[llvm] [LoopUnrollPass] Don't pre-set `UP.Count` before legality checks in `computeUnrollCount()` (PR #185979)

[Jinsong Ji via llvm-commits]

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@@ -1054,9 +1054,8 @@ void llvm::computeUnrollCount(Loop *L, const TargetTransformInfo &TTI,
   // 3rd priority is exact full unrolling.  This will eliminate all copies
   // of some exit test.
   LLVM_DEBUG(dbgs().indent(1) << "Trying full unroll...\n");
-  UP.Count = 0;
+  assert(UP.Count == 0);
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jsji wrote:

This assert is causing issues when we set non-zero UP.Count in getUnrollingPreferences. Can you have a further look? Thanks!

https://github.com/llvm/llvm-project/pull/185979