[llvm] [SPIR-V] Align memory scopes with SPIR-V specification and LLVM expectations and change default mem scope value (PR #108528)

[Matt Arsenault via llvm-commits]

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@@ -847,25 +852,18 @@ bool SPIRVInstructionSelector::selectBitcast(Register ResVReg,
 
 static SPIRV::Scope::Scope getScope(SyncScope::ID Ord,
                                     const SyncScopeIDs &SSIDs) {
-  if (Ord == SyncScope::SingleThread || Ord == SSIDs.Work_ItemSSID)
+  if (Ord == SyncScope::SingleThread)
     return SPIRV::Scope::Invocation;
-  else if (Ord == SyncScope::System || Ord == SSIDs.DeviceSSID)
-    return SPIRV::Scope::Device;
-  else if (Ord == SSIDs.WorkGroupSSID)
-    return SPIRV::Scope::Workgroup;
-  else if (Ord == SSIDs.AllSVMDevicesSSID)
-    return SPIRV::Scope::CrossDevice;
-  else if (Ord == SSIDs.SubGroupSSID)
+  if (Ord == SSIDs.SubGroupSSID)
     return SPIRV::Scope::Subgroup;
-  else
-    // OpenCL approach is: "The functions that do not have memory_scope argument
-    // have the same semantics as the corresponding functions with the
-    // memory_scope argument set to memory_scope_device." See ref.: //
-    // https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_C.html#atomic-functions
-    // In our case if the scope is unknown, assuming that SPIR-V code is to be
-    // consumed in an OpenCL environment, we use the same approach and set the
-    // scope to memory_scope_device.
+  if (Ord == SSIDs.WorkGroupSSID)
+    return SPIRV::Scope::Workgroup;
+  if (Ord == SSIDs.DeviceSSID)
     return SPIRV::Scope::Device;
+  if (Ord == SyncScope::System)
+    return SPIRV::Scope::CrossDevice;
+  // Use the most conservative/safe choice as the default.
+  return SPIRV::Scope::CrossDevice;
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arsenm wrote:

I'd expect this to also be caught by an explicit Ord == SyncScope::System above where the other generic ID is handled 

https://github.com/llvm/llvm-project/pull/108528