[llvm] [VPlan] Account for early-exit dispatch blocks when updating LI. (PR #185618)

[Luke Lau via llvm-commits]

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@@ -965,6 +965,32 @@ void VPlan::execute(VPTransformState *State) {
   for (VPBlockBase *Block : RPOT)
     Block->execute(State);
 
+  if (hasEarlyExit()) {
+    // Fix up LoopInfo for extra dispatch blocks when vectorizing loops with
+    // early exits. For dispatch blocks, we need to find the smallest common
+    // loop of all successors. Note: we only need to update loop info for blocks
+    // after the middle block, but there is no easy way to get those at this
+    // point.
+    for (VPBlockBase *VPB : reverse(RPOT)) {
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lukel97 wrote:

I guess we could do a vp_post_order traversal but it's probably best to reuse the existing RPOT instead of recomputing it

https://github.com/llvm/llvm-project/pull/185618