[clang] [compiler-rt] [llvm] [TargetLowering] Set the default `getCmpLibcallReturnType` to word size (PR #192441)

[Alexander Richardson via cfe-commits]

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@@ -993,11 +993,23 @@ class LLVM_ABI TargetLoweringBase {
   virtual EVT getSetCCResultType(const DataLayout &DL, LLVMContext &Context,
                                  EVT VT) const;
 
+  /// Return the "preferred" register width on this target.
+  virtual unsigned getRegisterWidth(const DataLayout &DL) const {
+    // Currently we assume the register width matches the pointer width.
+    // NOTE: This should match Clang's `getRegisterWidth`.
+    return DL.getAddressSizeInBits(0u);
+  }
+
   /// Return the ValueType for comparison libcalls. Comparison libcalls include
   /// floating point comparison calls, and Ordered/Unordered check calls on
   /// floating point numbers.
-  virtual MVT::SimpleValueType getCmpLibcallReturnType() const {
-    return MVT::i32; // return the default value
+  ///
+  /// This should match `CMP_RESULT` in `compiler-rt` and `CMPtype` in
+  /// `libgcc`. The default return is word-sized. Consider overriding on
+  /// targets that have a cheaper comparison at other sizes.
----------------
arichardson wrote:

```suggestion
  /// targets that have a cheaper comparison at other sizes.
  /// This affects the ABI so be sure to coordinate with
  /// other compiler vendors.
```
Might be worth calling out that this needs to be consistent with GCC/other compilers?

https://github.com/llvm/llvm-project/pull/192441