[llvm] [VPlan] Preserve IR flags when widening casts (PR #115373)

[Yingwei Zheng via llvm-commits]

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@@ -0,0 +1,78 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes="default<O3>,loop-vectorize" -force-vector-interleave=1 -force-vector-width=4 -S < %s | FileCheck %s
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dtcxzyw wrote:

```suggestion
; RUN: opt -passes=loop-vectorize -force-vector-interleave=1 -force-vector-width=4 -S < %s | FileCheck %s
```


https://github.com/llvm/llvm-project/pull/115373