[llvm] [VPlan] Try to hoist Previous (and operands), if sinking fails for FORs. (PR #108945)

[via llvm-commits]

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@@ -771,6 +771,92 @@ sinkRecurrenceUsersAfterPrevious(VPFirstOrderRecurrencePHIRecipe *FOR,
   return true;
 }
 
+/// Try to hoist \p Previous and its operands before all users of \p FOR.
+static bool hoistPreviousBeforeFORUsers(VPFirstOrderRecurrencePHIRecipe *FOR,
+                                        VPRecipeBase *Previous,
+                                        VPDominatorTree &VPDT) {
+  using namespace llvm::VPlanPatternMatch;
+  if (Previous->mayHaveSideEffects() || Previous->mayReadFromMemory())
+    return false;
+
+  // Collect recipes that need hoisting.
+  SmallVector<VPRecipeBase *> WorkList;
----------------
ayalz wrote:

```suggestion
  SmallVector<VPRecipeBase *> HoistCandidates;
```

https://github.com/llvm/llvm-project/pull/108945