[llvm] [SPIRV] Add a `SPIRVTypeInst` type with some guardrails (PR #179947)

[Juan Manuel Martinez Caamaño via llvm-commits]

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@@ -140,6 +143,9 @@ SPIRVTargetLowering::getRegForInlineAsmConstraint(const TargetRegisterInfo *TRI,
 
 inline Register getTypeReg(MachineRegisterInfo *MRI, Register OpReg) {
   SPIRVType *TypeInst = MRI->getVRegDef(OpReg);
+  assert(!SPIRVTypeInst::definesATypeRegister(TypeInst) &&
+         "The TypeInst is never a type, because this function doesn't make any "
+         "sense");
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jmmartinez wrote:

I agree with you on that. The assert should not make it into trunk. The idea was to highlight the situation that I triggered me to propose this.

> Shouldn't the function be removed instead?

Ideally yes. To verify if we could remove it, I've tried replacing it by:

```cpp
Register getTypeReg(MachineRegisterInfo *MRI, Register OpReg) { return OpReg; }
```

The lit test pass.

https://github.com/llvm/llvm-project/pull/179947