[llvm-commits] [llvm] r55575 - /llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

[Bill Wendling]

Author: void
Date: Sat Aug 30 19:37:27 2008
New Revision: 55575

URL: http://llvm.org/viewvc/llvm-project?rev=55575&view=rev
Log:
- Fix comment so that it describes how the code really works:

   // 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)

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=55575&r1=55574&r2=55575&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Sat Aug 30 19:37:27 2008
@@ -2064,9 +2064,9 @@
     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 @@
     } 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();
         }
       }
     }