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

[Matt Arsenault via llvm-commits]

================
@@ -124,6 +130,8 @@ void AMDGPUTTIImpl::getUnrollingPreferences(
   // We want to run unroll even for the loops which have been vectorized.
   UP.UnrollVectorizedLoop = true;
 
+  UP.AllowExpensiveTripCount = UnrollRuntimeExpensiveTripCount;
----------------
arsenm wrote:

I assume just setting in gatherUnrollingPreferences will work?

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