ISD::ROTR, VT, LHSShiftArg,
@ -2076,13 +2076,13 @@ SDNode *DAGCombiner::MatchRotate(SDValue LHS, SDValue RHS) {
} else if (LExtOp0.getOpcode() == ISD::SUB &&
RExtOp0 == LExtOp0.getOperand(1)) {
// fold (or (shl x, (*ext (sub 32, y))), (srl x, (*ext r))) ->
// (rotl x, y)
// (rotr x, y)
// fold (or (shl x, (*ext (sub 32, y))), (srl x, (*ext r))) ->
// (rotr x, (sub 32, y))
// (rotl x, (sub 32, y))
if (ConstantSDNode *SUBC = cast<ConstantSDNode>(LExtOp0.getOperand(0))) {
if (SUBC->getAPIntValue() == OpSizeInBits) {
return DAG.getNode(ISD::ROTL, VT, LHSShiftArg,
HasROTL ? RHSShiftAmt : LHSShiftAmt).getNode();
return DAG.getNode(HasROTL ? ISD::ROTL : ISD::ROTR, VT, LHSShiftArg,
HasROTL ? LHSShiftAmt : RHSShiftAmt).getNode();
}
}
}