[llvm] Add flag to enable expensive trip counts for runtime unroll. (PR #171735)

[Matt Arsenault via llvm-commits]

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@@ -178,6 +178,11 @@ static cl::opt<unsigned> PragmaUnrollFullMaxIterations(
     "pragma-unroll-full-max-iterations", cl::init(1'000'000), cl::Hidden,
     cl::desc("Maximum allowed iterations to unroll under pragma unroll full."));
 
+static cl::opt<bool> UnrollRuntimeExpensiveTripCount(
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arsenm wrote:

The user facing preference would be an unroll pragma, not a global flag like for the other cases 

https://github.com/llvm/llvm-project/pull/171735