[X86] combineVectorSizedSetCCEquality - convert to mayFoldIntoVector helper (llvm#172215)

Add AssumeSingleUse (default = false) argument to mayFoldIntoVector to
allow us to match combineVectorSizedSetCCEquality behaviour with
AssumeSingleUse=true

Hopefully we can drop the AssumeSingleUse entirely soon, but there are a
number of messy test regressions that need handling first

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -2860,12 +2860,13 @@ bool X86::mayFoldIntoZeroExtend(SDValue Op) {
 }
 
 // Return true if its cheap to bitcast this to a vector type.
-static bool mayFoldIntoVector(SDValue Op, const X86Subtarget &Subtarget) {
+static bool mayFoldIntoVector(SDValue Op, const X86Subtarget &Subtarget,
+                              bool AssumeSingleUse = false) {
   if (peekThroughBitcasts(Op).getValueType().isVector())
     return true;
   if (isa<ConstantSDNode>(Op) || isa<ConstantFPSDNode>(Op))
     return true;
-  return X86::mayFoldLoad(Op, Subtarget, /*AssumeSingleUse=*/false,
+  return X86::mayFoldLoad(Op, Subtarget, AssumeSingleUse,
                           /*IgnoreAlignment=*/true);
 }
 
@@ -23122,12 +23123,9 @@ static SDValue combineVectorSizedSetCCEquality(EVT VT, SDValue X, SDValue Y,
     return SDValue();
 
   // Don't perform this combine if constructing the vector will be expensive.
-  auto IsVectorBitCastCheap = [](SDValue X) {
-    X = peekThroughBitcasts(X);
-    return isa<ConstantSDNode>(X) || X.getValueType().isVector() ||
-           ISD::isNormalLoad(X.getNode());
-  };
-  if ((!IsVectorBitCastCheap(X) || !IsVectorBitCastCheap(Y)) &&
+  // TODO: Drop AssumeSingleUse = true override.
+  if ((!mayFoldIntoVector(X, Subtarget, /*AssumeSingleUse=*/true) ||
+       !mayFoldIntoVector(Y, Subtarget, /*AssumeSingleUse=*/true)) &&
       !IsOrXorXorTreeCCZero)
     return SDValue();