[llvm] [SLP]Improved reduction cost/codegen (PR #118293)

[Philip Reames via llvm-commits]

================
@@ -1613,6 +1613,11 @@ class TargetTransformInfo {
   /// split during legalization. Zero is returned when the answer is unknown.
   unsigned getNumberOfParts(Type *Tp) const;
 
+  /// \return true if \p Tp represents a type, fully occupying whole register,
----------------
preames wrote:

Can you clarify that "fully occupied" means "up to known minimum length", not "dynamically at runtime"?  (i.e. w/zvl256b a runtime VLEN=512 case might only occupy half the register.)

https://github.com/llvm/llvm-project/pull/118293