[llvm] [TTI][RISCV][SLP] Add IdentityConstantValue option to OperandValueKind for use by SLP and RISCV (PR #228630)

[Simon Pilgrim via llvm-commits]

================
@@ -1324,6 +1324,7 @@ class TargetTransformInfo {
     OK_AnyValue,               // Operand can have any value.
     OK_UniformValue,           // Operand is uniform (splat of a value).
     OK_UniformConstantValue,   // Operand is uniform constant.
+    OK_IdentityConstantValue,  // Operand is the identity vector (0, 1, ...)
----------------
RKSimon wrote:

Won't this be Uniform?

https://github.com/llvm/llvm-project/pull/228630