[llvm] [SPIR-V] Allow intrinsics with aggregate return type to reach GlobalISel (PR #108893)

[Steven Perron via llvm-commits]

================
@@ -1101,6 +1127,71 @@ bool SPIRVInstructionSelector::selectFence(MachineInstr &I) const {
       .constrainAllUses(TII, TRI, RBI);
 }
 
+bool SPIRVInstructionSelector::selectOverflowArith(Register ResVReg,
+                                                   const SPIRVType *ResType,
+                                                   MachineInstr &I,
+                                                   unsigned Opcode) const {
+  Type *ResTy = nullptr;
+  StringRef ResName;
+  if (!GR.findValueAttrs(&I, ResTy, ResName))
+    report_fatal_error(
+        "Not enough info to select the arithmetic with overflow instruction");
+  if (!ResTy->isStructTy())
+    report_fatal_error("Expect struct type result for the arithmetic "
+                       "with overflow instruction");
+  // "Result Type must be from OpTypeStruct. The struct must have two members,
+  // and the two members must be the same type."
+  Type *ResElemTy = cast<StructType>(ResTy)->getElementType(0);
+  ResTy = StructType::create(SmallVector<Type *, 2>{ResElemTy, ResElemTy});
+  // Build SPIR-V types and constant(s) if needed.
+  MachineIRBuilder MIRBuilder(I);
+  SPIRVType *StructType = GR.getOrCreateSPIRVType(
+      ResTy, MIRBuilder, SPIRV::AccessQualifier::ReadWrite, false);
+  assert(I.getNumDefs() > 1 && "Not enought operands");
+  SPIRVType *BoolType = GR.getOrCreateSPIRVBoolType(I, TII);
+  unsigned N = GR.getScalarOrVectorComponentCount(ResType);
+  if (N > 1)
+    BoolType = GR.getOrCreateSPIRVVectorType(BoolType, N, I, TII);
+  Register BoolTypeReg = GR.getSPIRVTypeID(BoolType);
+  Register ZeroReg = buildZerosVal(ResType, I);
+  // A new virtual register to store the result struct.
+  Register StructVReg = MRI->createGenericVirtualRegister(LLT::scalar(64));
+  MRI->setRegClass(StructVReg, &SPIRV::IDRegClass);
+  // Build the result name of needed.
----------------
s-perron wrote:

```suggestion
  // Build the result name if needed.
```

https://github.com/llvm/llvm-project/pull/108893