[llvm] [NFC][SPIRV] Rename `selectSelectDefaultArgs` to `selectExtendBool` (PR #184120)

[Juan Manuel Martinez Caamaño via llvm-commits]

================
@@ -266,8 +266,8 @@ class SPIRVInstructionSelector : public InstructionSelector {
 
   bool selectSelect(Register ResVReg, SPIRVTypeInst ResType,
                     MachineInstr &I) const;
-  bool selectSelectDefaultArgs(Register ResVReg, SPIRVTypeInst ResType,
-                               MachineInstr &I, bool IsSigned) const;
+  bool selectExtendBool(Register ResVReg, SPIRVTypeInst ResType,
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jmmartinez wrote:

I don't agree. This code is not generating code for a generic "int select" pattern.

As far as I understand, this function is used to generate the code that casts a `bool` or `<bool x N>` into a `int/unsigned` or `<int/unsigned x N>`. It is implemented using `OpSelectSISCond/OpSelectVIVCond`, but that is an implementation detail that could change.

What do you think about this name (and adding the boolean register as a parameter):

```cpp
bool generateCastBoolToInt(Register ResVReg, SPIRVTypeInst ResType, bool IsSigned, Register BooleanSrcVReg, MachineInstr &InsertAt) const;
```

https://github.com/llvm/llvm-project/pull/184120