[NFC][X86] combineX86ShuffleChain(): rename inner Mask to avoid future shadowing

I want to hoist `Mask` variable higher up,
but then it would clash with this one.
So let's rename this one first.

There are no other intentional changes here other than said rename.

Author: LebedevRI

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -35889,22 +35889,23 @@ static SDValue combineX86ShuffleChain(ArrayRef<SDValue> Inputs, SDValue Root,
     }
 
     // Narrow shuffle mask to v4x128.
-    SmallVector<int, 4> Mask;
+    SmallVector<int, 4> ScaledMask;
     assert((BaseMaskEltSizeInBits % 128) == 0 && "Illegal mask size");
-    narrowShuffleMaskElts(BaseMaskEltSizeInBits / 128, BaseMask, Mask);
+    narrowShuffleMaskElts(BaseMaskEltSizeInBits / 128, BaseMask, ScaledMask);
 
     // Try to lower to vshuf64x2/vshuf32x4.
-    auto MatchSHUF128 = [&](MVT ShuffleVT, const SDLoc &DL, ArrayRef<int> Mask,
-                            SDValue V1, SDValue V2, SelectionDAG &DAG) {
+    auto MatchSHUF128 = [&](MVT ShuffleVT, const SDLoc &DL,
+                            ArrayRef<int> ScaledMask, SDValue V1, SDValue V2,
+                            SelectionDAG &DAG) {
       unsigned PermMask = 0;
       // Insure elements came from the same Op.
       SDValue Ops[2] = {DAG.getUNDEF(ShuffleVT), DAG.getUNDEF(ShuffleVT)};
       for (int i = 0; i < 4; ++i) {
-        assert(Mask[i] >= -1 && "Illegal shuffle sentinel value");
-        if (Mask[i] < 0)
+        assert(ScaledMask[i] >= -1 && "Illegal shuffle sentinel value");
+        if (ScaledMask[i] < 0)
           continue;
 
-        SDValue Op = Mask[i] >= 4 ? V2 : V1;
+        SDValue Op = ScaledMask[i] >= 4 ? V2 : V1;
         unsigned OpIndex = i / 2;
         if (Ops[OpIndex].isUndef())
           Ops[OpIndex] = Op;
@@ -35914,7 +35915,7 @@ static SDValue combineX86ShuffleChain(ArrayRef<SDValue> Inputs, SDValue Root,
         // Convert the 128-bit shuffle mask selection values into 128-bit
         // selection bits defined by a vshuf64x2 instruction's immediate control
         // byte.
-        PermMask |= (Mask[i] % 4) << (i * 2);
+        PermMask |= (ScaledMask[i] % 4) << (i * 2);
       }
 
       return DAG.getNode(X86ISD::SHUF128, DL, ShuffleVT,
@@ -35926,18 +35927,20 @@ static SDValue combineX86ShuffleChain(ArrayRef<SDValue> Inputs, SDValue Root,
     // FIXME: Is there a better way to do this? is256BitLaneRepeatedShuffleMask
     // doesn't work because our mask is for 128 bits and we don't have an MVT
     // to match that.
-    bool PreferPERMQ =
-        UnaryShuffle && isUndefOrInRange(Mask[0], 0, 2) &&
-        isUndefOrInRange(Mask[1], 0, 2) && isUndefOrInRange(Mask[2], 2, 4) &&
-        isUndefOrInRange(Mask[3], 2, 4) &&
-        (Mask[0] < 0 || Mask[2] < 0 || Mask[0] == (Mask[2] % 2)) &&
-        (Mask[1] < 0 || Mask[3] < 0 || Mask[1] == (Mask[3] % 2));
-
-    if (!isAnyZero(Mask) && !PreferPERMQ) {
+    bool PreferPERMQ = UnaryShuffle && isUndefOrInRange(ScaledMask[0], 0, 2) &&
+                       isUndefOrInRange(ScaledMask[1], 0, 2) &&
+                       isUndefOrInRange(ScaledMask[2], 2, 4) &&
+                       isUndefOrInRange(ScaledMask[3], 2, 4) &&
+                       (ScaledMask[0] < 0 || ScaledMask[2] < 0 ||
+                        ScaledMask[0] == (ScaledMask[2] % 2)) &&
+                       (ScaledMask[1] < 0 || ScaledMask[3] < 0 ||
+                        ScaledMask[1] == (ScaledMask[3] % 2));
+
+    if (!isAnyZero(ScaledMask) && !PreferPERMQ) {
       if (Depth == 0 && Root.getOpcode() == X86ISD::SHUF128)
         return SDValue(); // Nothing to do!
       MVT ShuffleVT = (FloatDomain ? MVT::v8f64 : MVT::v8i64);
-      if (SDValue V = MatchSHUF128(ShuffleVT, DL, Mask, V1, V2, DAG))
+      if (SDValue V = MatchSHUF128(ShuffleVT, DL, ScaledMask, V1, V2, DAG))
         return DAG.getBitcast(RootVT, V);
     }
   }