[llvm] [LoopPeel] Implement initial peeling off the last loop iteration. (PR #139551)

[Eli Friedman via llvm-commits]

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@@ -22,10 +22,13 @@ namespace llvm {
 bool canPeel(const Loop *L);
 
 /// VMap is the value-map that maps instructions from the original loop to
-/// instructions in the last peeled-off iteration.
-bool peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI, ScalarEvolution *SE,
-              DominatorTree &DT, AssumptionCache *AC, bool PreserveLCSSA,
-              ValueToValueMapTy &VMap);
+/// instructions in the last peeled-off iteration. If \p PeelLast is true, peel
+/// off the last \p PeelCount iterations from \p L. In that case, the caller has
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efriedma-quic wrote:

Probably should say what happens if PeelLast is false.

Is "at least 2 iterations" still correct if PeelCount isn't 1?

https://github.com/llvm/llvm-project/pull/139551