[llvm] [SelectionDAG] Add SelectionDAG::getTypeSize. NFC (PR #169764)

[Sander de Smalen via llvm-commits]

================
@@ -2098,32 +2083,41 @@ SDValue SelectionDAG::getCondCode(ISD::CondCode Cond) {
   return SDValue(CondCodeNodes[Cond], 0);
 }
 
-SDValue SelectionDAG::getVScale(const SDLoc &DL, EVT VT, APInt MulImm,
-                                bool ConstantFold) {
+SDValue SelectionDAG::getVScale(const SDLoc &DL, EVT VT, APInt MulImm) {
   assert(MulImm.getBitWidth() == VT.getSizeInBits() &&
          "APInt size does not match type size!");
 
   if (MulImm == 0)
     return getConstant(0, DL, VT);
 
-  if (ConstantFold) {
-    const MachineFunction &MF = getMachineFunction();
-    const Function &F = MF.getFunction();
-    ConstantRange CR = getVScaleRange(&F, 64);
-    if (const APInt *C = CR.getSingleElement())
-      return getConstant(MulImm * C->getZExtValue(), DL, VT);
-  }
+  const MachineFunction &MF = getMachineFunction();
+  const Function &F = MF.getFunction();
+  ConstantRange CR = getVScaleRange(&F, 64);
+  if (const APInt *C = CR.getSingleElement())
+    return getConstant(MulImm * C->getZExtValue(), DL, VT);
 
   return getNode(ISD::VSCALE, DL, VT, getConstant(MulImm, DL, VT));
 }
 
-SDValue SelectionDAG::getElementCount(const SDLoc &DL, EVT VT, ElementCount EC,
-                                      bool ConstantFold) {
-  if (EC.isScalable())
-    return getVScale(DL, VT,
-                     APInt(VT.getSizeInBits(), EC.getKnownMinValue()));
+/// \returns a value of type \p VT that represents the runtime value of \p X,
----------------
sdesmalen-arm wrote:

nit: 
```suggestion
/// \returns a value of type \p VT that represents the runtime value of \p Quantity,
```

maybe also say that this can only be an ElementCount or a TypeSize?

https://github.com/llvm/llvm-project/pull/169764