[llvm] [ConstraintElim] Bound non-increasing header IVs by start value. (PR #217921)

[Florian Hahn via llvm-commits]

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@@ -159,3 +161,54 @@ else:
   %res = phi i64 [ %v, %cont ], [ 0, %entry ]
   ret i64 %res
 }
+
+define void @shl_flags(i32 %n) {
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fhahn wrote:

Added a TODO that we should be able preserve `shl nuw`, thanks

https://github.com/llvm/llvm-project/pull/217921