[llvm] [DXIL] Add GroupMemoryBarrierWithGroupSync intrinsic (PR #114349)

[Finn Plummer via llvm-commits]

================
@@ -294,6 +294,43 @@ class Attributes<Version ver = DXIL1_0, list<DXILAttribute> attrs> {
   list<DXILAttribute> op_attrs = attrs;
 }
 
+class DXILConstant<int value_> {
+  int value = value_;
+}
+
+defset list<DXILConstant> BarrierModes = {
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inbelic wrote:

Following from here: https://github.com/llvm/llvm-project/pull/111884#discussion_r1813994789.

We could also do:
```
defvar BarrierMode_DeviceMemoryBarrier = 2;
...
defvar BarrierMode_AllMemoryBarrierWithGroupSync = 11;
```
without needing to define the `DXILConstant` class and the list. I suppose you no longer have the concreting grouping and scope of the definitions, but I think the potential simplicity it will give to the `Arg` class and hence `DXILEmitter`, would be worth it.

https://github.com/llvm/llvm-project/pull/114349