[x86] use getSignBit() for clarity; NFCI

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294333 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index b34313862521f432e8d68628900fcdcb65cb2aec..3bf1ffdc6000314c644fe226b62da17d51f32f9d 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -29477,8 +29477,8 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
 
   // If this is a *dynamic* select (non-constant condition) and we can match
   // this node with one of the variable blend instructions, restructure the
-  // condition so that the blends can use the high bit of each element and use
-  // SimplifyDemandedBits to simplify the condition operand.
+  // condition so that blends can use the high (sign) bit of each element and
+  // use SimplifyDemandedBits to simplify the condition operand.
   if (N->getOpcode() == ISD::VSELECT && DCI.isBeforeLegalizeOps() &&
       !DCI.isBeforeLegalize() &&
       !ISD::isBuildVectorOfConstantSDNodes(Cond.getNode())) {
@@ -29513,8 +29513,7 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
       return SDValue();
 
     assert(BitWidth >= 8 && BitWidth <= 64 && "Invalid mask size");
-    APInt DemandedMask = APInt::getHighBitsSet(BitWidth, 1);
-
+    APInt DemandedMask(APInt::getSignBit(BitWidth));
     APInt KnownZero, KnownOne;
     TargetLowering::TargetLoweringOpt TLO(DAG, DCI.isBeforeLegalize(),
                                           DCI.isBeforeLegalizeOps());