[PATCH] D31795: [ARM] Remove redundant computeKnownBits helper.

[Eli Friedman via Phabricator via llvm-commits]

efriedma created this revision.
Herald added a subscriber: aemerson.

Move the BFI logic to computeKnownBitsForTargetNode, and delete the redundant CMOV logic.

This is intended as a cleanup, but it's probably possible to construct a case where moving the BFI logic allows more combines.


Repository:
  rL LLVM

https://reviews.llvm.org/D31795

Files:
  lib/Target/ARM/ARMISelLowering.cpp


Index: lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- lib/Target/ARM/ARMISelLowering.cpp
+++ lib/Target/ARM/ARMISelLowering.cpp
@@ -11688,34 +11688,6 @@
   return SDValue();
 }
 
-static void computeKnownBits(SelectionDAG &DAG, SDValue Op, APInt &KnownZero,
-                             APInt &KnownOne) {
-  if (Op.getOpcode() == ARMISD::BFI) {
-    // Conservatively, we can recurse down the first operand
-    // and just mask out all affected bits.
-    computeKnownBits(DAG, Op.getOperand(0), KnownZero, KnownOne);
-
-    // The operand to BFI is already a mask suitable for removing the bits it
-    // sets.
-    ConstantSDNode *CI = cast<ConstantSDNode>(Op.getOperand(2));
-    const APInt &Mask = CI->getAPIntValue();
-    KnownZero &= Mask;
-    KnownOne &= Mask;
-    return;
-  }
-  if (Op.getOpcode() == ARMISD::CMOV) {
-    APInt KZ2(KnownZero.getBitWidth(), 0);
-    APInt KO2(KnownOne.getBitWidth(), 0);
-    computeKnownBits(DAG, Op.getOperand(0), KnownZero, KnownOne);
-    computeKnownBits(DAG, Op.getOperand(1), KZ2, KO2);
-
-    KnownZero &= KZ2;
-    KnownOne &= KO2;
-    return;
-  }
-  return DAG.computeKnownBits(Op, KnownZero, KnownOne);
-}
-
 SDValue ARMTargetLowering::PerformCMOVToBFICombine(SDNode *CMOV, SelectionDAG &DAG) const {
   // If we have a CMOV, OR and AND combination such as:
   //   if (x & CN)
@@ -11777,7 +11749,7 @@
   // Lastly, can we determine that the bits defined by OrCI
   // are zero in Y?
   APInt KnownZero, KnownOne;
-  computeKnownBits(DAG, Y, KnownZero, KnownOne);
+  DAG.computeKnownBits(Y, KnownZero, KnownOne);
   if ((OrCI & KnownZero) != OrCI)
     return SDValue();
 
@@ -12657,6 +12629,19 @@
     }
     }
   }
+  case ARMISD::BFI: {
+    // Conservatively, we can recurse down the first operand
+    // and just mask out all affected bits.
+    DAG.computeKnownBits(Op.getOperand(0), KnownZero, KnownOne);
+
+    // The operand to BFI is already a mask suitable for removing the bits it
+    // sets.
+    ConstantSDNode *CI = cast<ConstantSDNode>(Op.getOperand(2));
+    const APInt &Mask = CI->getAPIntValue();
+    KnownZero &= Mask;
+    KnownOne &= Mask;
+    return;
+  }
   }
 }
 


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