[llvm] Missing opt with ctlz and shifts of power of 2 constants (#41333) (PR #74175)

[Sizov Nikita via llvm-commits]

================
@@ -514,6 +514,8 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
     return IC.replaceInstUsesWith(II, ConstantInt::getNullValue(II.getType()));
   }
 
+  ConstantInt *CInt;
----------------
snikitav wrote:

If change `ConstantInt` to `Constant` not only constant splat vectors may be handled:
```llvm
----------------------------------------
define <2 x i32> @src(<2 x i32> %#0) {
#1:
  %div = lshr <2 x i32> { 8387584, 1234567 }, %#0
  %ctlz = ctlz <2 x i32> %div, 1
  ret <2 x i32> %ctlz
}
=>
define <2 x i32> @tgt(<2 x i32> %#0) {
#1:
  %ctlz = add <2 x i32> %#0, { 9, 11 }
  ret <2 x i32> %ctlz
}
Transformation seems to be correct!
```

https://github.com/llvm/llvm-project/pull/74175