[llvm] [VPlan] Sink vector loop region recipes in licm (PR #172343)

[Mel Chen via llvm-commits]

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@@ -2521,6 +2521,34 @@ static void licm(VPlan &Plan) {
       R.moveBefore(*Preheader, Preheader->end());
     }
   }
+
+  // Sink any recipes which don't have any users in the region to the nearest
+  // common dominator of its users.
+  VPDominatorTree VPDT(Plan);
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_post_order_shallow(LoopRegion->getEntry()))) {
+    for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB))) {
+      if (cannotHoistOrSinkRecipe(R))
+        continue;
+      SmallSetVector<VPBasicBlock *, 4> UserVPBBs;
+      // Check that R doesn't have any users inside a loop region.
+      if (any_of(R.definedValues(), [&UserVPBBs](VPValue *V) {
+            return any_of(V->users(), [&UserVPBBs](VPUser *U) {
+              auto *UR = cast<VPRecipeBase>(U);
+              UserVPBBs.insert(UR->getParent());
+              return UR->getParent()->getEnclosingLoopRegion();
+            });
+          }))
+        continue;
+      if (UserVPBBs.empty())
+        continue;
+      VPBasicBlock *SinkVPBB = UserVPBBs.front();
+      for (auto *UserVPBB : drop_begin(UserVPBBs))
+        SinkVPBB = cast<VPBasicBlock>(
+            VPDT.findNearestCommonDominator(SinkVPBB, UserVPBB));
+      R.moveBefore(*SinkVPBB, SinkVPBB->begin());
----------------
Mel-Chen wrote:

Should not insert to `SinkVPBB->getFirstNonPhi()`? Like: https://github.com/llvm/llvm-project/pull/168031/files#diff-53267225b83e943ceae51c326c9941e323fd7aaf74a08b5e6998d6456f88d1ddR2544

https://github.com/llvm/llvm-project/pull/172343