[llvm] [LoopUnroll] Rotate loop before unrolling inside of UnrollRuntimeLoopRemainder (PR #148243)

[via llvm-commits]

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@@ -32,12 +33,14 @@ class TargetTransformInfo;
 /// header. If the loop header's size exceeds the threshold, the loop rotation
 /// will give up. The flag IsUtilMode controls the heuristic used in the
 /// LoopRotation. If it is true, the profitability heuristic will be ignored.
-LLVM_ABI bool LoopRotation(Loop *L, LoopInfo *LI,
-                           const TargetTransformInfo *TTI, AssumptionCache *AC,
-                           DominatorTree *DT, ScalarEvolution *SE,
-                           MemorySSAUpdater *MSSAU, const SimplifyQuery &SQ,
-                           bool RotationOnly, unsigned Threshold,
-                           bool IsUtilMode, bool PrepareForLTO = false);
+/// The ProfitabilityCheck function can override general profitability check.
+LLVM_ABI bool LoopRotation(
+    Loop *L, LoopInfo *LI, const TargetTransformInfo *TTI, AssumptionCache *AC,
+    DominatorTree *DT, ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
+    const SimplifyQuery &SQ, bool RotationOnly, unsigned Threshold,
+    bool IsUtilMode, bool PrepareForLTO = false,
+    function_ref<bool(Loop *, ScalarEvolution *)> ProfitabilityCheck =
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annamthomas wrote:

I think it makes sense as a boolean argument for now. We don't have a strong usecase for a filter function. 
If any refactoring will be done, we can think of how the filter function fits in then.

https://github.com/llvm/llvm-project/pull/148243