[llvm] r321056 - [X86] Remove dead code for turning vector shifts by large amounts into a zero vector.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Mon Dec 18 21:21:50 2017
New Revision: 321056

URL: http://llvm.org/viewvc/llvm-project?rev=321056&view=rev
Log:
[X86] Remove dead code for turning vector shifts by large amounts into a zero vector.

Pretty sure these are handled by a target independent DAG combine that turns them into undef these days.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=321056&r1=321055&r2=321056&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Mon Dec 18 21:21:50 2017
@@ -32622,37 +32622,6 @@ static SDValue combineShiftRightLogical(
   return SDValue();
 }
 
-/// \brief Returns a vector of 0s if the node in input is a vector logical
-/// shift by a constant amount which is known to be bigger than or equal
-/// to the vector element size in bits.
-static SDValue performShiftToAllZeros(SDNode *N, SelectionDAG &DAG,
-                                      const X86Subtarget &Subtarget) {
-  EVT VT = N->getValueType(0);
-
-  if (VT != MVT::v2i64 && VT != MVT::v4i32 && VT != MVT::v8i16 &&
-      (!Subtarget.hasInt256() ||
-       (VT != MVT::v4i64 && VT != MVT::v8i32 && VT != MVT::v16i16)))
-    return SDValue();
-
-  SDValue Amt = N->getOperand(1);
-  SDLoc DL(N);
-  if (auto *AmtBV = dyn_cast<BuildVectorSDNode>(Amt))
-    if (auto *AmtSplat = AmtBV->getConstantSplatNode()) {
-      const APInt &ShiftAmt = AmtSplat->getAPIntValue();
-      unsigned MaxAmount =
-        VT.getSimpleVT().getScalarSizeInBits();
-
-      // SSE2/AVX2 logical shifts always return a vector of 0s
-      // if the shift amount is bigger than or equal to
-      // the element size. The constant shift amount will be
-      // encoded as a 8-bit immediate.
-      if (ShiftAmt.trunc(8).uge(MaxAmount))
-        return getZeroVector(VT.getSimpleVT(), Subtarget, DAG, DL);
-    }
-
-  return SDValue();
-}
-
 static SDValue combineShift(SDNode* N, SelectionDAG &DAG,
                             TargetLowering::DAGCombinerInfo &DCI,
                             const X86Subtarget &Subtarget) {
@@ -32668,11 +32637,6 @@ static SDValue combineShift(SDNode* N, S
     if (SDValue V = combineShiftRightLogical(N, DAG))
       return V;
 
-  // Try to fold this logical shift into a zero vector.
-  if (N->getOpcode() != ISD::SRA)
-    if (SDValue V = performShiftToAllZeros(N, DAG, Subtarget))
-      return V;
-
   return SDValue();
 }