[llvm] [InstCombine] Optimize powi(X, Y)/ (X * Z) with Ofast (PR #87047)

[Matt Arsenault via llvm-commits]

================
@@ -401,6 +401,18 @@ define double @fdiv_pow_powi_negative_variable(double %x, i32 %y) {
   ret double %div
 }
 
+; powi(X,C1)/ (X * Z) --> powi(X,C1 - 1)/ Z
----------------
arsenm wrote:

The final result doesn't have the divide in the comment? 

https://github.com/llvm/llvm-project/pull/87047