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

[Steven Perron via llvm-commits]

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@@ -4005,6 +4017,38 @@ 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 *U32Type = GR.getOrCreateSPIRVIntegerType(32, MIRBuilder);
+  const SPIRVType *PtrType = GR.getOrCreateSPIRVPointerType(
+      U32Type, MIRBuilder, SPIRV::StorageClass::Input);
+
+  // Create new register for the input ID builtin variable.
+  Register NewRegister =
+      MIRBuilder.getMRI()->createVirtualRegister(&SPIRV::iIDRegClass);
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s-perron wrote:

It might be better to use `GR.getRegClass(PtrType)` than to hardcode the register class.

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