[llvm] [LV] Provide utility routine to find uncounted exit recipes (PR #152530)

[Florian Hahn via llvm-commits]

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@@ -141,3 +141,101 @@ VPBasicBlock *vputils::getFirstLoopHeader(VPlan &Plan, VPDominatorTree &VPDT) {
   });
   return I == DepthFirst.end() ? nullptr : cast<VPBasicBlock>(*I);
 }
+
+std::optional<VPValue *>
+vputils::getRecipesForUncountableExit(VPlan &Plan,
+                                      SmallVectorImpl<VPRecipeBase *> &Recipes,
+                                      SmallVectorImpl<VPRecipeBase *> &GEPs) {
+  using namespace llvm::VPlanPatternMatch;
+  // Given a VPlan like the following (just including the recipes contributing
+  // to loop control exiting here, not the actual work), we're looking to match
+  // the recipes contributing to the uncountable exit condition comparison
+  // (here, vp<%4>) back to either live-ins or the address nodes for the load
+  // used as part of the uncountable exit comparison so that we can copy them
+  // to a preheader and rotate the address in the loop to the next vector
+  // iteration.
+  //
+  // Currently, the address of the load is restricted to a GEP with 2 operands
+  // and a loop invariant base address. This constraint may be relaxed later.
----------------
fhahn wrote:

```suggestion
  // and a live-in base address. This constraint may be relaxed later.
```

https://github.com/llvm/llvm-project/pull/152530