[llvm] [DAG] Handle truncated splat in isBoolConstant (PR #145473)

[Simon Pilgrim via llvm-commits]

================
@@ -4375,6 +4375,8 @@ class LLVM_ABI TargetLowering : public TargetLoweringBase {
            Op.getOpcode() == ISD::SPLAT_VECTOR_PARTS;
   }
 
+  virtual bool isTargetCanonicalSelect(SDNode *N) const { return false; }
----------------
RKSimon wrote:

I have no strong preference tbh and if you want to go with isTargetCanonicalSelect I won't object.

I agree with @arsenm that we add extra TLI hooks too quickly (and seldom get rid of ones that are no longer necessary), but #145724 is not ideal as an alternative.

https://github.com/llvm/llvm-project/pull/145473