[llvm] [SPIR-V] Add support for HLSL SV_GroupIndex (PR #130670)

[Steven Perron via llvm-commits]

================
@@ -4005,6 +4017,40 @@ bool SPIRVInstructionSelector::loadVec3BuiltinInputID(
   return Result && MIB.constrainAllUses(TII, TRI, RBI);
 }
 
+// Generate the instructions to load 32-bit integer builtin input IDs/Indices.
+// Like LocalInvocationIndex
+bool SPIRVInstructionSelector::loadBuiltinInputID(
+    SPIRV::BuiltIn::BuiltIn BuiltInValue, Register ResVReg,
+    const SPIRVType *ResType, MachineInstr &I) const {
+  MachineIRBuilder MIRBuilder(I);
+  const SPIRVType *PtrType = GR.getOrCreateSPIRVPointerType(
+      ResType, MIRBuilder, SPIRV::StorageClass::Input);
+
+  // Create new register for the input ID builtin variable.
+  Register NewRegister =
+      MIRBuilder.getMRI()->createVirtualRegister(GR.getRegClass(PtrType));
+  MIRBuilder.getMRI()->setType(
+      NewRegister,
+      LLT::pointer(storageClassToAddressSpace(SPIRV::StorageClass::Input),
+                   GR.getPointerSize()));
+  GR.assignSPIRVTypeToVReg(PtrType, NewRegister, MIRBuilder.getMF());
+
+  // Build global variable with the necessary decorations for the input ID
+  // builtin variable.
+  Register Variable = GR.buildGlobalVariable(
+      NewRegister, PtrType, getLinkStringForBuiltIn(BuiltInValue), nullptr,
+      SPIRV::StorageClass::Input, nullptr, true, true,
+      SPIRV::LinkageType::Import, MIRBuilder, false);
----------------
s-perron wrote:

Changing this to false will build a variable without any linkage attribute.

```suggestion
  Register Variable = GR.buildGlobalVariable(
      NewRegister, PtrType, getLinkStringForBuiltIn(BuiltInValue), nullptr,
      SPIRV::StorageClass::Input, nullptr, true, false,
      SPIRV::LinkageType::Import, MIRBuilder, false);
```

https://github.com/llvm/llvm-project/pull/130670