[x86] use getSplatIndex() in lowerShuffleAsBroadcast()

The old code was doing an N^2 search for splat index.

Differential Revision: https://reviews.llvm.org/D74064

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -28,6 +28,7 @@
 #include "llvm/Analysis/BlockFrequencyInfo.h"
 #include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/Analysis/VectorUtils.h"
 #include "llvm/CodeGen/IntrinsicLowering.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -12725,23 +12726,14 @@ static SDValue lowerShuffleAsBroadcast(const SDLoc &DL, MVT VT, SDValue V1,
 
   // With MOVDDUP (v2f64) we can broadcast from a register or a load, otherwise
   // we can only broadcast from a register with AVX2.
-  unsigned NumElts = Mask.size();
   unsigned NumEltBits = VT.getScalarSizeInBits();
   unsigned Opcode = (VT == MVT::v2f64 && !Subtarget.hasAVX2())
                         ? X86ISD::MOVDDUP
                         : X86ISD::VBROADCAST;
   bool BroadcastFromReg = (Opcode == X86ISD::MOVDDUP) || Subtarget.hasAVX2();
 
   // Check that the mask is a broadcast.
-  int BroadcastIdx = -1;
-  for (int i = 0; i != (int)NumElts; ++i) {
-    SmallVector<int, 8> BroadcastMask(NumElts, i);
-    if (isShuffleEquivalent(V1, V2, Mask, BroadcastMask)) {
-      BroadcastIdx = i;
-      break;
-    }
-  }
-
+  int BroadcastIdx = getSplatIndex(Mask);
   if (BroadcastIdx < 0)
     return SDValue();
   assert(BroadcastIdx < (int)Mask.size() && "We only expect to be called with "